I have a punch 800.2 that I’m repairing. Board# 3083. It had the typical blown and shorted output 9640’s on both channels when I got it.
So I removed all output mosfets, gate resistors, and source resistors for both channels. Also replaced all the A06/a56 right channel drivers because one was shorted. And all the 100 ohm resistors in series with the source resistors for both channels.
Before I replaced the mosfets and source resistors I powered up the amp and it seemed to power up fine. It settled at around .8-.9 amps when on. I took rail measurements and secondary voltage and all seemed good. Nothing seemed hot.
I replaced all the mosfets and source resistors (which are from mouser, allied, and future),and powered up the amp to have it short out when it turns on after the built in delay.
So first I checked all fets for shorts and there are none. Checked all new source resistors for high resistance and they all look good. All driver resistors measure good.
Next I thought I’d see if one rail or the other is causing the short. I lifted all the 9640 source resistors on both channels and of course the amp powers up fine and draws about 1 to 1.1 amps after delay.
All measurements look good on the 640’s. G 54.8 v dc D 0.003 vdc S 57.3 vdc. Then I pulled the 640 source resistors for both channels and re-installed the 9640 source resistors thinking something is wrong with them. But, when I turned it on it powered up fine drawing 1-1.1 amps. Measurements of the 9640’s- G -54.6vdc S -.003 vdc D -57.6 vdc.
I’ve compared the tl494 and lm339 pin voltage measurements to a working 501x I have. They are all very similar except the regulated low voltage legs are higher in the 800.2 I’m assuming because it’s regulated control voltage is higher than the 501x by about 5 volts each way and it matches the legs.
So this is my problem, it has a short in both channels when all mosfets are sourcing rail voltage to the output but not each rail individually on both channels.
So I removed all output mosfets, gate resistors, and source resistors for both channels. Also replaced all the A06/a56 right channel drivers because one was shorted. And all the 100 ohm resistors in series with the source resistors for both channels.
Before I replaced the mosfets and source resistors I powered up the amp and it seemed to power up fine. It settled at around .8-.9 amps when on. I took rail measurements and secondary voltage and all seemed good. Nothing seemed hot.
I replaced all the mosfets and source resistors (which are from mouser, allied, and future),and powered up the amp to have it short out when it turns on after the built in delay.
So first I checked all fets for shorts and there are none. Checked all new source resistors for high resistance and they all look good. All driver resistors measure good.
Next I thought I’d see if one rail or the other is causing the short. I lifted all the 9640 source resistors on both channels and of course the amp powers up fine and draws about 1 to 1.1 amps after delay.
All measurements look good on the 640’s. G 54.8 v dc D 0.003 vdc S 57.3 vdc. Then I pulled the 640 source resistors for both channels and re-installed the 9640 source resistors thinking something is wrong with them. But, when I turned it on it powered up fine drawing 1-1.1 amps. Measurements of the 9640’s- G -54.6vdc S -.003 vdc D -57.6 vdc.
I’ve compared the tl494 and lm339 pin voltage measurements to a working 501x I have. They are all very similar except the regulated low voltage legs are higher in the 800.2 I’m assuming because it’s regulated control voltage is higher than the 501x by about 5 volts each way and it matches the legs.
So this is my problem, it has a short in both channels when all mosfets are sourcing rail voltage to the output but not each rail individually on both channels.
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Please break up the text.
Lifting the source resistors generally results in damage to the protection circuit.
The 100 and 39 ohm resistors are in parallel with the source resistors.
You can't use voltage for troubleshooting in the feedback loop when parts are missing from the loop.
Secondary voltage pins?
Lifting the source resistors generally results in damage to the protection circuit.
The 100 and 39 ohm resistors are in parallel with the source resistors.
You can't use voltage for troubleshooting in the feedback loop when parts are missing from the loop.
Secondary voltage pins?
I edited the post and broke it up.
I usually lift the rail voltage diode legs but I thought this way would be better and tell me more. I see it isn’t.
I should have said regulated low voltage instead of secondary voltage and legs instead of pins. There where a few legs of the lm339 that measured the same voltage as the regulated low voltage.
In the 800.2 it was 17 volts and in the 501x it was 10 volts. It was the same legs in both amps that I measured the regulated voltage on just different values. The 800.2 has 17 volts on these legs and the 501x had 10 volts on them.
So I will put the source resistors back in and just lift the diode legs to get it to power on and maybe look at it that way.
I usually lift the rail voltage diode legs but I thought this way would be better and tell me more. I see it isn’t.
I should have said regulated low voltage instead of secondary voltage and legs instead of pins. There where a few legs of the lm339 that measured the same voltage as the regulated low voltage.
In the 800.2 it was 17 volts and in the 501x it was 10 volts. It was the same legs in both amps that I measured the regulated voltage on just different values. The 800.2 has 17 volts on these legs and the 501x had 10 volts on them.
So I will put the source resistors back in and just lift the diode legs to get it to power on and maybe look at it that way.
Ok, I have all source resistors soldered back into the board. All components are in nothing is removed.
When I apply 12v to the remote the amp turns on for about 2-3 seconds draws .4 amps then jumps to 30 amps (max on my power supply) after the 2-3 second delay. I cut the remote off immediately so not to cause more damage.
I again checked all the new output mosfets for shorts between all 3 legs with my meter set to diode check and their are none. All the new source resistors measure .1 ohm. All the new gate resistors are measuring right around 51 ohms.
I did remove and replace r238,r338 47 ohm resistors and the r264 r364 39 ohm resistors. They tested within tolerance when I checked them out of the circuit but I replaced them anyway.
