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HP Forum Archive 08

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9100 question
Message #1 Posted by andy on 8 May 2002, 1:10 p.m.

I am trying to troubleshoot a semi-working 9100A. It can +,-,*,/ and the pi button works, but when you try to take exp(1) the CRT goes blank and never comes back with an answer. Interestingly, if you toggle th power switch, it sometimes re-powers with 2.7183 on the CRT.

Also, the trig functions do the same thing.

Any suggestions?



Re: 9100 question
Message #2 Posted by Tony Duell (UK) on 8 May 2002, 7:48 p.m.,
in response to message #1 by andy

It sounds like a problem with the main ROM assembly. You're not getting data from some locations, and the machine is locking up waiting for it (essentially). I had a similar problem on one of mu 9100Bs, but the machine didn't do anything (no display at all). Testing revealed no activity on the ROM data outputs. Msot likely one of the address driver transistors has failed. These are on the ROM PCB itself -- the 'middle' PCB in the assembly. Open up the case, remove the keyboard and card reader units. Unplug the PSU cable from the top of the left sideboard, undo the screws (9?) holding the processor chassis in place. Pull it forwards to free the I/O connector from the case, then flip it over (take care, there's still the mains cable for the switch linking the processor chassis to the rest of the machine). Take off the sideboards (3 screws each). then undo the 4 screws holding the ROM to the chassis (2 at the back, 2 at the front -- these screws come down from the top of the processor). Take off the complete ROM assemblu. The PCB across the back is the address decoder, those down the sides are the data sense amplifiers, while the ROM itself is in the middle. On that middle board you'll see a handful of transsitors. Check them all, at least for having good junctions. Take _great_ care soldering on this PCB -- if you damage the inter-layer vias, it can't be repaired (the track routing is how the data is actually stored in the ROM, so patching between components on the surface of th PCB won't help). Most likely one of the transistors (probably one of the TO5 (larger) ones is open-circuit. Replace it, but note that these transsitors are critical, and you'll have to experiment to find one that works. If that's not the problem, check the 512 diodes at the front of the ROM PCB (under the metal cover) and then suspect a fault on the address decoder PCB.

Re: 9100 question
Message #3 Posted by Ellis Easley on 9 May 2002, 10:06 p.m.,
in response to message #2 by Tony Duell (UK)

Tony, I tried counting the transistors in my 9100B but stopped at 600. BTW, how's that ascii-art schematic of the 9100 coming?!!!

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