Tektronix 465 w/ DM44 subject to whims.

[Malefoda]

Hello,
I'm new to this board and have been advised to come here by the DIYAudio fellows about my Tek scope. I'm also happy to watch these videos of Dave
I'm no engineer but can learn , years ago I had no idea what a resistors was and here I am making simple circuits and using a scope and signal generator =)

The 465 has been given free to me with the "stopped working" note. First I've put the main selector to 230V, then powered on. All lights on but no trace at all.
Tried it some more times and one day, all of a sudden, it worked!
I've used it a couple of days, even powered it just to let it warm sometimes. Once power off made a bright flash on screen, almost painfull to see and also like a static discharge noise on startup. But tonight here it goes again, no trace at all. Seems the fan is on a very slow speed also.

Several threads, the service manual but it looks too big for me... What about a first control by sight with case removed  , maybe pictures? Or some of you with already some ideas?
And I wonder why I don't have the lovely knob on the delay pot...

Thanks!
Matthieu

[tautech]

Welcome to the forum.

Link the SM so we can all be on the same page as you are.
Grab this Tek doc too, it gives good basic guidance:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

Study the SM, really study it....pull the case off and get to the point where you know where things that are mentioned in the SM actually physically are. Take your time and become familiar with it's guts and mark test points if they aren't identified.
Common failure points for CRO's are the EHT circuitry for the CRT, the LV supplies and occasionally the PDA.
Start with checking the basics, the low voltage PSU rails. They must be to spec as outlined in the SM.

Others that are more familiar with the 465 will likely chime in with good advice too.
Good luck with your 465.

[tggzzz]

Measure the voltage and ripple on all the PSU rails, compare with the values in the service manual.

Expect to find electrolytic capacitors which have "dried out" and need replacing. Typical symptom: too much ripple.
Expect to find tantalum capacitors which have gone short-circuit and need replacing.
Expect to find oxide on pots/switches which needs removing by repeated operation and/or fluff removal and/or IPA/Caig Deoxcit. Typical symptom: noisy operation and/or only some ranges work.

Beware of the high voltages and find where they are; some are dangerous.

There are many threads on this forum about those topics.

[barry14]

I can't help with your problem but I can answer your question about the delay knob.  It is not a calibrated 10 turn knob because the delay time is read out on the digital display of the DM44.  You should consult the manual for details.

[Lorenzo_1]

If you look through 1861-1A to 1861-5 of the Tek465 service manual on Electrotanya, there's a very thorough troubleshooting procedure for this sort of display problem. Like you, I'm far from expert on this stuff. But I have fixed my Tek485 power supply and HV circuit a few times with help from forum members.  I had to do a lot of research and reading before I was game to probe into the HV end of the power supply - there's dangerous voltages in there, as others have noted.   If you follow the manual, you'll quickly encounter a step requiring testing of the -2450V supply.  I'd try to exhaust all other possibilities on the low voltage side before even thinking about probing the HV side, which carries considerably higher risks. 

As suggested by tautech, you will need to spend quite some time working out where your low and high voltages are so you know what you're probing at and also studying the schematics and theory of operation in the service manual.  I have found it useful to read and re-read them repeatedly as my understanding improves. There's also much useful reading here and elsewhere about good and bad practice when working in and around power supplies - they're worth investing time in as well. Good bedtime reading...

[Malefoda]

Thanks all ,
ok will do my homework and have in mind that kid must be away as there is potential danger and the fact I'll do it in the kitchen. And need to borrow a second scope when it's ripple time.
Will use the Tek465 service manual on Electrotanya https://elektrotanya.com/tektronix_465_oscilloscope_full_sm.pdf/download.html , thanks Lorenzo_1, (I have no B on my serial, is that ok?...and can't even figure out what is the 1861-1A refers to... see how bad I am ? ) and I'll let you know my findings. My, lots of work!

[tggzzz]

... and have in mind that kid must be away as there is potential danger and the fact I'll do it in the kitchen

Personally, I wouldn't. Consider that cooking in a kitchen produces aerosols of whatever you are cooking. The droplets are small and hang in the air for a long time. These droplets will eventually stick to nearby surfaces.

When you look at the scope internals, you will see that many switches (e.g. vertical sensitivity and timebases) are exposed finger contacts. When they get dirty they can be carefully cleaned in such a way the fingers aren't damaged. And then there is the problem of films on sensitive front ends etc.