There was no change to the amp on power up. It still maxes out current draw after the turn on delay.
Any ideas on what to try next? I’m out of ideas.
When I apply 12v to the remote the amp turns on for about 2-3 seconds draws .4 amps then jumps to 30 amps (max on my power supply) after the 2-3 second delay. I cut the remote off immediately so not to cause more damage.
I again checked all the new output mosfets for shorts between all 3 legs with my meter set to diode check and their are none. All the new source resistors measure .1 ohm. All the new gate resistors are measuring right around 51 ohms.
I did remove and replace r238,r338 47 ohm resistors and the r264 r364 39 ohm resistors. They tested within tolerance when I checked them out of the circuit but I replaced them anyway.
There was no change to the amp on power up. It still maxes out current draw after the turn on delay.
Any ideas on what to try next? I’m out of ideas.
2 ohm, 100w is most commonly used. Use a dummy load if you have a 2 ohm.
Short Q11 in the power supply from collector to emitter with a jumper.
When you power the amp up, it will have no turn-on delay for the output stage and won't allow the caps to charge. The limiter will prevent excessive current draw. Both will protect the outputs.
Which channel is drawing excessive current?
Short Q11 in the power supply from collector to emitter with a jumper.
When you power the amp up, it will have no turn-on delay for the output stage and won't allow the caps to charge. The limiter will prevent excessive current draw. Both will protect the outputs.
Which channel is drawing excessive current?
If you're using woofers in individual chambers, you can wire them out of phase to limit the bass.
I used a bass song to test amps. It's difficult to supply power to large amps running at full power with a sine wave. With music, you can test up to and intermittently into clipping for long periods, much easier. It's easier on the dummy loads as well.
I used a bass song to test amps. It's difficult to supply power to large amps running at full power with a sine wave. With music, you can test up to and intermittently into clipping for long periods, much easier. It's easier on the dummy loads as well.
Ok I got my load resistors. I have a 100 watt 2 ohm resistor in the B+ line. I have jumped the collector and emmiter of q11.
When I turn on the remote for the amp the current draw of the amp jumps to 5 amps then settles to 3 amps and holds steady. The b+ load resistor is heating up.
When I place a dummy load (100 watt 2 ohm resistor) on the right channel and the current draw of the amp is still 3.0 amps. I left it hooked up for a couple minutes to be sure.
When I place a dummy load on the left channel the amps current draw is 3.0 amps. I also left it on this channel for a couple minutes.
There is no change in current draw with a dummy load on either channel.
When I turn on the remote for the amp the current draw of the amp jumps to 5 amps then settles to 3 amps and holds steady. The b+ load resistor is heating up.
When I place a dummy load (100 watt 2 ohm resistor) on the right channel and the current draw of the amp is still 3.0 amps. I left it hooked up for a couple minutes to be sure.
When I place a dummy load on the left channel the amps current draw is 3.0 amps. I also left it on this channel for a couple minutes.
There is no change in current draw with a dummy load on either channel.
The current limiting resistor is going to get hot. I should have told you to order the cylindrical wirewound ceramic but didn't think of it at the time. What kind did you order?
You need to clamp the MEHSA insulators to the heatsink to protect the semiconductors.
Measure the DC voltage across all of the source resistors. How many read above 0.000v DC?
You need to clamp the MEHSA insulators to the heatsink to protect the semiconductors.
Measure the DC voltage across all of the source resistors. How many read above 0.000v DC?
I got the aluminum case wire wound type.
The board is clamped in the case.
Left channel:
R240- .005 vdc
R242- .003 vdc
R244- .003 vdc
R246- .003 vdc
R247- .003 vdc
R266- -.003vdc
R268- -.003vdc
R270- -.003vdc
R272- -.003vdc
R274- -.003vdc
Right channel:
R340- .003vdc
R342- .002vdc
R344- .002vdc
R346- .002vdc
R347- .002vdc
R366- -.002vdc
R368- -.002vdc
R370- -.002vdc
R372- -.002vdc
R374- -.001vdc
The board is clamped in the case.
Left channel:
R240- .005 vdc
R242- .003 vdc
R244- .003 vdc
R246- .003 vdc
R247- .003 vdc
R266- -.003vdc
R268- -.003vdc
R270- -.003vdc
R272- -.003vdc
R274- -.003vdc
Right channel:
R340- .003vdc
R342- .002vdc
R344- .002vdc
R346- .002vdc
R347- .002vdc
R366- -.002vdc
R368- -.002vdc
R370- -.002vdc
R372- -.002vdc
R374- -.001vdc
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Those have to be mounted to a heatsink with thermal paste to work at rated power.
R240 shouldn't be out of line with the rest.
What is the regulated voltage from the LM3x7 regulators?
If you connect a jumper between the collector and emitter of the bias transistor, in each channel, does the voltage across the source resistors drop to 0.000v?
R240 shouldn't be out of line with the rest.
What is the regulated voltage from the LM3x7 regulators?
If you connect a jumper between the collector and emitter of the bias transistor, in each channel, does the voltage across the source resistors drop to 0.000v?
I have an aluminum plate I’m going to mount the resistor to I just haven’t done it yet.
The positive regulated voltage out of the regulator is 19.34 vdc.
The negative regulated voltage out of the regulator is -19.41 vdc
All source resistors in each channel measure 0.000 vdc across them when I jumper the collector and emitter of the bias transistor in each channel.
The positive regulated voltage out of the regulator is 19.34 vdc.
The negative regulated voltage out of the regulator is -19.41 vdc
All source resistors in each channel measure 0.000 vdc across them when I jumper the collector and emitter of the bias transistor in each channel.
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