Hot ADCs on Tek 2232

[Tappy]

Hello.  I'm trying to repair my Tektronix 2322 scope.  I've successfully done the focus resistor fix, now I need to fix the other problem.  The two hybrid ADC modules (U2200 and U2201) both get very hot (75C) and this is causing gradual vertical drifting of both traces when in digital mode.  I've checked the +5v and -5v power rails, which are both spot on.

Has anyone out there got any ideas please?

[c4757p]

Are you sure that's what is causing the drift? If they're otherwise functioning, I don't see any reason to suspect that's a "problem". They most likely run cooler with the case closed (providing the proper ventilation paths), and I would expect them to be fairly high-power devices.

[Tappy]

thanks for the reply C4757p.  The drift shows up as random bits 'jumping' up to the next level, then all the bits will smooth out at that new, higher level, then the whole thing repeats.  The drift reverses if I cooler the modules with freezer spray.  I'm sure it never did this a year or so ago.  The chips of the modules are mounted on a large ceramic substrate (see photo), so maybe you're right that they are designed to get hot.  Thanks.
Credit for the photo goes to 'Wolfalex', another contributor on this forum: I hope he doesn't mind me using it here.