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Lost Ch 1 on my 465 scope


Ray, W4BYG <w4byg@...>
 

I accidentally touched the ground clip on my 465 Ch 1 probe to a "hot " AC-DC radio chassis. (I have an isolation transformer. Thought it was connected). It blew channel 1 out, but channel 2 and the rest of the scope's operations seem to be OK. I haven't yet started to trouble shoot the problem but tend to think it will be a major deal trying to fix channel one.

Has anyone gone thru this kind of an issue yet that they can offer any insight as to what gets damaged in a situation like this?

I bought this cope new in the seventies and have been the only user of it for all these years.

I have a spare 465 that is not working, which might serve for parts or modules as needed.

Your assistance and insight will be appreciated.
Ray, W4BYG


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Tom Lee
 

I have seen several scopes with blown inputs, although I acquired them in the dead state, with no knowledge of how they were killed.

That said, I'm sure it's not a big surprise that the input FETs do not fare well during big input overloads (the drain-gate diode tends to bite it, as it's used as a voltage clamp). Open up the 465, take a look around for obvious damage, and trace signals as they progress from the input forward. Don't be surprised if signal is lost pretty quickly. I've never seen wholesale destruction of a channel, so you may be lucky and find that the damage is confined to a small handful of components.

The 465 uses matched pairs in a can for the input source follower + bias. These were always somewhat rare, and they've only gotten rarer/more expensive over time. It's good that you have a parts queen. Hopefully that unit has good FETs, because I have a feeling that you'll be needing them.

Good luck!

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/12/2020 14:05, Ray, W4BYG wrote:
I accidentally touched the ground clip on my 465 Ch 1 probe to a "hot " AC-DC radio chassis. (I have an isolation transformer. Thought it was connected). It blew channel 1 out, but channel 2 and the rest of the scope's operations seem to be OK. I haven't yet started to trouble shoot the problem but tend to think it will be a major deal trying to fix channel one.

Has anyone gone thru this kind of an issue yet that they can offer any insight as to what gets damaged in a situation like this?

I bought this cope new in the seventies and have been the only user of it for all these years.

I have a spare 465 that is not working, which might serve for parts or modules as needed.

Your assistance and insight will be appreciated.
Ray, W4BYG


toby@...
 

On 2020-10-12 5:34 p.m., Tom Lee wrote:
...
The 465 uses matched pairs in a can for the input source follower +
bias. These were always somewhat rare, and they've only gotten
rarer/more expensive over time. It's good that you have a parts queen.
Hopefully that unit has good FETs, because I have a feeling that you'll
be needing them.
Not sure which type is in the 465, but Linear Systems does sell various
equivalent dual matched JFETs for types used in other Tek instruments
(specifically 603/604 XY's in my case) and they have been great to deal
with.

http://www.linearsystems.com/product.html

--Toby
(not affiliated, just customer)



Good luck!

--Tom


pdxareaid
 

I posted a reply yesterday, which I will try to duplicate. Yesterday, I also reported an inappropriate post.
Today I looked and MY post was gone and the inappropriate post remained. Later in the day the inappropriate post disappeared.
I don't know if i did something or a mistake was made and the wrong post removed. I did have a link to an ebay post
to demonstrate a part was still available. Maybe that is against the rules. I don't know. I got no feedback. I will not include that
info this time.

I had a similar 465B vertical channel, which was damaged by the previous owner. I found, by tracing a signal from the probe thru
the channel, that the dual can Tom Lee and others mentioned was indeed blown as well as a 16 pin spider like Tektronix IC differential amp.
At the time, a few years ago, both were available, one off, on ebay and elsewhere for about $25 each. I looked and the spider is still available on ebay.
I am not posting that link now. There are several versions of that spider, differing in the last 2 digits of the part number, which you may want to pay attention to
in terms of matching both channel 1 and 2 using either spare parts or parts you may purchase.
Good luck.


Tom Lee
 

I didn't check to see if my reply had also been a victim of collateral damage, but I'll reiterate that the 465B and the 465 are significantly different. The 465B does use a Tek custom IC (the "spider" thing) in the front end, but the 465 does not. The latter's vert. preamp is all discrete.

--Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/13/2020 14:02, pdxareaid wrote:
I posted a reply yesterday, which I will try to duplicate. Yesterday, I also reported an inappropriate post.
Today I looked and MY post was gone and the inappropriate post remained. Later in the day the inappropriate post disappeared.
I don't know if i did something or a mistake was made and the wrong post removed. I did have a link to an ebay post
to demonstrate a part was still available. Maybe that is against the rules. I don't know. I got no feedback. I will not include that
info this time.

I had a similar 465B vertical channel, which was damaged by the previous owner. I found, by tracing a signal from the probe thru
the channel, that the dual can Tom Lee and others mentioned was indeed blown as well as a 16 pin spider like Tektronix IC differential amp.
At the time, a few years ago, both were available, one off, on ebay and elsewhere for about $25 each. I looked and the spider is still available on ebay.
I am not posting that link now. There are several versions of that spider, differing in the last 2 digits of the part number, which you may want to pay attention to
in terms of matching both channel 1 and 2 using either spare parts or parts you may purchase.
Good luck.




pdxareaid
 

Thanks Tom,
I should have checked. Nevermind :-)


Tom Lee
 

Oh, no problem at all!

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/13/2020 14:51, pdxareaid wrote:
Thanks Tom,
I should have checked. Nevermind :-)




Tom Lee
 

The 465 doesn't have the Tek-special IC like the 465B has, so that makes it a bit easier/cheaper to repair. The B model is actually fairly different from the original (Tek skipped "A" and went straight to "B" because of the long list of cumulative changes they wanted to implement)

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/12/2020 17:13, pdxareaid wrote:
Years ago I acquired a 465B off craigslist from someone that blew one vertical channel, probably doing something similar to what happened to yours.
I did not check but I'm pretty sure the parts will be identical for 465 and 465B.
The dual can that Tom Lee mentions was blown as well as the 16 pin spider differential amp just after it in the path.
Having one channel good, I followed a signal back and swapped parts between good and bad channels to confirm my suspicions.
When I last looked, they could both be had off ebay for about $25 each, one off.

edit:
I took a quick look on ebay...spiders are still available. As I recall, there are several versions with differing part numbers in the trailing 2 digits...might want to match that exactly.
Just incase you find it bad.
example: https://www.ebay.com/itm/Tektronix-Custom-IC-Vertical-Amplifier-Part-No-155-0078-10/183764511426?epid=1210059427&hash=item2ac937eac2:g:OH4AAOSw2hhcgZ82