Tektronix 2215 Scope repair

[tautech]

What about taking a pic of the PCB and importing it into Paint or a similar basic editor and highlighting the ones you need there ?

WRT the big schematics, use the printer settings to print them on say 4x A4 pages not just 'fit to page' as some printer do. Use Print Preview to see what other available printer settings can offer you. 

[Vince]

What about taking a pic of the PCB and importing it into Paint or a similar basic editor and highlighting the ones you need there ?

Yeah, but the computer is in the living room, and lab/scope is upstairs... so every time I need to take notes, I need to have it in printed/paper form so I can then get upstairs and annotate it. But yes I do use pictures as well, to document the disassembly process, help me when I need to put it back together again. In this case I took that close up shot of the SMPS so I could have an overview of all the caps I was interested in, and remember where were fitted the non-original caps for example.

Printing the picture is not really an option I fancy, because fuil size pics are painfully slow to compute/print, and since my 21 year old HP LaserJet 6P printer is only black and white, pic is grey scale and this gives poor contrast and makes pen writing hard to see no matter what colour I use. A black and white schematic however, is ideal. Excellent contrast, easy on the eye, and can use any pen color I like, they are all easy to see.

I am thinking of upgrading this old B&W laser printer to an A3 colour laser, but good ones still cost a bit of money (by my standards anyway). Plus, I just love this old Laserjet 6P. Cost me a month worth of salary when I bought it new in 1997, but look, 21 years later, still works/prints perfectly, and cost per page is ridiculously low compared to an inkjet printer : the original toner/cartridge lasted 4000 pages.. exactly what its advertised life expectancy was ! Replaced the cartridge 10 years ago... still running !  Just printed the status page to give it a check : counter reports 5121 printed pages, so about 1200 pages using the new/second toner, still 2800 pages to go ! 

I mean... it's worth nothing on the used market, absolutely nothing. So why sell it ? I like it very much, works like it were brand new, cost per page is next to nil... it's the ultimate weapon to print regular A4 pages from manuals and datasheet etc !  .... except it's not the best choice for printing foldouts... or colour pictures, or colour charts, or web pages...

WRT the big schematics, use the printer settings to print them on say 4x A4 pages not just 'fit to page' as some printer do. Use Print Preview to see what other available printer settings can offer you. 

Yeah that would be great ! But historically, printer drivers in Linux, when you are lucky enough to have one available for your printer... well typically they aren't quite as feature-full as their Windows OEM counterpart.   In the case at hand, the driver lets me put several pages on a single sheet of paper, but not spread a single page/foldout onto multiple sheets..  too bad...

Short term I think the best bang for buck would be as I said to get a cheap A3  B&W inkjet printer and try to find a PDF reader that can let you select/print a portion of a page rather than the whole page. That seems like an attainable goal. The small plotter would be in my dreams, but sure would be ideal....

[tautech]

I have a HP 6MP too and it's been a great printer but we also have a 1200dpi color OKI too but we still use them both. With Windows the printer drivers or pdf viewing SW has allowed several printing options that can help get you the types of prints you need.
Yeah I get not having a PC near your bench is a curse and something I quickly dealt to years ago when I did lots of repairs.
A PC close and handy to the bench is just as valuable as your test equipment IMHO.

[wasyoungonce]

If you want schematics printed download them to USB and rake them to your local office print store. 

There are more than a few around us and I live on the edge of civilisation!  large scale sized prints, A2, are really not that expensive.


Sent from my iPhone using Tapatalk

[Vince]

Yeah I get not having a PC near your bench is a curse and something I quickly dealt to years ago when I did lots of repairs.
A PC close and handy to the bench is just as valuable as your test equipment IMHO.

I agree.... it's on the cards ! Problem is that my "vintage" computer (mid '90's IBM "Aptiva") already takes that spot in the lab, with it's bulky tower case and CRT monitor...so no space left for a more modern/useful PC.

But in 6 months or so I will hopefully move into my own house, so will have more space. Will move the old IBM somewhere else, so I can put a more modern machine to serve all the lab duties. Think I will take a flat/ LCD monitor, and very compact computer case in the style of the old "mac mini" (but won't be a Mac), so that it takes as little space as possible. After all I don't need much processing power nor I/Os : a few USB ports, Ethernet for internet, a "true" RS232 port, VGA output and that's about it...

Hopefully I can find such a computer for cheap. I mean my current desktop/main PC is 10 year old (and 3 months...), yet still plenty fast enough for an,ything I have wanted/needed to do with it. A core2 duo 2.66GH, P8GB of RAM. So I would try to find similar specs but in much more compact form factor. Hell, a 20 bucks Raspberry Pi might even be plenty powerful enough ! LOL Don't know, but probably...

[Vince]

If you want schematics printed download them to USB and rake them to your local office print store. 

There are more than a few around us and I live on the edge of civilisation!  large scale sized prints, A2, are really not that expensive.

Hi WasYoungOnce,

I don't have such store in my little 4000 people village (with as many cows, hens, horses, sheeps etc....). I would have to go down town, about 15kms away, 30kms round trip. About 2 liters of fuel, at about 2 US dollars (equivalent of) per liter, 4 bucks + the cost of a parking space, say one buck if I make it quick to the store. so 5 bucks just to get there, not mention the time spent, about an hour and a half total. Plus the fact I could go there only on Saturdays because no time during the week, store would be closed by the time I get there after work.
To make it worth the trip I would have to print the full set of schematics, several times (usually I need more than just one print of a given schematic), which would add up to a sensible amount.... and 90% of that would be wasted because I would obviously not need several prints of each and every page... but of course you only know this once the repair is finished...

