Tektronix 7603 with 7B53A and 7A26 plug ins

[Nick]

I think you've done infinitely better than most getting this far.

I can't see anything round U2126 that should damage it. Do you want to try mine? Of course there's always a risk attached to that sort of thing but that's life.
If you want to give it a go PM me your Address and I'll fish it out and put it in the Post. I assume there's just no Readout without it in, not that I use mine a lot, 'scope that is.

Indeed - 10/10 for persistence (!)

I don't know why this particular chip dies so often - some of the Tek custom ICs had over-heating issues - the infamous U800 in the 2465-series (155-0241-02) is probably the best known - possible failure mode?

Some folk have gone so far as to produce modern ASIC or FPGA replacements for one or two..., e.g. http://www.davmar.org/TE/Tek2465/lafay.html

[Refugee]

I am so sure that a new chip would cure it that I would not like to put a good one at risk in the post.
I will just keep looking.

[AlanBeckett]

OK. Let me know if you change your mind.

Alan

[Refugee]

What I will do for now is a calibration check and If my gear is not up to it I will borrow or buy a calibrator for this.
Then I can find it a home in my test gear rack.

[Nick]

Are you now happy that the 155-0021 is dead and that it died of natural causes, i.e. not due to still-extant some external condition?

[Refugee]

Before calibration I will check all the waveforms on it a little more thoroughly to confirm that there are no dodgy voltages on it and then I will be happy that it is indeed dead of natural causes.
There is pin 9 that as far as I can see is not used. It has -15 volts on it. Pin 8 is -15 volts power. They are either side of the end of the package as opposed to next to each other.
The other connected chips are doing what they should.
I will check the z axis amplifier to make sure it is not supposed to provide a pull up.

[AlanBeckett]

OK, let me know if you want anything else measuring.
I've put it away but it's easy to get out again.

Alan

[Nick]

I note that some folk have seen the diodes surrounding that chip also fail - are you happy that they're all good?

[Refugee]

Yes I will check all the connected components before I am finished with the diagnosis.

[Refugee]

I have now completed the diagnosis of the on screen display. During my final test to check for an open circuit pull up resistor on the Z axis amplifier board at the other end of the coax that connects to pin 10 of U2126 I found a twiddler fault and promptly fixed it.
   
   
Now the other twiddler problem is two panels are missing. These are the bottom blue one and the white finger guard that covers the power transistors at the back.
So do I go for silver for the side panels and wait for a frame with a smashed tube for replacement panels and the screws that hold them on?