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Electronics => Repair => Topic started by: andy3055 on September 17, 2019, 08:48:53 pm

Title: Tektronix 465M repair
Post by: andy3055 on September 17, 2019, 08:48:53 pm
Does any member know of a source for parts for a 465M? I may need the the voltage multiplier and/or the HV transformer. The reason is that a fuse in the HV transformer drive circuit keeps blowing. I have seen many old threads on the subject and none of the nearby parts as mentioned therein checked to be faulty.
I also must mention that it happened due to my leaving it on overnight on a hot day in the summer! Therefore my thinking is that one of these have shorted due to heat.
If any member knows how I could check these for failure, that will be helpful too.
Thanks in advance.
Title: Re: Tektronix 465M repair
Post by: tautech on September 19, 2019, 10:01:45 am
Welcome to the forum.

Best solution might be a parts mule.
The EHT and PDA areas of a CRO are under lots of stress and it's not uncommon for them to fail as the components age.
This has helped me over the years:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf (http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf)

Sphere has a good selection of scope parts but it seems they are sold out of multipliers:
https://www.sphere.bc.ca/test/tek-parts/tekparts5.html (https://www.sphere.bc.ca/test/tek-parts/tekparts5.html)
You'll need to look up the transformer # and see if they have it:
https://www.sphere.bc.ca/test/tek-transformers.html (https://www.sphere.bc.ca/test/tek-transformers.html)
Title: Re: Tektronix 465M repair
Post by: andy3055 on September 20, 2019, 05:33:34 am
Thanks for the reply.

Yes, I tried that source but it does not look like he has the correct parts. Transformer is not available as he mentioned. But Walter quoted for a HV multiplier which has the correct part number but looking at the image on their site, I realize that it is not the correct item. My scope has a HV "unit" that has the HV multiplier and a host of other components in one package-U550. It has 12 connections including the HV line. What Walter has is a standard 4 connection pkg.

I just started removing some of the connections so that it is isolated from the HV transformer. I want to power up tomorrow and see if it will still blow the fuse F558. If the 90 volt supply is alive, I can conclude that the transformer is good and the multiplier is the culprit.

Please see attached.

Any help is much appreciated.
Title: Re: Tektronix 465M repair
Post by: andy3055 on September 20, 2019, 05:39:14 am
These guys have a good image but the part is not available unfortunately:

https://www.qservice.eu/shopexd.asp?id=1388&bc=no (https://www.qservice.eu/shopexd.asp?id=1388&bc=no)
Title: Re: Tektronix 465M repair
Post by: andy3055 on September 23, 2019, 09:20:34 pm
I sent the images to Walter and he has confirmed what he has is indeed the same thing! So, I have ordered it today and waiting hopefully. Shipping from Canada to US is killing though :-\
Title: Re: Tektronix 465M repair
Post by: andy3055 on September 28, 2019, 03:54:10 am
The replacement Tripler came in but the result is the same as the old part. All low voltages are good until the tripler's HV input connection is soldered in, at which point, the same fuse F 558 blows. I thought it may be the CRT itself but disconnecting the EHT lead still does not resolve the issue. Removing the CRT base socket has no effect either. Since the only time the fuse blows is when pin 10 of the HV transformer is connected to the tripler's HV input even with the EHT plug disconnected, my guess is that the EHT transformer is drawing a heavy current on the primary when this connection is made.

Unfortunately, I have no way to confirm this as a replacement EHT transformer is not available. So, sadly, I may have to give up on this. If any members have any ideas, I will be glad to hear them.

Thanks.
Title: Re: Tektronix 465M repair
Post by: tautech on September 28, 2019, 04:14:11 am
Doesn't make sense if you think about it.
How can a 5mA load trip the primary side fuse ?

Can you measure the voltage on pin 10 of the HV transformer ?

Might be some tips in this thread including rolling your own multiplier:
https://www.eevblog.com/forum/repair/tektronix-465/ (https://www.eevblog.com/forum/repair/tektronix-465/)
Title: Re: Tektronix 465M repair
Post by: andy3055 on September 28, 2019, 04:28:56 am
Agreed, it does not make sense. Especially when 2 triplers act the same way unless both are faulty in the same way (the EHT section of each of them). That is why I suspected the EHT connection to the CRT. But like I mentioned, removing that did not do any good! I will have to get hold of a high voltage probe to check it as the voltage is around 2.5 kV.

I saw that thread you have posted. I am trying to get hold of a tripler from a TV or a tube type PC monitor so that I can hook it up and do another test.