So.... it's both highly impractical as well as economically disastrous, from my point of view anyway... YMMV 

My best alternative to date, is to print them at work. Put the manual on a USB stick as you said, and printed at work, on the big A3 "do it all" Xerox copy machine.  Gave it a try today. I printed a selection of schematic sheets, to cover all use cases (exploded view, board layout with component designators, block diagrams, schematics...).  They use Acrobat Reader ' X ' (no idea how old it is.. but copyright states states it's up 2011), and it does have the lovely feature I was dreaming about : you can just select a portion of foldout, and print just that, and make it fit to an A3 page. Most foldouts are 3 page wide, however schematics always use only 2 of the 3 pages, the last one is usually used to show whatever else : a table with component coordinates, waveforms, some text, whatever.
So the schematics are actually A3 sized.... so printed on A3 sheets, they came out just fine.... no need for a plotter in the end, great !
The only 3 page foldout where the "object" actually spans the full width of the foldout, is the block diagram that represents the entire scope. But the requirements for a block diagram, is not as demanding as schematic. (no small prints to read, no need to annotate it all over the shop etc), so when shrunk a little to fit it to A3, it's still perfectly usable, no eye strain.

So looks like this is it then. I need to open the service manual in a Windows virtual machine so I can use Acrobat reader and have this feature that lets me select an arbitrary area of a page, and print it in full res. Then just get a cheap A3 B&W inkjet printer and call it done   Hardest part for me would probably be to get that old parallel port LaserJet to work from VirtualBox.... configuring VM to get direct access to H/W resources is not my strongest point !
But well, it's worth the trouble since It would solve my problem and make me happy !! 
I am sure there is no shortage of people on XYZ forums to help out with configuring the VM...

OK once I have moved into the house late this years : get a new PC for all lab duties, and an A3 printer, and that will breath new life into my "repairing old stuff" activities !

OK so now let's order all those replacement caps... should be able to get them in time to fit them this week-end, hopefully.

[Vince]

Alright... knobs.... 

To sum it up : the knob "situation" on the 22XX scopes is.... appalling. My worst nightmare... it's not even a question of money and economical viability.. it's simply a matter of plain availability !

I need 4 of these little snap-on knobs to fix my 2232. Been a year. Two major sources are "Sphere in america, and "Qservice" in the US but who luckily also have operations in Europe (Greece) which means affordable shipping for me, as well as absence of customs. Still, after a year, neither have these knobs. Sphere has "close enough" models, but not quite what I need, and they cost 15 dollars EACH, and they only have 5 of them. Add shipping and customs, and that's 100 bucks for 4 little knobs that may just as well break like the old ones, when I go to fit them.

As for the sweep knob for the 2215, again none at Qservice (listed but no stock). Sphere has one but 15 bucks... says it comes complete, with the center core (I guess that refers to the little part I broke/need ... but no guarantee ).  Add all the charges and it comes to me.. it will be worth as much as what I paid for the scope itself !

So I am still trying to find a place that would sell/detail this kind of part... but no luck so far.
Spent some time on-line about it... think I know the correct English vocable/terminology now... helps a lot in finding what I need.

The most common knobs with screws on side, are called "set screw" knobs.
The model I need, with a hidden central nut, are called "collet" type knobs. The part I broke is precisely called "collet", which gave its name to this type of knob.
Then there are two types of collets :  ones which are tightened using a screw, and those which use a nut. The latter is obviously the only type which allows a shaft to go through it, so that's what I need. Looks like they are called "through-hole" collets.

So far I have been unable to find a hardware store that would sell individual collets. Everytime I try search for "buy through-hole collet", I am directed to shops that sell tools for metal metal machining : lathe etc ), so not quite what I am after.

My only option I see for now, is to buy a cheap complete collet knob, so I can destroy it and salvage the collet from it..; hoping its collet (dimensions) would fit the Tek sweep knobs (tooks all necessary measurements from it).

But... yeah, again it's not that simple : after a fair bit of searching, it appears that knobs using through-hole collets... are only large knobs for large 1/4" shafts, and the small knobs for 1/8" shaft like the Tek shaft, use screws not nuts, so no use for me.  I understand why this is.. the rationale being that when you stack two knobs, only the biggest knob needs to be through hole, and the small knob doesn't need to be through-hole, because it's two small to stack another knob on top of it anyway. ....... soooo, even buying a new knob is not that easy !  Finding one that is through-hole AND at te same time made for small 1/8" shafts, is a challenge !  After lots of searching, Ebay finally found some for me... the guy sells 3 sizes of theses knobs, so many the collet on one of them can fit the Tek knob, or be made to fit with minor rework. but still... not as cheap an option as I would  like : he only sells them in packs of 2, 4 bucks. Would need to by all 3 models he sells, to get a chance to have one that maybe fits the Tek knob... that's 12 bucks. And the guy is in the US, so again expensive shipping + customs !
And still, no guarantee that one of these knobs would fit !

So... since the complete, proper model knob from Sphere is barely more expensive, at 15 bucks...and would be guaranteed to be the proper model/fit, hence zero risk.... this might still be the "safest" option. So I am thinking of that. Of course I would need to contact Sphere to be 100.00% sure that the knob (unlike what the pics show), DOES come with the collet and nut, as the description suggests.

In the meantime I must still try hard to find a place that might sell/rtail collect, so I could get one locally and dirt cheap. However I getting pessimistic about it : seems to me that no two knobs have similar collets : the shape and dimensions of each and every knobs, calls for customs dimensions, I feel. So I think that knob manufacturers must make (or get made) these collets to their own specifications... 

Still, might post on the forum about this, in case someone knows better and might know where to get this stuff from ! Worth a shot...