My attitude with my daughter was to encourage her to stick her head into things that I was doing. She could see me thinking about what might hurt me and then taking precautions to avoid problems. To give her a clue about electricity, I took her into the country and found an small moveable electric fence. After testing it myself, I told her to lightly touch the back of her fingers to the fence - and why not to grasp it or touch it with the inside of her grip.

Later on she became a solo glider pilot before she could start to learn to drive, and self-funded a 6 month trip to the antipodes between school and university. Exposing her to calculated dangers worked well.

And need to borrow a second scope when it's ripple time.

Start by using a multimeter on AC ranges.

[Malefoda]

Study the SM, really study it....pull the case off and get to the point where you know where things that are mentioned in the SM actually physically are. Take your time and become familiar with it's guts and mark test points if they aren't identified.

Well, in fact there is no choice, opened the beast and almost wanted to cry, that's no mere alarm clock! With no clue of what to look for that was useless. RTFM definitely, but at least I saw TPs are written down on PCBs.

Exposing her to calculated dangers worked well.

So is this how you call Brexit, calculated dangers?  just kidding!

[tggzzz]

Exposing her to calculated dangers worked well.

So is this how you call Brexit, calculated dangers?  just kidding!

Known and unacceptable dangers. But since this isn't a political forum, I'll say no more on that topic.

[Lorenzo_1]

1861-1 is a page number in the manual. Go to page 243 of the PDF file or thereabouts and you'll find it. Can't help you with SN question. Note that the Electrotanya manual specifies applicable numbers on it's title page.

[tggzzz]

Study the SM, really study it....pull the case off and get to the point where you know where things that are mentioned in the SM actually physically are. Take your time and become familiar with it's guts and mark test points if they aren't identified.

Well, in fact there is no choice, opened the beast and almost wanted to cry, that's no mere alarm clock! With no clue of what to look for that was useless. RTFM definitely, but at least I saw TPs are written down on PCBs.

Take it slowly, start with the section on faultfinding PSU problems. There's no point in looking elsewhere until all the power rails are correct.

[Malefoda]

Hello,

the most probable you predicted was right. I am amazed on how it managed to work with such supplies few days ago...
I need to change all the filter capacitors, 5 big caps with odd finger shape, need time to spend finding cheap and suitable ones.

[tggzzz]

the most probable you predicted was right. I am amazed on how it managed to work with such supplies few days ago...
I need to change all the filter capacitors, 5 big caps with odd finger shape, need time to spend finding cheap and suitable ones.

It can be difficult to remove those without damaging the PCB tracks. Some of the through-plate holes are used to connect different sections of tracks, as is the cap's can. Hence you should ensure that you add new bridging wires where necessary.

Caps with those leads are difficult and expensive to find. The usual technique is to use a modern capacitor, with similar capacitance, significantly higher voltage rating (to reduce the ESR), a high temperature rating and specified for SMPS operation (i.e not 50/100Hz!) for reliability. Then either create your own PCB for converting from 2-pin to 5-pin, or just bodge them in somehow.

See other posts for more details.

[Malefoda]

Ok thanks!
No more answer notifications but I just wanted to add that C1512 has already been changed, a tiny blue cap on which I can't read any brand. But they'll all go to the trash bin if too expensive, else that'll be the scope's place sadly.

[tggzzz]

Ok thanks!
No more answer notifications but I just wanted to add that C1512 has already been changed, a tiny blue cap on which I can't read any brand. But they'll all go to the trash bien is not too expensice, else that'll be the scope's place sadly.

Modern caps are surprisingly cheap.

It would be unnecessary to bin the scope - much better to advertise it on ebay stating its known problems. You would be surprised how much people will pay!

[WaveyDipole]

Ok thanks!
No more answer notifications but I just wanted to add that C1512 has already been changed, a tiny blue cap on which I can't read any brand. But they'll all go to the trash bien is not too expensice, else that'll be the scope's place sadly.

C1512 is across the 55v to 120v tx output via rectifier CR1511. Its stated capacity on the schematic is 550uF and I would expect it to be rated at least for 100v. Modern caps are fairly small, but I would not expect it to be tiny!

With the output voltages that low across the board, I would imagine that at least one of those smoothing capacitors (C1512,  C1513, C1542, C1552, C1562) is dragging the TX output down quite badly. What are you getting at 120v unreg?