I will attach the schematic for whatever it is worth.
Title: Re: Tektronix 465M repair
Post by: jdragoset on September 30, 2019, 09:35:48 pm
One has to wonder why so many PC connections for a HV multiplier.
with the muliplier off the board connect the ground and HV from the transformer and see if the fuse blows.
One of those other wires must connect to an on-board failed component (cap, diode, etc.)
Title: Re: Tektronix 465M repair
Post by: andy3055 on September 30, 2019, 11:02:39 pm
Thanks for the reply.

The multiplier is in the same module (U550) with the other HV parts. However, the EHT section is only 3 connections-input, ground and the EHT lead (please see schematic in my earlier post-U550). So, if I disconnect just the input lead from the HV transformer (pin 10) to the multiplier (Pin11) the fuse will not blow (while all other voltages are spot-on). This is the reason I suspected the EHT section of the U550. But the replacement unit I got does the same thing. Either both of them have failed the same way (No 100% guaranty that the replacement is new) or that part of the transformer winding is bad in my opinion.

The only way to eliminate the transformer is to feed the HV pin 10 to a separate tripler while the rest is connected. I have to find a known good tripler to do that. Now, it is a question of if it is worthwhile doing all that with a scope of this vintage with no spares available anywhere!
Title: Re: Tektronix 465M repair
Post by: jdragoset on October 01, 2019, 12:22:56 pm
Here are Ebay items for diodes and caps used for 2215 4X HV multiplier :

10pcs 2CL20KV 30mA High Voltage Diode Rectifier HF Tesla Coil
JB99T 20mA 20KV Rectifier High Voltage Diode 20pcs
US Stock 12pcs 2CL71 8KV 5mA 100nS High Voltage Diode HV Rectifier HF Tesla Coil
US Stock 10pcs Ceramic Disc Capacitors 1000pf 1nf 0.001uf 102 15000V 15KV

Cost is minimal and a single diode and cap can be used to rectify pin 10 output for DC 1X measurement.

The prototype was used to verify the rest of the scope operation.
Potting was done with 3M Scotchcast Resin 4
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 01, 2019, 03:54:47 pm
Thanks for the info. I am in the midst of re-arranging my office room where I do my repair work. I will definitely give this a trial.
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 15, 2019, 02:40:27 am
Here are Ebay items for diodes and caps used for 2215 4X HV multiplier :

10pcs 2CL20KV 30mA High Voltage Diode Rectifier HF Tesla Coil
JB99T 20mA 20KV Rectifier High Voltage Diode 20pcs
US Stock 12pcs 2CL71 8KV 5mA 100nS High Voltage Diode HV Rectifier HF Tesla Coil
US Stock 10pcs Ceramic Disc Capacitors 1000pf 1nf 0.001uf 102 15000V 15KV

Cost is minimal and a single diode and cap can be used to rectify pin 10 output for DC 1X measurement.

The prototype was used to verify the rest of the scope operation.
Potting was done with 3M Scotchcast Resin 4

jdragoset,

When you did this did you power it up before potting it for testing by any chance? Or did you pot it first? I was wondering if it would arc all over if you did not.

Thanks
Title: Re: Tektronix 465M repair
Post by: james_s on October 15, 2019, 03:06:50 am
Given the tight layout it will probably arc. You should be able to test it using a much lower voltage from a signal generator though to verify it is wired up correctly.
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 15, 2019, 03:26:35 am
Given the tight layout it will probably arc. You should be able to test it using a much lower voltage from a signal generator though to verify it is wired up correctly.

Thanks for the reply. What would happen if it is fed with something like 24 volts AC from a wall wart? Will it not work at that low frequency?
Title: Re: Tektronix 465M repair
Post by: james_s on October 15, 2019, 05:03:35 am
It won't be able to deliver much current but it ought to work to some degree.
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 15, 2019, 06:18:46 am
It won't be able to deliver much current but it ought to work to some degree.

As long as I can measure a safe voltage, I will know if it is configured and works or not.

Thanks.
Title: Re: Tektronix 465M repair
Post by: jdragoset on October 15, 2019, 02:08:33 pm
The final was potted before powering, figuring it would have arced, given the tight spacing.
The prototype was powered up as seen below.
This was only a 2215 with 8 kv anode voltage.
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 15, 2019, 05:20:55 pm
The final was potted before powering, figuring it would have arced, given the tight spacing.
The prototype was powered up as seen below.
This was only a 2215 with 8 kv anode voltage.

