24 Jul
2013
24 Jul
'13
3:58 a.m.
-----Oorspronkelijk bericht-----
Van: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
Namens Dave
Verzonden: woensdag 24 juli 2013 7:46
Aan: General Discussion: On-Topic and Off-Topic Posts
Onderwerp: Re: HP 9830A always turns on with blank display
an
________________________________
From: Tony Duell <ard at p850ug1.demon.co.uk>
To: cctalk at classiccmp.org
Sent: Saturday, July 20, 2013 2:03 PM
Subject: Re: HP 9830A always turns on with blank display
Right. My guesss is that it's the Init/ signal from the power supply
that is the root of the problem. Porbbly the I/O flag circuitry on the
I/O interface PCB is not being initialised or soemthing.
Check that 74121 on the PSU board and especially the 6.8uF capacitors
around it.
-tony
I will check this out, hopefully this weekend.? Out of curiosity, is there extender or some other way of probing these boards
while powered up?
By the way, does anybody know the number of the mating plugs to make a
cable
for the 9866A printer?? It looks like a 19-pin cannon
connector.? These
seem
expensive, so at least it would be nice to be
confident I'm seeking the
right
model.? Any info on plugs and cable would be welcome.
Many thanks,
Dave
Yes there are extender boards but those are extremely rare..
But you can run the PSU without most of the boards in place, it needs some
load but not all the boards.
If you remove the memory subsystem RAM and register boards you should have
space enough to measure the /Init signal.
But it is also available on the CPU control board, you have to measure the
5V and /Init signal together and look if the /Init signal has enough delay.
On the CPU control board you can find the /Init signals on U16 and U17 both
74H108 JK-flip-flop's, the reset input is connected to the /Init signal and
resets the Micro code PC at power on.
If you solder a small wire to it you should be able to connect an LA or
Scope to it.
In my experience the 74121 and 74123 have a high failure rate, but it's also
a good idea to check the ESR values of the surrounding cap's (tantalium and
elco's).
-Rik