Author Topic: Tektronix 465M repair  (Read 2401 times)

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Offline andy3055

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Tektronix 465M repair
« 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.
 

Online tautech

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Re: Tektronix 465M repair
« Reply #1 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

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
You'll need to look up the transformer # and see if they have it:
https://www.sphere.bc.ca/test/tek-transformers.html
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #2 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.
 

Offline andy3055

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Re: Tektronix 465M repair
« Reply #3 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
« Last Edit: September 20, 2019, 05:40:56 am by andy3055 »
 

Offline andy3055

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Re: Tektronix 465M repair
« Reply #4 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 :-\
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #5 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.
 

Online tautech

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Re: Tektronix 465M repair
« Reply #6 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/
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #7 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.
 

Offline jdragoset

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Re: Tektronix 465M repair
« Reply #8 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.)
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #9 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!
 

Offline jdragoset

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Re: Tektronix 465M repair
« Reply #10 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
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #11 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.
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #12 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
 

Offline james_s

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Re: Tektronix 465M repair
« Reply #13 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.
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #14 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?
 

Offline james_s

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Re: Tektronix 465M repair
« Reply #15 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.
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #16 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.
 

Offline jdragoset

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Re: Tektronix 465M repair
« Reply #17 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.
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #18 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.
 

Offline james_s

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Re: Tektronix 465M repair
« Reply #19 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.
 
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Offline jdragoset

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Re: Tektronix 465M repair
« Reply #20 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. 
 
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Offline andy3055

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Re: Tektronix 465M repair
« Reply #21 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! ^-^
 

Offline andy3055

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Re: Tektronix 465M repair
« Reply #22 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.
 

Offline andy3055

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Re: Tektronix 465M repair
« Reply #23 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.
 

Offline andy3055

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Re: Tektronix 465M repair
« Reply #24 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.
« Last Edit: November 21, 2019, 06:47:02 am by andy3055 »
 


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