Always suspect old carbon composition resistors. I see wild value changes in them all the time, and as Uwe says, even in those in safe protected storage.
----- Original Message ----- To: "Multiple recipients of list CHIPDIR-L" <[email protected]> Sent: Monday, September 19, 2005 3:59 AM > Are those resistors carbon-composite types from the 1960's? > > In that case I wouldn't be so sure that you can eliminate them. We had > couple of those in a student lab I was teaching. Every once in a > while we found 5.6kohm devices with roughly 200ohms and/or vice versa. > > These were unused resistors which were still in their original > package, not exposed to anything which might be considered harmful for > a resistor during the 30+ years of their shelf life... > > > Uwe. > > > >> Recently, Somebody Somewhere wrote these words >>> > These are venerable transistors in a TO5 can. The board is a Siemens >>> > part, which they have made 'obsolete' without replacing it. This is >>> > hardly surprising, as the devices are batch dated '6940' >>> > >>> > The board is basically a set of interconnected discrete bipolar >>> > logic gates, with some intermittent fault. I can find huge gain >>> > mismatches, and I want to replace the low gain devices. >>> >>> I have to ask why you want to do that. Classically, those circuits >>> were designed so that the low gain devices work just fine. Excessive >>> gain can cause it's own problems. ?? > >> I have this obsolete board from the Electricity Supply Board's Turlogh >> (pronounced Turlock) Hill plant which has an intermittent fault. It has >> diodes, resistors, and SST117s. I can eliminate the diodes, the >> resistors, and so am left looking at the transistors. > >> When these boards classically went intermittent, what was the issue? No >> capacitors here, beyond a few pF. There's 100pF across one resistor. >> The caps don't leak. I can check and exercise them with Analogue >> Signature Analysis. > >>> >>> Also, it appears that the SST11x series of JFETs is a clone of the >>> J11x series from a different time than the SST117. I think it's >>> unlikely that a logic board would have been made from JFETs in 1969. > >> That's another 'red herring' correctly categorised, then :-) >> -- > >> With best Regards, > > >> Declan Moriarty. > > -- > Author: Uwe Zimmermann > INET: [EMAIL PROTECTED] > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > -- Author: Syd H. Levine INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
