Electronics > Repair

Tek 2445A repair help

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Hi all,

I'm a lurker, but finally decided to get in the proverbial game.

I recently acquired a 2445A for a song.

I had to just about power wash the grime off of it, but it does power up and show a trace. I replaced the seized fan with new unit from Mouser that I had laying around. Part # AD0812HB-C73-LF
However, after about 2 minutes the trace and readout starts jittering a lot.

Here's a video of what I'm talking about:

I also noticed a buzzing or high speed clicking sound. Maybe an arcing sound?
I did the requisite voltage check at J119, and obviously there's a problem with the +15v going on.

Here are the results:

I used a couple references for ground in order to double check myself.

I have the 2445 and the 2465B manual. The board layouts are a bit different, but close. I'll keep looking for a 2445A specific manual.

Here is the 15v regulator circuit from the 2465B manual, a close approximation of what I'm dealing with.

Where to go from here?

I'll try to keep this on topic and post pictures to help others.




Looks the same as the in the service manual of the 2445a.
Check the voltages of U1260-317.

So, I tested the voltage regulator, and it looks good to me.

So, still open to suggestions. :)

Here is another video, better showing the symptoms it's experiencing:

I don't think turning channel 2 on had anything to do with it, as it happens after a bit of time with no probes attached. Just coincidence. Also, it will sometimes clear up for a bit, then go crazy again.

Also, you can here the crt buzzing and carrying on a little better in this video.

Thanks for any input,


Get the Tek scope troubleshooting pdf from this post:
There are some tips in it for troubleshooting the SMPS

--- Quote ---I also noticed a buzzing or high speed clicking sound. Maybe an arcing sound?
--- End quote ---
That symptom is described.  :)

Failing E-Caps?

The 317 readings, can you monitor them to see if they are stable?

Do you have another scope to monitor PSU rails for ripple and when it misbehaves?


Will read recommended repair manual tonight, so forgive anything that may overlap. Also, it's really annoying that a lot of these manuals are password protected, allowing print only. I have a great OCR program that would be awesome to make these searchable. Oh well

Have another scope on the way, but it's probably wasted too. lol I'm a glutton for punishment. I have 10 8640B's waiting in line, that need functional checks and gone through.

With the Vreg ruled out for the most part, it's output seems to be stable, I focused on where the +15 was coming from before it reaches the J119 header.
It looks like the DLY REF 1 headed from U2521 through U2620 (High Speed OpAmp).

This is the schematic I'm working with:

A quick check of supporting components in the path turned up a bad resistor, R2720. Bottom of the red circle. I replaced that, and things have improved. It still freaks out, just not as bad and it takes a bit longer. Even a blind squirrel gets a nut once in a while.

However, the sound is definitely coming from the back of the crt, so maybe all of this is moot, if that's garbage. Maybe a problem with HV side of things?

Again, any suggestions are welcome.



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