CONCLUSION

I think I will have to rethink my "strategy" about these 22XX scopes... this knob problem is a real show stopper. What the point of spending time and money fixing one of these scopes.. if at the end you can't complete the repair because of lack of bloody knobs !    Now I am no purist... fitting a non- Tek part is no trouble to me, as long as it makes sense (like recapping the scope). But as far as knobs go... it's not a matter of being a purist, it's just a matter of aesthetics ! Sorry but there is no way, no way that I can stand the looks of a non original knobs on an instruments, any instrument.. it just ruins the entire "experience", stand out so much, drives me nuts... Some people just don't care, as long as it's functional... I get that. I wish I were like this !  But I am not. Half of the reason I like old gear, is the look and feel of the front panel/user interface. Other half is performance and feature set and engineering quality of course.

So, given that these brittle little knobs are so hard to find, next to impossible, and are so expensive that thety cost as much as the scope... I am now to the point where I think I might have to collect cheap and low end 22XX scopes, ugly, broke,, fallen form the 50th floor, imploded CRT... purely to have spare knobs and switches to help me maintain and fix my main 22XX scope, the ones with good specs and in good nick, which I would actually use.
So I would consider all 22XX scope I can find locally, for say 100 Euros max.

So short term, my revised plan now would be :

- If I fail to find a place that retails collets, then go buy the one from Sphere, once I am sure it does come with the collet.

- Then I could use have a go at troubleshooting this weird dark spot problem trailing behind the intensified portion of the trace.

- Then use the scope as a test best to investigate the SMSP whine issue

... and then store the scope and use it as a donor. I would harvest those snap-on knobs to fix my 2232/main scope. The brand new sweep knobs I might sell to try to recoup some of the cost. I won't sell the scope. It's more useful as a donor for my 2232, and as test bed for the whine issue, and as a sick "patient" to help me learn trouble shooting, improve/build my repair skills. This dark spot issue is really weird. the more weird the issue, the more you have to search for the answer, and the more... you learn. 

So, this little 2215 scope is still very useful in many ways, given the low price I got it for, but yeah, although I will keep it, unless I find cheap push-on knobs, I don't think it will ever complete and used on the bench..

It drives me nuts not be able to use a mint and working scope just because you can't find bloody knobs to complete the front panel, it really drives me mad... but that's what the situation is ! So I must live it and admit that this 2215 scope is more useful and valuable as a parts unit .... 
Working with old gear is sometimes very frustrating indeed... the lack of parts is a pain when it strikes ! 

[Vince]

Grr... I was hoping to get the new caps in time for this week-end, but no luck  !

I ordered from https://www.tme.eu/en/  as often. First class service usually.. but this time some thing is wrong it appears...

- My first order, I canceled at teh last second because I realized I forgot to order one of the caps. So I did NOT enter my credit card number, and I cancelled the process/closed the window and came back to the shopping cart... but somehow they validated this pseudo order, and I received an invoice via e-mail, and the order does show up in my profile/customer space on the web site ?! 

- As soon as I had canceled the first order, I filled my shopping cart all over again, from scratch (it did NOT remember the previous content... crap), then I paid this one normally, and got the invoice in my mail box, as you do. But.... that was 5 days ago, and still no news from them. The order does not appear to be processed at all, they have taken no steps at all... like they are ignoring me ?!  Normally, in 5 days I would already have received my parts ! So something is wrong with them... I sent them an e-mail to inquire about it... hope they will fix the situation promptly.

I want my caps !    That being said... I now realize that I was so focused on ordering the ELECTROLYTIC caps.... that I completely forgot to order the 3 tiny green dipped ceramic caps that go with the PWM chip, oh no !!!!   10 Euros worth of shipping cost to endure again... for 50 cents worth of ceramic caps ?! Tragedy...   

[shakalnokturn]

Should I sell any of these (Tek 2230) before I pack for moving? After that they'll be out of reach for a while...

[Vince]

Hi Paul,

I didn't recall that you had a 2230 !  What happened to it ?!  
You didn't manage to fix it (I can't believe that for a second) and the knobs is all that remains from that scope ? All the rest is gone ? 

Well, that's quite a lot money laid on your bench here ! Wish I had enough money to pay for that... but please don't throw them away... I do intend to hang onto my 2232 as my main scope, for a while, so I would probably buy you the lot in a few months, depending on price...

However unless I am blind (picture is not very high-res), it looks like you did not manage to salvage any of the so precious and rare, britle snap-on knobs, the 4 used for the position controls, the 4 that I broke on my scope.... 

Still, would be nice to have the rest of the knobs, for sure... can't hurt.

I think I will buy another 2232 or tow, in the future, if I can find some moderately priced... yeah not an easy task in our neck of the woods I admit ! 

So your wooden house is finished at last... when do you plan on moving exactly ?? My house is on the way too... hoping to move by the end of the year. Late October with some luck...

[shakalnokturn]

Hello Vincent,

I picked that 2230 up from industrial scrap back in the time I didn't have "that many scopes", I did think of trying to fix it but it was missing the cover and the remains had been crushed a little by a fork-lift, so I actually gave the idea up pretty fast and kept the parts.
I seem to have 5 snap-on knob caps, 2 of which have partially lost the "snap".

The house isn't finished, that's why all this electronics junk will by out of reach for some time, I'm moving in august, into an incomplete place and will have to store the treasure in the meantime.

[Vince]

Hi Paul,

I picked that 2230 up from industrial scrap back in the time I didn't have "that many scopes", I did think of trying to fix it but it was missing the cover and the remains had been crushed a little by a fork-lift, so I actually gave the idea up pretty fast and kept the parts.

Okaaaaay... that poor scope never even stood a chance then... crap 

I seem to have 5 snap-on knob caps, 2 of which have partially lost the "snap".

Ah, some broke. I feel less stupid for breaking mine then...
I am so desperate that I think I might contemplate trying to glue the broken bits inside the knobs.... nothing to lose.
I am glad I have these 2215 as a donor for my 2232. If just for that, it was worth buying it.