Amazing! Thanks. I believe I have to deal with almost double that voltage. The manual does not say exactly what the EHT voltage is.
Title: Re: Tektronix 465M repair
Post by: james_s on October 15, 2019, 07:56:13 pm
I think with a little care you should have no trouble at all, it's a simple enough circuit. Try it with low voltage AC from a transformer and as long as you get higher voltages out at the correct polarity and nothing is getting hot I'd say you can be reasonably confident it will work after potting.
Title: Re: Tektronix 465M repair
Post by: jdragoset on October 15, 2019, 09:47:07 pm
If the EHT multiplier is indeed only 3X, the AC from T 550, pin 10 may be 4 or 5 kv, so use appropriate ratings for caps and diodes.
This could be the reason for the bad transformer reputation.
I did sub the final diodes (much smaller than the Ukraine military diodes) into the prototype for testing. 
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 16, 2019, 12:29:38 am
I think with a little care you should have no trouble at all, it's a simple enough circuit. Try it with low voltage AC from a transformer and as long as you get higher voltages out at the correct polarity and nothing is getting hot I'd say you can be reasonably confident it will work after potting.

Thanks, you give me hope! ^-^
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 16, 2019, 12:37:39 am
If the EHT multiplier is indeed only 3X, the AC from T 550, pin 10 may be 4 or 5 kv, so use appropriate ratings for caps and diodes.
This could be the reason for the bad transformer reputation.
I did sub the final diodes (much smaller than the Ukraine military diodes) into the prototype for testing.

Thanks. Good advise. You are correct. The diagram says it is a x3 multiplier. Since pin 9 of the transformer is at -2 Kv , pin 10 is definitely around 4 or 5 Kv. I am going to take this very slow and be 10x more careful!

Thanks for the support.
Title: Re: Tektronix 465M repair
Post by: andy3055 on October 24, 2019, 05:19:49 am
Just found my HV probe from 30 years back! It measures only Dc up to 45 Kv!!! Hooked up a single HV diode to the end of it and checked the pin 10 of the transformer. It has close to 4Kv. This is a probe with an on-board meter (Kaise SK-9000). It is so tiny it could be not that accurate. So, most likely, it is 4Kv. At least the transformer seems to be good.

Ordered some HV diodes and caps to give it a go. No telling when that stuff will get here! Will update as it goes.

Thanks to everyone so far.
Title: Re: Tektronix 465M repair
Post by: andy3055 on November 21, 2019, 06:43:17 am
At last I have some encouraging news!

Here are the original views, partial HV/EHT supply schematic and my test setup. Some more images in the next post.
Title: Re: Tektronix 465M repair
Post by: andy3055 on November 21, 2019, 07:06:28 am
Trace and 95 Volt supply (as steady as it can be!) and 13 kV DC on my old DC EHT probe. I am glad I had this probe which I had forgotten about all this time. It has 2 ranges 30 and 45 kV DC.

Now the issue I have is that how to package this setup considering that only this section of the U 550 HV block is bad and I am still using the old block that has the rest of the HV supply to the cathode, focus etc. I could pack these components separate and mount it separate from that U 550 block but that means I will have 2 "boxes" in there. The other thing to do is to recreate the rest of this also and package all together as in the original U 550.

My thought is to try using SMD type caps since they have 6kV caps that are very small compared to the disc ceramics. I already have the diodes that are quite small. If any members can throw some ideas, it will be much appreciated.

Thanks in advance.
Title: Re: Tektronix 465M repair
Post by: tautech on November 21, 2019, 08:08:34 am
I think the 2 box solution is acceptable.
jdragoset showed how he did it earlier in this thread and Gapsus used 2 boxes too in the thread I linked earlier:
https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083 (https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083)

By using a plastic jiffy box and potting it you have options on where to place it ....within reason.
Title: Re: Tektronix 465M repair
Post by: andy3055 on November 21, 2019, 05:15:46 pm
I think the 2 box solution is acceptable.
jdragoset showed how he did it earlier in this thread and Gapsus used 2 boxes too in the thread I linked earlier:
https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083 (https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083)

By using a plastic jiffy box and potting it you have options on where to place it ....within reason.

Thanks tautech, that is true. Sometimes I think I should stay away from trying to do everything as "original" and make it easy on myself. But the challenge is hard to resist  8)

Certainly, physical sizes of parts have shrunk so much today. So, how did Tek make such a compact unit with all those components some 30+ or more years back, when there were no parts like today? Apart from the EHT tripler section, it contains a bunch of caps, diodes and resistors for the rest of the HV circuitry. I am amazed!

