That preamp board has 2 chips LM833 with 8 pins. i measured both Pins 4 (-13.5V) Pins 8 (14.00V) on both chips before it starting blowing fuses. Darn! gotta find that bad output transistor.
Ok. I've read it but thought that method was for transistor off of the board. I'll re-read.
thanks
Ok. I tried your testing method fromt his link (http://www.bcae1.com/ampfail.htm)on mosfet chips i have off the board and it works great. on the money. as a matter fact, these were the old mosfet chips i pulled from the amp cause i originally tested them and was not getting the results that are shown your page. That's why I puled them as i thought they were defective. turns out they are not. This is what is making me think there has to be a different way to test them on the board to determine a defective chip without having to take them out individually to test.
not sure why i'm not getting the same readings using your test method while on the board but I am when i test them off the board. I'm sure it has something to do with connecting power to the board.
any insight would be great.
i really appreciate your help.
thanks
not sure why i'm not getting the same readings using your test method while on the board but I am when i test them off the board. I'm sure it has something to do with connecting power to the board.
any insight would be great.
i really appreciate your help.
thanks
Read through this material and also did some more research on line. Seems that there is a short whenever the remote wire is plugged into B+. Hence fuse "pops". Which equals a shorted out mosfet chip(s).
I checked resistance (outer legs) on all chips and came up with below values:
Q7 = 4.92 MOhms
Q6 = 4.92 MOhms
Q9 = 4.92 MOhms
Q8 = 4.92 MOhms
Q206 = 4.88 MOhms
Q207 = 4.88 MOhms
Q204 = 4.92 MOhms
Q203 = 4.92 MOhms
Q103 = 71.8 Ohms *
Q104 = 91.6 Ohms
Q107 = 1.3 Ohms *
Q106 = 21.0 Ohms *
U1 = 13.4 KOhms
U2 = 1.063 KOhms
CR5 = .2 Ohms *
CR4 = .2 Ohms *
Based on these numbers Q103 - Q107 (Audio Output) are no good and U1,U2, CR5, and CR4 (Power Output) are also no good - due to low resistance between the resistors terminals. All 8 chips need to be removed/replaced and amp retested with 10 amp fuse only.
*Tested all chips for continuity (rule out for shorts) and these were the only ones that had continuity when testing outer legs.
Would my assessment to remove the 8 chips above be correct?
Thanks,
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Pull Q107 and recheck the transistors in that channel.
You can't tell if integrated circuits (the regulators) are good by continuity tests unless you have a known good sample or unless it's shorted/badly leaking.
The rectifiers are good. The section I suggested that you read covers the rectifier issue.
You can't tell if integrated circuits (the regulators) are good by continuity tests unless you have a known good sample or unless it's shorted/badly leaking.
The rectifiers are good. The section I suggested that you read covers the rectifier issue.
Thanks Perry,
Pulled Q107 and replaced with new one. New resistance measuring results:
Q103 = 72 Ohms *
Q104 = 91.8 Ohms *
Q107 = 4.84 MOhms
Q106 = 4.84 MOhms
*Getting beep when checking these for continuity. Since I'm already here I'm going to replace these two.
*Should they not also measure 4.84 MOhms?
Pulled Q107 and replaced with new one. New resistance measuring results:
Q103 = 72 Ohms *
Q104 = 91.8 Ohms *
Q107 = 4.84 MOhms
Q106 = 4.84 MOhms
*Getting beep when checking these for continuity. Since I'm already here I'm going to replace these two.
*Should they not also measure 4.84 MOhms?
Thanks Perry,
Pulled Q107 and replaced with new one. New resistance measuring results:
Q103 = 72 Ohms *
Q104 = 91.8 Ohms *
Q107 = 4.84 MOhms
Q106 = 4.84 MOhms
*Getting beep when checking these for continuity. Since I'm already here I'm going to replace these two.
*Should they not also measure 4.84 MOhms?
Pulled Q107 and replaced with new one. New resistance measuring results:
Q103 = 72 Ohms *
Q104 = 91.8 Ohms *
Q107 = 4.84 MOhms
Q106 = 4.84 MOhms
*Getting beep when checking these for continuity. Since I'm already here I'm going to replace these two.
*Should they not also measure 4.84 MOhms?
Changed Q103/Q104 and measurements did not change. Put the amp on bench test with a 10 amp fuse and no more popping fuses. 
However, I get no audio out of either of the channels, not even faint audio as before.
Preamp board has 2 chips "LM833" with 8 pins. I measured both Pins 4 (-14.00V) Pins 8 (14.00V) on both chips.
Not sure where to go from here. ?????
However, I get no audio out of either of the channels, not even faint audio as before.
Preamp board has 2 chips "LM833" with 8 pins. I measured both Pins 4 (-14.00V) Pins 8 (14.00V) on both chips.
Not sure where to go from here. ?????
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