Of course we could 3D print these... but the feel, surface finish and colour would never be a good enough match... even if subcontracting the job to a specialized company that use million dollars high-tech printers.  Maybe one day... maybe in 100 years.... until then, harvesting knobs from a donor scope is about the only solution.

The house isn't finished, that's why all this electronics junk will by out of reach for some time, I'm moving in august, into an incomplete place and will have to store the treasure in the meantime.

OK get it.... sorry about the situation. I hope it won't be 2 years before you can bring all your stuff back into the house !
Well come to think of it.. I am pretty much in the same situation ! The lab is supposed to go upstairs, as I don't have a spare room on the ground floor. Only problem is that there won't be an "upstairs" to talk about, until I have turned the attic into a place compatible with the presence of human beings... and this is expected to take 2 or 3 years.  Until then... the lab will actually occupy 60% of the living room... back to the old days then, when I was living in small appartments...

[Vince]

Alllllll - riiiiiiight..... worked a bit on the thing last night...


Recapping

I received a bunch of caps from TME. They have really a great choice of electrolytic caps. Even when narrowing down the search to only Nichicon and 105°C rated caps, I still had the choice between several series of caps ! So what to choose ?! A normal person would just pick the cheapest, or roll a dice.. but of course an electronic guy has to make rational/informed decisions, so I had no choice but to download the data sheet for all these series I was offered.  Mostly VX, VY, PM and PW series, then compare them and try to figure out what would be best.

I am hardly an expert so was not straightforward... but in the end I decided to go for the PW series where possible, else pick PM, but leave the VX and VY alone.  VX and VY look like your cheap and short life high losses filter caps for linear supplies. The 'P' "series of series" so to speak, looks more like it's designed as low ESR for SMPS use, and longer life/endurance. If anything, PM/PW data sheets give you the actual ESR, down to the milli-ohm, for each and every voltage/capacitance combination possible... whereas the VX/VY series don't. They just give you a rough "losses" factor for the entire range of caps, no detail.
Then, when you open a datasheet (all 4 attached below) , they show you a little diagram that links the series to other series... so there you learn about even more series that you didn't even know existed ! More confusion ! Who knew there could be so many different models/types of electrolytic caps ?! 

So to decide between PM or PW, the impression I got was that PW was the slightly improved version of PM, about to supersede it. Slightly lower ESR, longer life, smaller case... though if you look at the tables/hard facts, at least for the caps I was concerned with, the PW was exactly the same package/dimension, not smaller, and the ESR was so marginally smaller that it was not a decisive factor. Like 29mohms vs 30, IIRC.
Still, it was a bit better and meant to replace PM short term. Also, the PW was often much cheaper than the "old" PM.
Then for some of the caps, I swa a 'PS' series, which cost 10 times more than the PW...  IIRC the PS is so outrageously expensive mostly because of its astonishingly high life expectancy, from memory, something like 20,000 hours when the PS and PW are in the 5000/8000 range, and the VX/VY series in the 1,000 range...
So, basically, not all electrolytic caps are the same...you get what you pay for and make an informed decision.


So , I ordered mostly PW, and PM only when the PW was either not available, or its minimum order quantity was like 100 or 500...

Sorry for the long paragraph but well... that's actually what one has to go through when ordering something as simple as caps... nothing is really simple, the more choice you are faced with, the more time you end up spending figuring things out...
Reading the manufacturer datasheets closely is a good way to learn about the subject, when like me you don't know all that much !
I would be interested to see a technical paper from Nichicon or other good brands, that explains the gory details of just what's involved in making a cap last longer than another, and what's involved in achieving a 105 or even 125°C rated cap, compared to a common 85°C cap.

Some caps I ordered 20 of them because they were so small, literally 5 cents a piece, so 20 was the minimum order quantity. Well, I have dozens of caps in my drawers now, can't hurt.

So I replaced all those caps. Went pretty smoothly. Some were a bit of a gamble because the track was on the component side, so you have no way to be sure that the solder flowed through the hole to reach the underside of the cap... all you can do is heat the lead/pad for a decent amount of time to make sure it's well heated, so the solder can flow well and hopefully get to the other side of the PCB.. and add more solder than usual, to make it fill the hole and have some left to make the hidden joint.

I also replaced the 2 caps on the pre-reg board, the ones I had already replaced the other day for test purposes, with crappy caps from my local electronic shop.

Only cap I did not replace, as discussed earlier, is the big 450V mains filter cap. However I did order a couple anyway... just in case I somehow decide to replace it. This I will have them handy. These aren't cheap t 5 Euros a pop, but... even I don't use them on this scope, I could still reuse them later on no problem, since pretty much all SMPS supplies have a 450V electrolytic cap to filter the mains... so these caps aren't wasted, no worries.

That's for electrolytic caps. Sadly TME has an extremely limited selection of dipped ceramic caps, either that or I am blind and did not find them. So I have not yet replaced the 3 little axial green ceramic caps that  revolve around the PWM chip. Will have to order these from some other place, yet to be determined...
Anyway, it didn't bother me too much because the scope was working just fine even with one of these caps missing, and a doubt on the health on the other two. Plus, the pre-reg board is easy to access later anyway, not much involved, so the caps can be replaced any time.




MOSFET

Seeing as the SMPS (main board I mean) was fully recapped, I wanted to put all the shield and pre-reg board in place, so as to have it in it's nominal configuration before testing the supply rails. This meant I had to remember... how to put the FET assembly back together again ! Tried to improvise, no good. Luckily I had a coupe pictures taken during disassembly, that clearly showed how it's put together, phew. Never be afraid of taking loads of pics when you take stuff apart... it will be your savior 6 months later when comes time to put it all back together !  You can never have too much pics... you can never know what picture will be the one that might save your bacon later down the line !

