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A year ago I repaired a TDS 644A power supply.with overheated VR4 and VR5 snubbers and blown Q9 switch transistor. Q9 was replaced with an MJE8501 which was pencilled in on the schematic. The

Hello Daven9ooq, I will chuck in my 2 cents worth to help you. One of the previous posters suggested that you print out the schematics. I am going to adopt a Judge Judy attitude here. Have you printed

Hello, I'm interested in purchasing my first scope and looking for opinions on the TDS744A. I'm not interested in purchasing a Rigol/Siglent, etc - not that they are bad scopes, I've used Teks before

All I have ever seen draw in at the back. The air passes through the filter first before being delivered to the interior of the cabinet. Here is a bit of fan/blower trivia: A propellor fan needs

Did the TEK factory have the fan suck air in or blow it out the back? kevin

Steve, These optocouplers in the supply have a Small circle made with a dashed line surrounding an "M". It is not a "Motorola M", different from their LOGO. I'll bet these are made by MONSANTO. Thanks

Roy, Excellent information! I am not an I.E.E.E member. I'm pretty sure that they don't take old hot rodders and motorcycle mechanics turned electronics hobbyist as members. I have followed a lot of

Where I used to work, we used optocouplers to Isolate TELCO ring from our circuit and detect ring. We found that as the opto aged the ability of the photo device to see the emitter decreased. We

Chuck, Since I cannot tell what the original Zener or avalanche voltage was on this part, I am calling it a Zener. I understand that these diodes over a certain voltage (about 6V) are not truely

Glenn, I realize all of what you have very clearly stated. However, All of the diodes on this board are marked as "CRxxx". I am not a complete stranger as to how TEKTRONIX schematics have been marked

Hi All: I.E.E.E., NASA, and the U.S. Navy, et. al., have published papers citing the significant "failure" of these "critical" components in causing SMPSs not to operate. The authors are claiming that

Steve, As a life long EE, I would not have put up with that for a minute. Either the circuit would get redesigned, or the vendor of defective parts get banned. But, I have always been a bit of a

My point was most switching supplies have optocouplers that send signals in both directions. Typically, one will send a feedback signal from the low voltage side to the high voltage side, to regulate

A properly functioning colloquially named zener diode will have a forward conducting knee of 0.5-0.7 volts, and a reverse conducting knee at the published zener voltage. Any voltage below the

Chuck, He would change them 3 or 4 at a time. Now we see two or three over 5 or 6 units. The 6130C uses 22 (or so) and the OEM HP ones were unstable. HP got better, but at the time (1979) they broke

Steve, I have been repairing switching supplies since the mid 1980's, and I have yet to have to replace an optocoupler. Not one. That is very odd, given your statement. Perhaps, whatever a 6130 is, it

Chuck, If the opto-couplers are "HP" I'd have to argue with you. My boss (late '70's) at Opto Elec Div used to do the 6130C's and 6131C's and before he started he poured a little pile of couplers on

CRxx indicates "Crystal Rectifier" with a sequence number. Crystal Rectifiers are diodes. CR17 would be the seventeenth diode inserted into the schematic. Due to revisions and other reasons all the

Chuck, I am trying to learn and NOT be a bother to anyone.? I appreciate your help, cannot say that enough. ? You are correct on both 1 and 2.? See my response, sent before I read this message.?

Chuck, You are 100% correct about that optocoupler. I pulled that component out of circuit and it tests good. Don't know why I even trust "in circuit" tests? Moving back to your "million dollar hint".