I would check all capacitors on the atached which are marked in red. The one at the top left of the picture is under the metal shield. High voltages exist under this. Make sure evreything is powered off before removing that shield. Replace it imediately afterwards. Some of the indicated capacitor on the top of the PCB may be wet tantalum types. These tend to dry out an short over a long time. They might also be electrolytics so wowrth checking anyway. There will also be a handfull of blue bead types in the same general area between the big cans (which are underneath) and the metal shield and to the rear. These are dry tantalum capacitors and as someone has already mentioned, these should also be checked as short out when they fail.

As you have discovered, there is quite a lot going on underneath the hood and it can seem overwhelming. For now, just focus on the power supply section. If I might also point out, a number of parts protrude from the PCB at the sides and can easily be caught and damaged when removing or replacing the case so care needs to be taken to avoid damaging anything.

[Malefoda]

Hello gents,
as for caps I've chosen that series: http://uk.rs-online.com/web/p/condensateurs-aluminium/7441253/

For the new checks I've updated measurements with the 120V.


For on-boards highlighted caps I can only check for shorts (AFAIK with my DMM), none is shorted, they range from several k to 77 (C1220) depending on which cap in the circuit. My tantalum caps are red ones, many having like a rubber/hard-yellow-thing o-ring on leads. No Short is the only thing I can say.

Here is a picture of my Interface Board, dated 1971. (A big one, so I've linked the image instead of insterting it).
http://atsh.free.fr/temp/Tek465%20Interface%20Board.JPG

Right now I stick on saving a bit to afford caps, I want to keep it and sell my ugly Wavetek 9020.

[Malefoda]

Removed the caps today, all but easy.
Pads at the already replaced one are loose and I must admit I did lift one. Pictures were done to link ground where needed for there will be no more 4 legged caps.

I managed to get all the caps for 22€ shipped, bearable for me.

C1512, not tiny in fact (my english left to be desired sometimes, sorry) but at least smaller than OEM and even of lower capacitance! Looks like general purpose from BC.

[bd139]

Keep that wavetek one. You'll need it to fix the Tek one every time it goes wrong . If it's a derivative of the OS9020 they are not terrible scopes.

Those BC caps are nice.

With respect to the rail voltages, there are a couple of smaller electrolytic/tantalum ones on the interface board on the 55v rail after the regulator. I tend to desolder each of them in turn and see if the situation improves. Then the tants on the horizontal and vertical board. The entire scope's voltages are derived from the 55v rail if I remember correctly.

I'm praying that the EHT multiplier isn't dead or you're SOL without a donor scope and about 5 hours of work.

I've given up on old teks myself.  Have fixed several 4xx units.

[Malefoda]

Not very encouraging
The Wavetek is a rebranded Beckman Industrial 9020, never planned to have 2 scopes but if the Tek 465 is not reliable it's not going to stay.
Drum roll until I put new caps in. Hope it's not wasted money!

[bd139]

I've fixed worse ones believe me. Fingers crossed for you

[tggzzz]

Not very encouraging
The Wavetek is a rebranded Beckman Industrial 9020, never planned to have 2 scopes but if the Tek 465 is not reliable it's not going to stay.
Drum roll until I put new caps in. Hope it's not wasted money!

Don't be unnecessarily discouraged IMNSHO an analogue Tek beats most other analogue scopes.

OTOH, I'm not a fan of the DM44. While it works, it is complicated kludge due to of the technologies of the time. But, provided the knob works, they can be ignored.

[bd139]

Yes particularly my Hp1740A which has decided to stop sweeping this afternoon. Just after I sold the bloody rigol one too.

This is the analogue scope ownership experience. A good education however!

[Malefoda]

Seems owning oscilloscope is a hobby by itslef When I see parts cost, resell price of the 465 and the Wavetek I can get a fully working Tek 2236 and troubles away... and some money left! But then QED, oscilloscope itself becomes a hobby!

[tggzzz]

Yes particularly my Hp1740A which has decided to stop sweeping this afternoon.

The problem I had on mine was that a PCB track had been abraded.

On the timebase board the rotary timebase switch has a black plastic cover a couple of inches in diameter and with the "spear" from the front panel going through it. After removing the PCB, the black covers (one each side) can be removed after removing a springclip. Make sure you don't lose any of the gold finger connectors in the covers.

Examine the PCB tracks on the board where the edge of the covers rotates and touches them - and abrades them. The fix is simple: solder a single strand wire across the break, making sure no solder spreads onto the gold PCB switch contacts.