So one thing leading to another.. the legs of the old FET, broke as I had to bend them to put the FET back into its plastic holder/box. Didn't think that soldering the pins would be very elegant nor anything to be proud of, so I took that opportunity to replace the FET with the modern replacement I had bought. I didn't find the usual IRF something model, so had to improvise and just use a parametric search and pick what might be suitable... I stumbled on some weirdly named part I had never heard about, it's a IPP60R280P7  made by Infineon... I thought these guys only made memory chips ?! Apparently not... you live and learn.

PDF (too large to be attached) : 

 https://www.infineon.com/dgdl/Infineon-IPP60R280P7-DS-v02_00-EN.pdf?fileId=5546d4625b10283a015b1f973023047b


This part as one would guess, is at least no paper much better than the old IRF820, which was 2.5Amps and 3.0 ohms RDSon. The Infineon part can sustain at least 8 amps, and RDSon is literally an order of magnitude lower, at 0.28ohm. Sounds almost too good to be true, but well, they had the guts to put that in their datasheet so I guess there must at least some truth to it ! Hell, even if it's only half as good as they say, it would still be much better than the old IRF820 !

Later I realized one pesky detail, ahem... there is one little "detail" that the old IRF820 DOES feature, that I didn't think of taking into account when I search for a replacement : the IRF has an INSULATED tab ! It's not connected to the drain. Oh noooo... need to search for another replacement then... and spend hours pulling datasheets, because the parametric search engine does not offer to search for tab insulation, bummer... would have been too easy eh ?! 

so, I evaluated the risk I was taking by using that my non-insulated replacement...
For one, the FET is not fastened to a heat sink ! Far from that : it's covered by a pretty thick (1mm or so) ceramic "pad", itself covered by what must be (?) some kind of EMI shield, which takes the form of a piece of FR4/fiber glass... that's yet another layer of insulation. So at least it looked like the tab would not make the chassis live and kill me, a good start. Then I looked at the possibility of the tab coming accidentally in contact with whatever in the scope, a lose wire, anything...
but everything in the area is tightly held, and also the FET is not out in the wild far from that : it's completely isolated in its little brown plastic holder/prison... it's covered all around, no way a lose wire, or even a lose screw, could get inside the holder and come to contact the live tab... ).
So, I decided I would solder my replacement FET in place, and put the SMPS all back together again, all the shield and mounting hardware, all in back in one piece again.

Honestly I don't understand how Tek though it was OK to leave the FET swithching the juice all day long, with no heatsink and zero airflow, not even still air.. literally sealed in this plastic holder ?!     More incredible is that despite this, and the high RDSon of 3ohm, hence lots of losses/heat... this FET did not melt !
Or maybe it did and was already replaced once... or twice, or thrice... or frice... LOL ! what should we say after thrice...

Anyway, at leas the modern replacement with it's 10 times lower RDSon, can only help ! Maybe this one won't fry... we shall see.

Testing

Finally, the moment of truth : will it work, will it blow, will I get electrocuted, or or or or.... ?!

Luckily none of the above, I am glad to report ! 

Scope still alive. I checked all the rails one by one. First the reference rail, -8.6V, because all the other rails are tied to this one. It was well within spec so I did not even consider touching the trimmer to try to make it better.  That rail has a very tight tolerance +/-  40mV, and I was down by 15mV. So I left it at that.
All the other rails measure well within spec as well, as could be expected. As for ripple, it was getting late last night, so didn't feel like firing a scope to get the real picture, so instead, I went the cheap route : just checked with a DMM in VAC mode, to get a taste for it.  It's got a very decent RMS bandwidth of 100kHz, and the SMPS switches well below that, at 40kHz for the pre-reg, and only 20kHz for the inverter. So the DMM would get a fair share of the spectrum, the reading would hold water, I thought.  Obviously the manual states Peak to Peak values, not RMS, but well as a rough approximation, I thought well, let's say the RMS shall not be more than half the P-P value, say. Hardly scientific, but well, you get the idea.
So did that... and the DMM showed.... ZERO millitvolt ! Not one. A rock solid, steady zero mV ?! Too good to be true. Couldn't possibly trust that, could I... so I tried another DMM (same specs), and it agreed ! Eh ?! Hmmmm....
So in the end I did eventually fire up a scope, my 2232 as usual, to get a taste of what was really going on.

I was not disappointed, my DMM did not lie to me ! Scope has much higher BW of course, so I do get some ripple, but so tiny ! Max sensitivity of the vertical amplifier is 2mV pr division, and well, I get about one division P-P !  2mV P-P ! Geez !   The manual requires less than 10mV P-P on all the low voltage supplies (5V and symmetrical 8.6V), and I get 2mV only !
30V rail allows for a bit more ripple of course, up to 50mV, and I measure a grand maximum of 25mV worse case, only 15mV when averaging the waveform to get rid of the random crap and get a more stable waveform.  The 100V supply can do with up to 200mV ripple, and I measured a bit less than 100mV. So again well within spec !



Rail     Tolerance   Measured  P-P ripple   Measured
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-8.6V   +/- 40mV    -8,585V   < 10mV      2mV
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+5V     +/- 0.25V    5.03V    < 10mV      2mV
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+8.6V   +/- 260mV    8.54V    < 10mV      2mV
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+30V    +/- 1.5V     30.2V    < 50mV      15 to 25mV
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+100V   +/- 5V       100.3V   < 200mV     < 100mV
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -



Every body likes to see waveforms right, so here they are.


Now I left the best bit for dessert, as you do !

The SMPS is now.... completely.... SILENT ! I don't mean to say "more quiet", or " a lot more quiet", or "whisper quiet"... no, it is become absolutely silent, nothing to be heard what so ever !  I didn't quit expect that ! Was as shocked as I was surprised and pleased ! 