Another note: I did not have to use too many diodes to get to 13 kV. Only 4 diodes and 4 caps even though I hooked up 6 of each to begin with that gives about 18 kV. The schematic does not indicate what the EHT is even though it clearly says it is a x3 multiplier. I decided to stay at just 13 kV based on a 465 schematic where it indicates the anode voltage as 14-16 kV. Considering the age of this 465M, 13 kV should be a safe bet I think where I still have good intensity and focus.

Sadly, the replacement U 550 unit I got also has the same identical problem as the unit that was in the scope, which was hard to believe. It cost me more than US$ 100.00 by the time I had it in my hands. That was all down the drain to say the least.
Title: Re: Tektronix 465M repair
Post by: james_s on November 24, 2019, 07:45:33 am
It's vacuum potted in epoxy so the parts are all crammed in there in a way that would flash over instantly if operated in air. The potted HeNe laser power supplies are constructed similarly, notice the HV capacitors are practically touching with the diodes zig-zagging between them. https://www.repairfaq.org/sam/lgn60xry.jpg (https://www.repairfaq.org/sam/lgn60xry.jpg)
Title: Re: Tektronix 465M repair
Post by: andy3055 on November 24, 2019, 04:21:01 pm
Thanks, James. So, as I understand, by potting the parts provides the option to bring them close together as the potting compound acts as insulation strong enough to prevent arching. That makes sense as some of the potting compounds have dielectric strengths as high as several kV per mm!

I was thinking of using some SMD caps that are rated at 4-6kV. Do you think that is a viable option? I know I still have to pot the whole thing anyway. I am also looking for some one part potting compound so that I can avoid air bubbles that happens when mixing 2 part compounds. There are also those that come in pouches where one can simply break the seal between the compounds and mix so that air bubbles will not form. It is nice if I can find something that does not harden like rock so that it leaves the option to dissect it later if necessary. Any recommendations on such stuff?

Thanks for any input from any member.
Title: Re: Tektronix 465M repair
Post by: james_s on November 24, 2019, 05:53:04 pm
I don't know, I've never tried the surface mount parts. Seems like it ought to work fine, I'm not sure if it would offer advantages over through through hole.

Vacuum potting need not be anything fancy, you don't need to pull a hard vacuum, you just need enough to draw the air out. One of those hand pumps meant for bleeding brake systems and testing automotive vacuum actuators and valves should do the job. You do have to be careful pulling even a modest vacuum on containers as the force of the atmospheric pressure gets to be immense however I've used glass jars without imploding one yet, I place them inside a plastic bucket for safety.
Title: Re: Tektronix 465M repair
Post by: andy3055 on November 24, 2019, 07:55:16 pm
Thanks, James. Good points.
Title: Re: Tektronix 465M repair
Post by: 2N3055 on November 24, 2019, 10:06:45 pm
How about Corona Dope?
Title: Re: Tektronix 465M repair
Post by: jdragoset on November 24, 2019, 10:41:38 pm
Andy,
You could try hot glue and test the results.
It is easy to melt at 275-300 degrees and would be easy to remove with a heat gun.
I would not expect operating temperature to be high enough to melt in service.
I'm not sure of the dielectric strength, but would expect it to be quite high.
I would also think a carefully laid out 3-D architecture could eliminate high adjacent voltage differences.
Title: Re: Tektronix 465M repair
Post by: james_s on November 24, 2019, 10:46:55 pm
Hot glue is not great for HV stuff, I've tried it in the past.

I would just use epoxy. Even if you don't want to use a vacuum chamber you can get pretty good results by using a thin epoxy like the stuff meant for laminating fiberglass. I believe many epoxy resins will also thin if you heat them, although they will also cure faster.
Title: Re: Tektronix 465M repair
Post by: andy3055 on November 25, 2019, 07:14:28 am
Thanks for all the suggestions. I am still looking around but not decided yet on any one thing. Meanwhile, I am away from home baby sitting my 4 year old grand daughter which is paramount now after retirement! So the scope has to wait. The good thing is, it gives me more time to think :)

Will post back once I have a concrete plan.

Thanks and have a great Thanksgiving!
Title: Re: Tektronix 465M repair
Post by: tautech on November 25, 2019, 07:25:59 am
You don't want to consider anything else but a good potting compound, one with low viscosity, low shrinkage and good dielectric strength. Consult the data sheets for working time after mixing and temperature sensitivity before it cures as you may be able to warm it so to lower viscosity to help prevent air voids.
It ain't rocket science if you take care with product selection.

