|Re: My 97 is mad at me!---Tony: Vss,Vgg RESULTS|
Message #20 Posted by W. Bruce Maguire II on 29 Oct 2001, 8:17 p.m.,
in response to message #19 by Tony Duell (UK)
Tony (and other HW gurus following my plight):
What are you using as the PSU? The 'classic charger' is the 3 pin one
used on the HP35, 45, 55, 65, 67, 70, 80 right? The constant voltage part of
that should be 4.1V or thereabouts. If you are getting 5.1V then either the
charger is defective, it's been modified, or your voltmeter is inaccurate. It's
worth finding out which at this point.
Sorry for the confusion. I did _not_ mean to say a 97 wall-wart. I _did_ mean
the classic charger. Yes, the constant-voltage side is supposed
to be about 4.0 VDC, but this one is actually 5.1 VDC. In order to see if the
DVM is reading 25% high, I checked several AA and AAA cells. I got 1.43 VDC to
1.49 VDC. I don't think the meter is in error; I think the supply puts out 5.1
VDC. Unfortunately, I don't have a scope at home, so I can't verify the signal
by looking at the waveform.
That is a regulated PSU, but the current rating (and smoothing
capacitor size) is a bit small for a topcat machine. The supply might not be
stable and smooth on-load. Vss and Vgg look reasonable, but if the PSU input is
not smooth then they might not be smooth either. I really would try to get a
stable 5V supply (an old PC PSU with a suitable dummy load to keep it happy if
you can't get anything else ?) and see what happens then.
I'll work on verifying that the results are the same with a better power supply.
Assuming you have a stable input supply, and Vss/Vgg look fine, then
you really need a 'scope or logic probe/analyser for the next tests (CPU clock
signals, ISA, Sync lines). One trivial thing... TEXT DELETED.