I left it running for a fair bit of time, as I was taking measurements with the DMM and scope on all the rails... but it remained quiet. Powered it off after I had finished testing all the rails. Some time later I powered it back up again, thinking I might have just gotten lucky the first time, and that the noise would reappear.. but it did not ! 

So.... my main project with this scope was to precisely use it as a test bed to investigate the SMPS whine, but now that said whine has suddenly vanished... well !!!  I think I might keep it anyway, for the time being at least, to get some repair experience. So I still intend on giving a shot at fixing the remaining issues with this scope.

So... was it the FET or the new caps that cured the whine ? No idea !  But it sure motivates me to do the long overdue recap on the SMPS of my 2232 ! When I fixed its SMPS last summer, after it blew, I was happy enough that I managed to get it back up and running (was overwhelmed and clueless, so thanks to the guys who helped me back then !), so I didn't feel like messing any more with it... I needed a rest ! LOL
I think now is a good time to recap it :-)

Also, worth noting : I noticed that the 2232 SMPS was unusually quiet and much quicker to go to near silence, than it used to be. Took it say 2 minutes to quiet down, versus maybe 15 or 20 minutes usually !  Only thing I can think of, is that last night when I used it, it was really, really very hot here !
So this is consistent with Tautech's supposition that the whine might be related to a warm up/temperature phenomenon. Based on what happened with the 2215, I guess it's fair to say that it's either the caps and/or the FET that are involved. Given that I had already replaced the FET in the 2232, looks like the caps might be the culprit then !  Could still be the FET I guess, but I have ordered two of them. So if recapping the 2232 doesn't make it quiet, I might try replacing the (new but different model) FET, with the same I used in the 2215. So some more experiments to come ! 

Some pics and straight to bed 

[tautech]

Great outcome Vince, congrats. 

Of course it makes perfect sense to replace that MOSFET with a modern equivalent especially to get lower Rds ON and subsequently much lower losses and heat byproduct.


The only thing else I would do is to bring that -8V rail exactly to spec as it was most likely when new.
So much in a CRO is related to the voltage rails and such a little  should have it behaving just like new. 

Look out 2232..........you're next ! !

[Pete F]

Thanks Vince, I got directed to your thread and it's very timely. I have the same unit to repair, in my case it's blowing fuses. I can hear the high voltage starting but then the fuse blows. Unfortunately I don't have another oscilloscope to capture the start up. I don't want to waste too much time on it, but will try taking out the mosfet to isolate the output and enable the pwm area to be checked.

Did yours have that small PCB shield on the mosfet? I thought the whole method of mounting, with the thermal washer in between was an especially crap design!

[Pete F]

Ok, the mosfet Q933 is blown, any idea what it is? IRF820? Just checking to see if that's the only issue or whether something else took it out.

[Vince]

The only thing else I would do is to bring that -8V rail exactly to spec as it was most likely when new.
So much in a CRO is related to the voltage rails and such a little  should have it behaving just like new. 

OK... I just adjusted it, see picture, not lying ! 

My original measurements I did with my MX 54C, which is 0.05% +2D, not my best meter.  To adjust it spot on well... I would need a fancy super accurate bench voltmeter... one day, but sadly no just yet. So instead I did the best I could, and grabbed my best DMM, a MX 56C, 0.025% +2, twice as good as the MX 54C.
Still, with the "+ 2D" bit, right there we now that even if I adjust it spot on, it might possibly be still be 2mV off !  But well what can you do !

Anyway, before adjusting anything, the MX 56C disagreed with the 54C : the former was more optimistic than the latter, deciding on 8,594 rather than 8.585. So only 6mV down, rather than 15.  So I tweaked the trimmer... as I feared, it was very touchy and at first it made things way worse !    That trimmer gives only coarse adjustment sadly. I eventually managed to get a 8,600V reading, but it's so touchy that I guess that just the act of handling the scope would make it deviate...  let's be honest... 
But well, at least for the picture, it was for a brief moment spot on ! 

I plan on getting on those popular and affordable Voltage reference from these people :

http://www.voltagestandard.com/

It would be a good start and allow me to check all my DMMs (I have over a dozen of them... I think I grew a fetish for these little things, just like I did for CRO's !  ) , until I can afford a precision bench meter.

[Vince]

Thanks Vince, I got directed to your thread and it's very timely. I have the same unit to repair, in my case it's blowing fuses. I can hear the high voltage starting but then the fuse blows. Unfortunately I don't have another oscilloscope to capture the start up. I don't want to waste too much time on it, but will try taking out the mosfet to isolate the output and enable the pwm area to be checked.

Did yours have that small PCB shield on the mosfet? I thought the whole method of mounting, with the thermal washer in between was an especially crap design!

Ok, the mosfet Q933 is blown, any idea what it is? IRF820? Just checking to see if that's the only issue or whether something else took it out.

Hi Pete,

Did you open a thread somewhere to discuss your repair, so I can post there ? Link  please ! 

But to get you started I will answer your first questions here.

First, I encourage you to read the present topic, only two pages. It will answer most of your questions.

- No other scope : do'nt worry, you probably don't need it to get your scope back up and running. I used mine because well, I like to see what's going on and learn from my repairs, but it was not strictly necessary. You just need a decent DMM and a lab power supply.

- as you I describe in the present topic, the very first thing you need to do is to unplug the regulator board, and power the scope/inverter directly from your lab power supply. You will need to set it at 43V and limit the current to something like 750mA, that will do. The scope never draws more than this. This way you will see if the scope is working and the problems limlited to the regulator board. From experience and that of others... most likely the scope survived and only the regulator board needs fixing, but of course YMMV so don't assume anything, just diagnose methodically. The reason for the scope surviving is that the reg board has en efficient crow bar... saves your bacon.

