Tektronix 2465B vertical shift problem

[ppppenguin]

My wonderful 2465B 'scope has a problem. If I adjust the vertical shift controls on channels 1 and 2 the trace distorts as it's moved down the screen. It's fine at the top of the screen. Ch3 & 4 are OK. The Ch2 output is OK.

Looking at the schematic all the channels and shift controls are fed into a hybrid chip. U400 is a very black box that takes all the vertical signals and feeds the main vertical amplifier.

Unless there's an obvious power supply fault around U400 then I need the unobtainable hybrid

https://www.tek.com/oscilloscope/2465b-m...465b-2467b
Page is "Channel switch and output ampliferis 2465B, sheet 6."

This article may offer some salvation: http://worldphaco.com/uploads/TEKTRONIX_...AKAGE..pdf
There could be excessive common mode DC on the differential Ch1 and 2 signals feeding U400 caused by some kind of fault that's common to both channels.

[Nick]

You need the TekScopes forum:

https://groups.yahoo.com/neo/groups/TekScopes/info

I bought a spare U800 (155-0241-02) and U400 (155-0236-00 or -09) from QService some years ago, just in case.

They are available, but you will have to spend about USD 100 on each.

[ppppenguin]

Nick, the Yahoo forum has long gone. I've just joined its replacement here: https://groups.io/g/TekScopes/topics

My first post is awaiting moderator approval.

Looking around it seems that U400 can be repalced with teh same part from any 24xx scope. I have a 2465 sitting around with an intermittent fault that could be a donor. Am I right in thinking the part can replaced simply by undoing the nuts and lifting it out of a socket? Taking out the main board looks like a big job.

[ppppenguin]

I have three Tek 24xx series scope.

The 2465B (400MHz) which is my everyday scope. Bought secondhand some years ago, probably about 10 years ago for about £800. This replaced...

An original 2465 (300MHz) which I bought secondhand for £2000 c1989. This was a superb investment for my then new business and was in daily use until I got the 2465B. It incresingly suffered from annoying intermittents that cause the Ch1 trace to jitter up and down. Never managed to track down the problem which was the main reason for getting the 2465B when it was offered at a good price.

A 2445A with Opt 05 (TV) whose origin I'm not sure of. It has calibration RAM failure but otherwise works fine. I've never really used it.

I've just "borrowed" the U400 from my 2465 and it has solved the problem. Changing it is dead easy. Undo 4 nuts, lift the old part off, reverse the process to install new part. Not sure about correct tightness for the nuts so I used common sense and also did them up in sequence as you would a car cylinder head.

The best deal I saw on a U400 is this one: https://www.ebay.co.uk/itm/TESTED-WORKING-Tektronix-Channel-Switch-U400-155-0236-00-2400-Oscilloscope-IC-2/282767530666?epid=1810061189&hash=item41d6421aaa:g:rDwAAOSwxixaLXW7:rk:2:pf:0

I'm not actually registered on ebay but if I decide to get it then I'll need to register. Also need to factor in VAT and customs handling but it's a business expense so I get the VAT back. The worry with importing a part is if it turns out to be faulty.

[Terry]

The worry with importing  a part is if it turns out to be faulty.

Well, the site does state '30-day returns', Jeffrey.

Quite a site - 2,800 items. I only looked at the first page but it is a very broad selection.

[ppppenguin]

Terry, you're right about their site. There's a lot of unusual laser, microwave, vacuum and heaven knows what stuff there.

[Nick]

Nick, the Yahoo forum has long gone. I've just joined its replacement here: https://groups.io/g/TekScopes/topics

Ah! Shows how long ago I looked at it. I use groups.io as the archive for the NEONIXIE-L group - one of their strengths is that they can import an entire Yahoo! group, membership lists and all.

Not sure that they have a files section though - one advantage of Google Groups is that it's integrated from a security standpoint with Google Drive.

Looking around it seems that U400 can be repalced with teh same part from any 24xx scope.

True.

Am I right in thinking the part can replaced simply by undoing the nuts and lifting it out of a socket? Taking out the main board looks like a big job.

True.

[ppppenguin]

The tekscopes group still haven't approved my first post, several days after making it.

[Cardigan]

I'm not actually registered on ebay but if I decide to get it then I'll need to register. Also need to factor in VAT and customs handling but it's a business expense so I get the VAT back. The worry with importing  a part is if it turns out to be faulty.

I would strongly recommend QService in Rhodes. As it's in the EU. no customs charges.

[ppppenguin]

Thanks for the suggestion. £93 with free postage.
https://www.qservice.tv/vpasp/shopexd.asp?id=1895

My registration on the tekscopes forum has finally been approved: https://groups.io/g/TekScopes/topic/2465...0,27485131

Chuck Harris makes some good suggestions but since Ch3/4 are OK his comments about the vertical deflection plate connections are surely not correct.