RQDX3 DEVOFFLINE Problems

-----Original Message----- From: Rob Jarratt [mailto:robert.jarratt at ntlworld.com] Sent: 04 September 2011 22:07 To: 'General Discussion: On-Topic and Off-Topic Posts' Subject: RE: RQDX3 DEVOFFLINE Problems > -----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

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

check everything. 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

I checked the enable inputs too, pins 7 and 9, and they are both low,

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