> -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Brent > Hilpert > Sent: 21 December 2015 10:12 > To: General Discussion: On-Topic and Off-Topic Posts > Subject: Re: VAX 4000-500 PSU Overload? > > The lighter-beige ones, some of which are wider, are likely caps, for example > the one beside the 34072 dual op amp looks to be a simple power decoupling > cap (across the IC power pins). > The reddish-brown units with 4-digit numbers are resistors: 3 sig figs & > zeroes multiplier, e.g. 1002 = 10,000 ohms, 1330 = 133 ohms, 1181 = 1180 > ohms. > The unmarked(?) 'redder' ones I expect are resistors, for example the one > above the "di" in "digital" looks like the feedback gain control resistor for the > op amp, although in other places that would make 4 resistors in parallel which > is unusual. > Resistors can generally be identified with a multimeter, if you can come up > with the same value when swapping the multimeter leads (polarity) and > stepping through the multimeter ohm ranges you've probably got the > resistance - making the multiple measurements to identify non-linear > responses to eliminate conductivity readings from semiconductor junctions. > > There looks to be two very similar networks around the two op amps in the > 34072. It wouldn't really be that difficult a board to RE, although it does look > like some poking around with a multimeter for continuity will be necessary to > track internal traces, but they look to be relatively limited in number.
Many thanks. My first measurements with a multimeter had suggested to me that the darker ones were the caps. Thanks for putting me right before getting too far with the reverse engineering. The multi-layers mean I won't necessarily know where there is a connection, I can deduce that there is one where a through hole appears to go nowhere, but who knows what other connections I might miss. Any idea what an A4H and a 2FH are? They must be some kind of transistor, but I am not sure what kind. Regards Rob
