|
|
Post by paradisecs on Oct 5, 2018 23:06:12 GMT
Recapped pre-amp and driver boards, new bias pots (cermet trimmers 100hm), new resistors (4 100FP, 2 820s) new Q15/25 & Q16/26 outputs, new C5146 moved to emitter of Q5116. New caps for C65/66 and C67,68,69.
Powered on with dimm bulb (no smoke, no shorts).
I don't get any voltages when testing bias using test points.
If I test voltages across transistors Q15/16 to Q25/26 base to base, on the left side I get between .7 and .8 volts min-max depending on pot position.
Right side I get nothing. Tried multiple pots. I've pulled the driver transistors out and re-tested and they appear fine.
I checked for voltage at all the lytics on the driver board and they are all outputting power.
Could this be one of the smaller transistors giving me a problem?
I've been using the SHP Amp Book as a guide for doing this but maybe I've missed something simple. I'll look again at the troubleshooting section about checking voltages based on the schematics later to see if maybe there is a bad cap.
Any thoughts what could be the problem?
Stephen
|
|
|
|
Post by Ron Rich on Oct 6, 2018 2:49:31 GMT
Stephen,
Transistor, or thirmister bias circuit ? Did you see the "Errors known in printed material" in our FAQ's section ?
Ron Rich
|
|
|
|
Post by paradisecs on Oct 6, 2018 14:25:56 GMT
Transistor bias. And yes I checked for printed errors and made necessary adjustments to those errors.
MStephen
|
|
|
|
Post by Ron Rich on Oct 6, 2018 16:42:50 GMT
Stephen,
OK--are the transistors good--all the sandblock resistors at spec. all drivers good and correct, as well as the pre-drivers ?
Ron Rich
|
|
|
|
Post by paradisecs on Oct 6, 2018 19:36:20 GMT
I'll get back to you on this weekend. I need to read up on the circuits so I use the correct terms. Plus, I'm waiting on a Film Cap that I didn't like the looks of.
Stephen
|
|
|
|
Post by paradisecs on Oct 18, 2018 3:20:41 GMT
Finally got back to this. SHP3 with Transistor Bias. I didn't realize that I had a SHP3 with Transistor Bias when I first started so I changed the bias pots to 100 Ohm cermet pots as recommended for the SHP3. Could that be why I'm getting the wrong bias voltage readings? I've run a diode test on the transistors and they seem to be fine. And since this is the transistor bias, what pots should be there? I think I'm reading the schematic as 3.3k but I'm not sure if that is correct.
Stephen
|
|
|
|
Post by Ron Rich on Oct 18, 2018 3:56:27 GMT
Stephen,
The 100 ohm pot should work--check the ones you removed-- are you using a dim bulb protector, in this test--you should be !!
Ron Rich
|
|
|
|
Post by paradisecs on Oct 19, 2018 17:51:10 GMT
I'm going slow on this while I try to learn the circuits and not just get it to work. While studying the schematics for the SHP3 from the Electronics Parts Cat Rev 3 I see a note on the bias circuit for R5160 & R5183 that says "connection on pot end is optional". What does that mean? How can it be optional?
Stephen
|
|
|
|
Post by Ron Rich on Oct 19, 2018 20:45:29 GMT
Stephen,
Look at how it's drawn--makes no difference if there, or not ---
Ron Rich
|
|
|
|
Post by robnyc on Oct 19, 2018 21:05:23 GMT
Stephan, there is something fundamentally wrong (and probably simple)going on here.
Do you have the correct +32 and-32 volts approx ? Verify those first.
Be sure to check for "fused out" traces on the driver board. If the unit flamed out at some point, that is common.
The bias range you state is way off and indicates too little B voltage at the finals. The bias pot swings current much wider and would not be at fault here.
RobNYC
|
|
|
|
Post by paradisecs on Oct 19, 2018 22:06:29 GMT
Thanks Rob. I'll check that. I found another change on this unit that doesn't match the 4 other SHP3s I have out. This particular unit has a 180 Ohm resistor coming from F02 to K05-13. It then has a diode between 13-14 of the trip relay. What are these for? I thought I read for the MIC but I can't where I thought I read it. I see them in the schematic but no mention of it being for optional equipment.
Stephen
|
|
|
|
Post by robnyc on Oct 19, 2018 22:20:26 GMT
When you see a diode used across a coil it is to slightly lengthen the time it remains pulled-in. When power is removed a coil "kicks back" a current, placing a diode across the coil causes that current to be recycled thus holding the coil a few milliseconds longer. The resistor is just to reduce the 32vdc to approx 24v for the relay. A second fuse which was absent on the first SHP's is to protect the power supply if something shorts the RVC motor line.
RobNYC
|
|
|
|
Post by paradisecs on Oct 19, 2018 22:45:09 GMT
Would you suggest adding these to the others SHPs then? I have the parts on hand I just wasn't sure why one had it and the other 3 didn't.
Stephen
|
|
|
|
Post by robnyc on Oct 20, 2018 1:03:13 GMT
Stephen, I don't know what you are seeing in those amps but, there --must-- be a fuse protecting the minus 32v supply as it feeds the relay and RVC motor line. There should be a 180 ohm resistor in series with the relay coil as well. The diode is optional. If you add one be sure to observe the polarity or it will cause a dead short.
Rob
|
|
|
|
Post by Ron Rich on Oct 20, 2018 2:39:13 GMT
Rob,
Iffin you look at the schematic-- the -32, nor the + 32 is fused in so far as amp operation goes--the main 3.2 A., fuse "covers" them (lol).
The 2 amp fuse was an added fuse that covers ONLY the RVC and mic power supply. Once again--the dropping resistor for the relay, and the diode have been in EVERY one of the thousand or so (probably more ?) of them I have seen-- ?? Ron Rich
|
|