Title: Re: Tektronix 465M repair
Post by: andy3055 on November 25, 2019, 07:29:45 am
Thanks, tautech. I do want to get something that gives the most time for sure.
Title: Re: Tektronix 465M repair
Post by: andy3055 on December 16, 2019, 03:46:07 am
Update:

I have tested with 20kV diodes and 6kV caps and it seems to be working well with just 4 diodes and 4 caps at 13kV on the anode. One question remains still about the resistor at the output. I have tried various values like 820R, 330k, 470k, etc. with no difference. I have not tried 1M yet as I don't seem to have a good quality piece on hand. Is there any way to find out the best value since there seems no info available on this particular tripler from anyone who has reverse-engineered one yet. Since the rest of the HV stuff in the old unit is still in circuit and in use, I do not want to destroy it trying to drill/cut/heat to find what is there on the EHT output lead.

Any response will be much appreciated.

Thanks.
Title: Re: Tektronix 465M repair
Post by: james_s on December 17, 2019, 03:13:18 am
The resistor may just be there to protect the diodes in the event of a short circuit. If the value makes no difference I wouldn't worry about it too much. If your new multiplier does ever fail or you find other shortcomings, you know how to make a new one.
Title: Re: Tektronix 465M repair
Post by: andy3055 on December 17, 2019, 03:36:52 am
Thanks, James. Would you use a lower value such as 820R or go with a higher value like 1M or so?
Title: Re: Tektronix 465M repair
Post by: tautech on December 17, 2019, 04:27:20 am
Would you use a lower value such as 820R or go with a higher value like 1M or so?
Do the sums with the voltages involved to limit the current to less than Imax of the diodes.
Title: Re: Tektronix 465M repair
Post by: james_s on December 17, 2019, 05:15:28 am
Also use several lower value resistors in series instead of one high value resistor so as to limit the voltage across each one.
Title: Re: Tektronix 465M repair
Post by: andy3055 on December 17, 2019, 06:43:09 am
Good advise. Thanks to you both.
Title: Re: Tektronix 465M repair
Post by: m3vuv on December 17, 2019, 06:57:58 am
could you not use hv diodes from a microwave oven?
Title: Re: Tektronix 465M repair
Post by: m3vuv on December 17, 2019, 07:01:56 am
for potting compound ive used stuff called copon hycoat 60,used to use it doing repairs on hp gas pipelines for the cathodic protection,was 2 pack about as runny as thick cream,as regards insulation it was good to 4kv per mm
Title: Re: Tektronix 465M repair
Post by: andy3055 on December 17, 2019, 07:29:36 am
could you not use hv diodes from a microwave oven?

Those are too big in physical size. There are very much smaller (about 3 mm diameter x  8 mm L) 20 kV diodes that are pretty cheap on eBay.

Something like these: https://www.ebay.com/itm/8-pcs-2CLG-20KV-20mA-High-Voltage-Diode-HV-Rectifier-Tesla-Ham/273101370267?hash=item3f961c339b:g:ApMAAOxyE-dRzJsp (https://www.ebay.com/itm/8-pcs-2CLG-20KV-20mA-High-Voltage-Diode-HV-Rectifier-Tesla-Ham/273101370267?hash=item3f961c339b:g:ApMAAOxyE-dRzJsp)
Title: Re: Tektronix 465M repair
Post by: andy3055 on December 17, 2019, 07:30:48 am
for potting compound ive used stuff called copon hycoat 60,used to use it doing repairs on hp gas pipelines for the cathodic protection,was 2 pack about as runny as thick cream,as regards insulation it was good to 4kv per mm

Thanks for the info on the potting compound.
Title: Re: Tektronix 465M repair
Post by: tautech on December 17, 2019, 08:29:56 am
As mentioned before, you don't want to venture outside what is the appropriate potting compound for this job.
Not too hard or the chance of shrinkage could ruin the circuit albeit unlikely with passives daisy chained or too high viscosity so to minimize the chance of voids and with good dielectric strength.

Pay the bucks for a good product and sleep at night.
A quick hunt in Mouser for Encapsulating and potting compounds finds this one that should be fine for your needs:
https://www.mouser.com/ProductDetail/MG-Chemicals/832B-375ML?qs=sGAEpiMZZMvJqaFk9BIiv6jhjM0Pk6Jz0ZBekZO8Zms%3D (https://www.mouser.com/ProductDetail/MG-Chemicals/832B-375ML?qs=sGAEpiMZZMvJqaFk9BIiv6jhjM0Pk6Jz0ZBekZO8Zms%3D)
Title: Re: Tektronix 465M repair
Post by: andy3055 on December 17, 2019, 06:13:09 pm
Thanks, tautech.