4 Sep
2011
4 Sep
'11
2:06 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 04 September 2011 20:22
To: cctalk at classiccmp.org
Subject: Re: RQDX3 DEVOFFLINE Problems
> Oops, didn't check that properly! I really should have checked the
> full function of the chip.
>
> Pin 1 of the 158 is connected to a signal that is definitely wrong in
> that it is Low when it should be High. Tracking this back it is
> looking like a failure in a DEC 8837 chip which is listed as a
"RECEIVER,
BUS,
HEX, UN".
Often DEC-numbered parts are selected versions of standard ICs with the
same number, bnd the parameter they're sleected for may not really matter
(!). Have you tried puting '8837' in one of the data sheet search engines
to
see what comes up. If the function and pinout looks
sane, it may be a
suitable
device.
Hw many pins does htis device have? What is the full functionality (or can
you
point me to an on-line copy of the printset so I can
look over the
schematic)?
In particualr, does this cjip have enable inputs, and are they used (that
is, not
tied to +5V/gnd as appropriate)? Yes, you really do
have to check
everything.
-tony
The PDF of the printset came from here:
http://bitsavers.org/pdf/dec/qbus/MP02259_RQDX3_schem_Oct85.pdf
Look at p12 for the M5098, the component that is not working is E1,
specifically pin 3 is high and pin 4 is high, but pin 1 is high and pin 2 is
low.
I checked the enable inputs too, pins 7 and 9, and they are both low, which
looks correct to me.
There seems to be a National Semiconductor chip with a similar designation
and description
(http://www.datasheetcatalog.org/datasheets/120/216865_DS.pdf), but that
does not seem to be made any more and I don't know what the equivalent is
(if any).
Someone has offered me a couple of 8837s, but if I can find a source of
equivalents I would prefer to buy those rather than use someone's spares.
Regards
Rob