HP 6632B @ BAD INT

[Ussovak]

Been reading eevblog post for a long time and everyone seems to have a solution for everything. This is great. Being my first post, I hope I can finally resolve my problem with a HP 6632B.

I bought the unit from ebay and when I received the unit, I powered it up and everything seemed good but I did not test every aspect. I turned the unit off for a couple of hours and when I turned the unit back on, I got nothing, - a completely blank display. I check ac power and of course good. I then turned the unit back off and then on, but this time the entire display was on - meaning every character was nice and bright. But the display just stayed that way until I turned the unit back off. Sometimes when the unit is power cycled, I get just a few characters on the display to show for a short period followed by the words "Bad Int". Then the display goes dark. One of the above mentioned is demonstrated with every power cycle but never consistent.

Not sure what "bad Int" means. This is my only clue that the unit may be attempting to tell me something. I can't find any reference to it in the service manual. This still does not explain the previous behavior - or does it?

Has anyone seen this before?

I checked the transformer wiring to confirm it's wired for 110 vac. This is correct. I also checked all of the rail and bias voltages. They are all correct.

Can anyone point me in the right direction?

[tppc]

Hi,
sounds like a problem on the interface assembly which is unfortunately not documented in the service manual.
Check the connections between front panel and interface assembly.

If you have an oscilloscope, you could check
- power suply to the processor
- logic levels around the processor
- Reset signal
- opto isolators...

Regards.

[Ussovak]

Thanks tppc

I kind of figured this issue was related to the A2 board somehow. But with really no documents regarding the A2 board itself, it looks hopeless. I'll do my best to check the obvious.

[Ussovak]

Appears the 40 Mhz oscillator on the A2 board is bad. I have +5v on the input and +5v on the output. The oscillator is a GS-165PHC. I compared this reading with another 6632b A2 unit (no one of mine) and theirs was +5v on the input and +2.5 on the output. I assume this means the crystal on my A2 board is shorted? Can anyone confirm this?

Now keep in mind I am measuring with a DMM which is probably a NO NO.