Im working on a PPI Art A600 which had failed outputs on the left channel. I replaced all outputs in BOTH channels with 2n6488 and 2n6491 as the originals were BDT81/BDT82 and NLA. There is 1 twist as there is an extra 91 on one channel, and an extra 88 in the other channel. I believe I did this correctly as I went over it 3 times before soldering. I did not replace any drivers which are C2344 and A1011 being controlled by MPSA06. All these transistors are testing out well off the PCB.
The amp powers, and gently plays through speaker terminals to my HoneyTone, but as soon as I hook up an actual 4-ohm load the amp clamps on my power supply and there is no sound.
Another symptom is the amp can only be powered for about 40 seconds before the outputs get too warm for idling. Also amperage draw starts at 1.3A, and over that 40 seconds rises to un-expected levels. I pulled power at 2.75A as it was starting to really take off.
All VR pots are set to full CCW. There is no voltage across several emitters I've tested.
The left channel has 1.4vDC on it while the right has +-0.1vDC. Theres a DC reference pot but it can only get the left channel down to about 1.1vDC.
Am I missing something? I checked multiple components and nothing is popping out at me.
The amp powers, and gently plays through speaker terminals to my HoneyTone, but as soon as I hook up an actual 4-ohm load the amp clamps on my power supply and there is no sound.
Another symptom is the amp can only be powered for about 40 seconds before the outputs get too warm for idling. Also amperage draw starts at 1.3A, and over that 40 seconds rises to un-expected levels. I pulled power at 2.75A as it was starting to really take off.
All VR pots are set to full CCW. There is no voltage across several emitters I've tested.
The left channel has 1.4vDC on it while the right has +-0.1vDC. Theres a DC reference pot but it can only get the left channel down to about 1.1vDC.
Am I missing something? I checked multiple components and nothing is popping out at me.
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There's a conflict between no voltage across the emitter resistors and the outputs heating up. Re-check the voltage across the resistors.
If you install shunts on the 2-pin headers, does that prevent the outputs from heating up?
Were all of the outputs heating up or were you possibly assuming that the regulator transistors were output transtors?
If you install shunts on the 2-pin headers, does that prevent the outputs from heating up?
Were all of the outputs heating up or were you possibly assuming that the regulator transistors were output transtors?
OK I re-checked and looks like there IS 0.003vDC across emitters.
When I install jumpers, the outputs do not heat up. 0.000vDC across emitters, and current draw drops to 0.8A. With the exception of the voltage regulators, output stay cool like this.
Still 1.4vDC across left speaker terminal.
When I install jumpers, the outputs do not heat up. 0.000vDC across emitters, and current draw drops to 0.8A. With the exception of the voltage regulators, output stay cool like this.
Still 1.4vDC across left speaker terminal.
Well, I fixed the speaker terminal vDC and I probably fixed the whole amp as well. I sucked and re-soldered the larger transistors located on the fragile driver boards and vDC vanished on left terminal, well as the DC across emitters. I checked another PPI amp and this one in particular had bad solder connections on those little fragile boards.
I also noticed one set of emitter resistors were measuring 7~9ohms when they should have been 0.68ohms. So before I test any further; need to order more parts. 32x Emitter resistors to be exact.
Thank you
I also noticed one set of emitter resistors were measuring 7~9ohms when they should have been 0.68ohms. So before I test any further; need to order more parts. 32x Emitter resistors to be exact.
Thank you