0.22 ohm 2 watt are the resistor values you asked about, and I would replace all four just in case the other two may have opened up or been damaged also. You appear to have a blown channel. I suggest you remove and replace the 2N6487 and 2N6490 output devices and replace them when you replace the resistors. Also check those MPSA56 and MPSA06 transistors near those burnt resistors they will likley be leaking at 3 cents each I would replace them for good measure just to assure a complete rebuild of the channel.
This will likely not completely resolve your issues but its a start.
After that I am highly suspect of the ceramic SIP module in front of those burnt components. Perry Babin has a nice tutorial on his links about that module. I suggest you look it up to get a perspective on what your dealing with to start. They can be repaired in many cases. But if its badly damaged then a suitable replacement might be in order. They can be tough to come by nowadays.
I'm not sure what your reading in your last post but its possibly not relevant at this point. I would stick with the bad channel repairs first...
Your DC offset adjustments are those four gold painted pots located in the center of the board, The other gold paint pots one in each channel are your output bias adjustments, I would leave those alone for now. Replace the known bad components and then retest that bad channels DC offset and tech out the SIP module. Once all of that has been corrected then I would worry about making any final adjustments...
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Sooooo.... I ended up breaking off two of the IRFZ34N mosfets accidentally, bad part is they test good. Good part is I took the axe to the one that's different than the others and it measures way different than all of the others when doing the diode check on it so Im chalking that one up to being bad. I'm going to be on the back burner till around next weekend I would guess (waiting for parts and time off from work) Unless someone has any other ideas that I can test without powering the amp up. I would really like to know why my toroid voltage was so low. How do I test the toroid?
Thanks for all the help.
Thanks for all the help.
You said the low impedance led is on correct? Then that is my best guess as to why your voltage readings are too low. Please remove all ofthe blown devices in the bad channel, then test your voltages after all possible shorts have been removed. This power supply isn't going to operate properly till all defective/shorted devices are removed from circuit, it was designed that way, so your fighting a design feature the engineers placed there IMHO.
Perry is correct you only need a couple of the fets in the supply to turn the amp on, but you must have them on both sides of the amp so both primaries of the toroid have switched voltage to them. So you can move one of two of them around as long as you have them on both sides of the board so the circuit sees fets on both primaries. I test amps with only a single pair of fets in the supply one on each side of the board. I have a PCX-2125 here right now with only a single fet on each side of the board and it fires up just fine, and idles properly. They can get hot fast so again Perry is wise to warn you to mount the amp back on some sort of heat sink surface....
Got a little done tonight. I think you guys called it (sip card) I now have 886mv on right rear. Dc bias all the way down. Ac bias does nothing as far as amperage draw. On the plus side no more static through right rear, low impedance light is off, and the noise coming from toroid has stopped. Did a little testing on sip card and Q3 on Perry's sip card pic appears to be leaking. I will test further tomorrow.
Just for clarification the picture im refering to is this one:
I'll probably just do most testing against what I find on the good driver boards. I'm not at my bench right now but if somone could help me out on testing procedures (what to test how to test it) so I can read over it before I get off of work that would be great! Thanks!
I'll probably just do most testing against what I find on the good driver boards. I'm not at my bench right now but if somone could help me out on testing procedures (what to test how to test it) so I can read over it before I get off of work that would be great! Thanks!
That photo is some of the old reverse engineering work I and another close friend did along time ago. I posted it only so Perry and you could share a common reference to work with. He could point you using the photo and it would be easy for the both of you to follow.
The numbers are not PPI designation but what my colleague applied so we could both have a common reference to work with. I just wanted to clarify this info so you both would have some common frame of reference to work with.
The numbers are not PPI designation but what my colleague applied so we could both have a common reference to work with. I just wanted to clarify this info so you both would have some common frame of reference to work with.
Cool thank you Cecil. I went through the schematic and labeled it with the numbering from your picture for a faster reference for myself. I am new to electronic circuits and such so it helps me out a lot. It took me a while last night to get everything right but I finally got it figured out. I think. I'm hoping to get some testing done today.
Pin 7 is common ground and pin 13 is the tab of Q2 so your reading thru transistors to ground, not a single 10 k ohm resistor. Simple DC measurements may not yield reliable test data especially if they are thru semiconductors like your reading. I would stick to any two given points on the same device for comparison work. What your reading is thru a bunch of components all at the same time so bouncing readings may be the norm since it not straight line of sight static measurement thru a single device.
maybe Perry has some better incite on this also....
maybe Perry has some better incite on this also....
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