- As a start, let's assume the scope is good and only the regulator board is affected. You can now reconnect the reg board, but of course only the mains terminal, and leave the DC output unconnected. This way the scope is not powered, only the reg board is, and you can now troubleshoot said board, again, methodically...

- Before you plug the reg board, of course do all static checks first ! Look for any signs of damage do the FET blowing (or else...) : burnt components etc.
When my 2232 blew/shorted its FET, half the regulator circuitry blew with it ! .. because basically it dumped the mains into the low voltage PWM circuitry, via the gate of the FET. So had to replace quite a lot of components.  So spend a lot of time checking everything visually, then all passive and active components with your DMM, lifting legs where necessary so as to get a reliable measurement.

- FET type : you say you can't identify the FET on your board ?! Boy it must have suffered really bad then ! 
The FET type is not critical. On my 2215 scope it happens to be an IRF820, but the performance (RDSon/losses) is extremely poor compared to newer parts. So don't try to buy a new IRF820 (assuming they are still available, don't know), just get a better part from whatever supplier you use. As for me, as I explained a short while ago, I picked one at random using a parametric search, and works just fine. So at least you know this one will do the job, but many more will work just as well...

- PCB shield on the FET : yeah as I mentionned, mine has this little thingie as well, see picture below.


So to sum it up the very first thing to do is unplug/pull out the regulator board and power the scope/inverter directly from a lab power supply. Then report ... but on your own thread (will meet you there) not here please, I have enough on my plate with my own very sick 2215 ! 

[Vince]

Recapping : oops, forgot to talk about the B Sweep board recap ! 

There is one single electrolytic cap on that board, buried at the very bottom of it, not very accessible, not with my big fingers any way... was a pain in the butt to replace.

At first I got suspicious/worried because up close, that cap looked like a bodge mod ?! I mean, it has super long leads and is soldered on existing pads, doesn't have pads of its own. So I was suspicious ! Turns out it's indeed a bodge but.. a genuine Tek one ! 

On the schematic, one can see this cap ( C659) is there, it does exist... however when you look at the board view... they clearly forgot to route it !!!   
You can clearly see that they modified the board view by hand to add that cap ! LOL
The real thing on the PCB matches exactly what's on the board view, so I feel relieved... it's an intended mod, not some random hack from some previous owner.  This only goes to illustrate Floobydust comments, when he said that this scope was rushed to market/immature...

Another example : again on this alternate sweep board. The solder joints on the COMPONENT side of pretty much any IC, look horrible at best ! I managed a decent close up picture of one of these IC, as an example. Look for yourself ! Terrible eh ? Most pins have barely any solder at all on them.. and many of them are NOT connected to anything on the track/under side of the PCB, so no savior to be expected there ! One of the pins even looks corroded to me ?! The last one on the far right.  I don't know where that corrosion might have come though ! There is only that one lonely cap on the board, and it's at the very bottom, I don't see how it could have spread/vented its electrolyte this far up the board ?!

So I think this really motivates me to desolder that board (27 pins in one row, double sided... yike, will be "fun"    ) so I can have good access to it and redo all the joint on all these ICs.   I already have some connectors to solder to the board, ordered them along with the caps. Might solve my "dark spot" problem when delayed sweep is enabled. However... after fiddling with the scope some more... I think I have bigger problems to worry about that this dark spot !  The MAIN time base is playing up ! Well, I do'nt think the TB itself is at fault, but on many sweep speed settings, the trace just disappears ! Sometimes fiddling with the brightness control brings them back , somehow ! Trouble is that it all seem random, inconsistent... trace would fail to display at a given sweep speed...once, but 2 minutes later it might work just fine on the same setting ! So it's hard to trouble shoot random problems !  I have already cleaned and exercised the sweep switch(es) thoroughly. It switches very cleanly, I don't think there is anything wrong with it. But well, hardly an expert.. first time I have to work in this area of an analog  scope.

Anyway, must gut feeling is that it's this dreaded brightness auto-control feature that's playing up !

I have to try and play some more with the scope until I can hopefully try to find a case/scenario where I can have a reliable/repeatable fault, so I have actually something tangible to chase/trouble-shoot ! Then hopefully once this is fixed, it will fix all the other seemingly random faults.... hopefully !

At least now I know that what ever is wrong, it's not due to crappy power rails ! All new caps, DC levels are spot on and ripple is waaay within spec.
So now I know I have a "real" problem to investigate.

To be honest this auto-brightness feature looks such a pain to understand, I am not sure I will have the courage to dig into the subject far and long enough to get to the bottom of it...  I will try, so as to learn a little something about it, but I am not so sure I will be able to fix it....   

For now, bed time... 

[Pete F]

Thanks Vince, I got directed to your thread and it's very timely. I have the same unit to repair, in my case it's blowing fuses. I can hear the high voltage starting but then the fuse blows. Unfortunately I don't have another oscilloscope to capture the start up. I don't want to waste too much time on it, but will try taking out the mosfet to isolate the output and enable the pwm area to be checked.

Did yours have that small PCB shield on the mosfet? I thought the whole method of mounting, with the thermal washer in between was an especially crap design!

Ok, the mosfet Q933 is blown, any idea what it is? IRF820? Just checking to see if that's the only issue or whether something else took it out.

Hi Pete,

Did you open a thread somewhere to discuss your repair, so I can post there ? Link  please ! 

But to get you started I will answer your first questions here.

First, I encourage you to read the present topic, only two pages. It will answer most of your questions.

- No other scope : do'nt worry, you probably don't need it to get your scope back up and running. I used mine because well, I like to see what's going on and learn from my repairs, but it was not strictly necessary. You just need a decent DMM and a lab power supply.

