HP-85A problems..dead CPU?

From: Chris Hoaglin <Chris_at_omtsalvage.com>
Date: Sun Aug 12 19:50:54 2001

I put my 85A back together today after fixing the power supply..Now it seems to be
DOA from a short circuit caused by a misaligned flexprint strip connecting the PSU
to the CPU board. The symptoms are:

The CRT works, but no characters are displayed.

Typing on the keyboard does not produce text either.

The chip on the left rear of the CPU board, just in front of the two flexprint
cables leading to the ROM drawer, gets rather hot almost immediately. None of
the other chips exhibit this heat problem. This chip is marked
"IMA8 0101 82055 SINGAPORE", and I believe it is the CPU because of the
connection to the ROM drawer. One of the pins on this chip is connected to one of
the traces on the flexprint involved in the short.

Questions:

Does anybody have a schematic for the 85?

If this is the CPU, what pins should I be looking at for the clock?

If the chip is shot, is there any way to get a replacement, or do I
have to cannibalize another 85?

  

                   mailto:Chris_at_omtsalvage.com
Received on Sun Aug 12 2001 - 19:50:54 BST