- as you I describe in the present topic, the very first thing you need to do is to unplug the regulator board, and power the scope/inverter directly from your lab power supply. You will need to set it at 43V and limit the current to something like 750mA, that will do. The scope never draws more than this. This way you will see if the scope is working and the problems limlited to the regulator board. From experience and that of others... most likely the scope survived and only the regulator board needs fixing, but of course YMMV so don't assume anything, just diagnose methodically. The reason for the scope surviving is that the reg board has en efficient crow bar... saves your bacon.

- As a start, let's assume the scope is good and only the regulator board is affected. You can now reconnect the reg board, but of course only the mains terminal, and leave the DC output unconnected. This way the scope is not powered, only the reg board is, and you can now troubleshoot said board, again, methodically...

- Before you plug the reg board, of course do all static checks first ! Look for any signs of damage do the FET blowing (or else...) : burnt components etc.
When my 2232 blew/shorted its FET, half the regulator circuitry blew with it ! .. because basically it dumped the mains into the low voltage PWM circuitry, via the gate of the FET. So had to replace quite a lot of components.  So spend a lot of time checking everything visually, then all passive and active components with your DMM, lifting legs where necessary so as to get a reliable measurement.

- FET type : you say you can't identify the FET on your board ?! Boy it must have suffered really bad then ! 
The FET type is not critical. On my 2215 scope it happens to be an IRF820, but the performance (RDSon/losses) is extremely poor compared to newer parts. So don't try to buy a new IRF820 (assuming they are still available, don't know), just get a better part from whatever supplier you use. As for me, as I explained a short while ago, I picked one at random using a parametric search, and works just fine. So at least you know this one will do the job, but many more will work just as well...

- PCB shield on the FET : yeah as I mentionned, mine has this little thingie as well, see picture below.


So to sum it up the very first thing to do is unplug/pull out the regulator board and power the scope/inverter directly from a lab power supply. Then report ... but on your own thread (will meet you there) not here please, I have enough on my plate with my own very sick 2215 ! 

I didn't start a thread on my repair, I didn't see the point. If somebody is searching for this information in future they can find it all here.

Did you in fact read what I posted here? Shortly after the first question I posted the answer. The fault is a blown mosfet Q933. I believe it is an IRF820, so some more have been ordered (they are cheap so ordered some spares in case there's still an issue that caused it to fail). I have checked through the board as best I can and can't see any other obvious failures at this stage. The arrangement for mounting the mosfet is without doubt the most terrible design for that that I have ever seen. Looking at the evidence I suspect what may have happened is some condensation or other contamination has caused a short between that stupid little shielding PCB and the mosfet itself. When it failed there was smoke, crackling noise etc, yet no obvious signs on the components. Most strange. However the copper on the PCB seems to be eroded, so I believe it's tracked to there, eroded the copper and eventually caused an outright failure of the mosfet, as 'lectricity was going places it was never supposed to go! The proof will however be once the replacement was installed. When I was doing this type of work for my occupation I'd always like to satisfy myself as to WHY a component failed and not just WHAT component failed. It may have taken a bit longer but I very rarely got any jobs returning

[Vince]

Did you in fact read what I posted here? Shortly after the first question I posted the answer. The fault is a blown mosfet Q933.

Yep I read that !    But all you said was that you found that the FET was blown. You didn't say that you actually had found the root cause of the problem, nor what other components may have been damaged.  So it was not clear whether you wanted any more help to take it further 'till the scope is actually fixed and running, or if you were happy to just stop there.

Now I know ! 

[Pete F]

Yes I was happy that the mosfet was the only issue. The graphics on it had faded so it was difficult to read, in the end I just ordered a new IRF820, and it seems to be running ok. I replaced the 2 main electrolytics on that board too, simply because the original ones were old. I'll leave it running on soak for a while to make sure it doesn't poop itself again.

It still has a switch that is dirty for the 1/1+2/2 channels. I'd tried cleaning it with spray but it look like I will need to get more serious with it. I may as well go through the functions and fix little annoying things like that to repair them while it's open.

I was ready to literally throw this in the bin, but it was dark and raining at the time, so it sat inside. Luckily the next day I decided to give it another chance and have a look if a repair was reasonably possible and practical. The total cost was A$1.50 but I decided to buy some extras so let's call it $5 for the parts and fuses. Not too bad to get it running again

[Pete F]

Ok that channel switch finished up cleaning up ok. I have one faulty probe, so I'll need to get another one tomorrow, but other than that it all now seems to be working correctly.

Good luck with yours.

[Vince]

Yes I was happy that the mosfet was the only issue. The graphics on it had faded so it was difficult to read,

OK OK... I understand better now. At first you said it was "blown", then " I can't read the part number on it"... so I assumed the FET really blew or overheated badly, and its case either cracked or popped, or the ink melted...  which is why I thought that the rgulator board suffered a catastrophic failure and that therefore, like happened in my 2232, half of the board need to be replaced ! But your latest comments look like the FET failed OPEN, not shorted, so yeah that'(s good luck as the FET didn't bring anything down with it... 

I was ready to literally throw this in the bin, but it was dark and raining at the time, so it sat inside. Luckily the next day I decided to give it another chance and have a look if a repair was reasonably possible and practical. The total cost was A$1.50 but I decided to buy some extras so let's call it $5 for the parts and fuses. Not too bad to get it running again

Yeah, always worth a shot, you never know your luck    Mine didn't even power up, and it was all due to a tiny 10 cents Zener diode on that regulator board ! 10 cents and it was back to life !    Well of course I still have other issues t fix now, but the show-stopper one has been fixed quickly and very cheaply.

[Pete F]

To be good in repair never assume anything, always keep an open mind, even if you my think something is obvious

The MOSFET failed short circuit, hence why it was blowing fuses. Had it failed open circuit the circuit wouldn't have power up. It's why I pulled that out to isolate it, then tested it to find it was a short and I didn't need to look for the fault, it was in my hand. Then just test the (now isolated circuit) to see if everything else seemed to look ok.