Goodmorning guys:
I'm working with a RF500x2.
When it first came to me, it had
Almost all audio mosfets shorted out.
I de solder all of them and scoped signal
at the mosfets gate pads, and all signals
Looks good, I replaced all audio output
MOSFETs, but one channel shorted out
All its MOSFETs agai.
I desolder all the mosfets
From the bad channel and scoped the
Signal again and I see no problem with it.
Any suggestion ?
Thanks in advance
I'm working with a RF500x2.
When it first came to me, it had
Almost all audio mosfets shorted out.
I de solder all of them and scoped signal
at the mosfets gate pads, and all signals
Looks good, I replaced all audio output
MOSFETs, but one channel shorted out
All its MOSFETs agai.
I desolder all the mosfets
From the bad channel and scoped the
Signal again and I see no problem with it.
Any suggestion ?
Thanks in advance
If there is any significant fault in the drive circuit for these (and similar amps like the 800a2 or the 1100a2), it can destroy output transistors with no evidence of excessive current draw. This is because the output stage drive is switched on after the large bank of capacitors is fully charged. To force the output stage on at the application of the remote voltage, short Q11 from collector to emitter. This will allow you to use a current limiter to protect the output transistors if there is a problem.
Don't forget to set the bias pots fully counter-clockwise before applying power.
Don't forget to set the bias pots fully counter-clockwise before applying power.
Attachments
I shorted out the emitter and collector, set the bias counter clockwise
And use a 12 volts light bulb in series with the power supply.
Now there is audio at the speaker terminal, just a littler distort it or scratchy.
Does that mean I have a driver circuit issue ?
And use a 12 volts light bulb in series with the power supply.
Now there is audio at the speaker terminal, just a littler distort it or scratchy.
Does that mean I have a driver circuit issue ?
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You can expect it to be slightly distorted until you remove the jumper on the bias transistor and set the bias.
The 12v lamp as a limiter will offer no protection to the audio circuit in this amp unless you disable the turn-on delay with the jumper on Q11.
The 12v lamp as a limiter will offer no protection to the audio circuit in this amp unless you disable the turn-on delay with the jumper on Q11.
So now I need to remove the jumper and set the bias
while the amp is on?
By the way I only have 2 audio MOSFETs install for now,
One irf9640 and one irf640.
while the amp is on?
By the way I only have 2 audio MOSFETs install for now,
One irf9640 and one irf640.
Leave the jumper on Q11 until you're sure that the amp is 100%. If you have jumpers on the bias transistors, those will have to be removed before you set the bias. Before you can set the bias, all outputs have to be installed and clamped tightly to the heatsink.
I had no jumper on the bias transistor.
I'm going to troubleshoot the drive circuit
And see what I found.
I'm going to troubleshoot the drive circuit
And see what I found.
After doing a lot of troubleshooting in the drive circuit, and pulled out and test it almost every single component of it, I didnt fount any fault in it. Is there any other suggestion on what else to look for?
What's the problem right now?
It was blowing outputs but a limiter and the jumper on Q11 should have stopped that.
Are you having the same problem with both channels?
It was blowing outputs but a limiter and the jumper on Q11 should have stopped that.
Are you having the same problem with both channels?
I pulled out and checked everything in the drive circuit, and found no problem.
I them try to compare both channels and notice that the working channel bias does
Not change when the pot is adjusted all gate pads of the good channel are reading
14 volts regardless of the pot been adjusted., so I can not use it to compare, at this point
I'm a littler be stock.
I them try to compare both channels and notice that the working channel bias does
Not change when the pot is adjusted all gate pads of the good channel are reading
14 volts regardless of the pot been adjusted., so I can not use it to compare, at this point
I'm a littler be stock.
The original problem is, One channel is working, the other is shorting out the audio mosfets.
Now, After you suggested I jumped Q11 and set the bias counter clockwise, the channel looks Ok. it even have audio, Just a litter distort it.
I pulled out and checked everything in the drive circuit, and found no problem.
I them try to compare both channels and notice that the working channel bias does not change when the pot is adjusted. (all gate pads of the good channel are reading 14 volts regardless of the pot been adjusted), so I can not use it to do comparison. at this point I'm a littler lost.
Now, After you suggested I jumped Q11 and set the bias counter clockwise, the channel looks Ok. it even have audio, Just a litter distort it.
I pulled out and checked everything in the drive circuit, and found no problem.
I them try to compare both channels and notice that the working channel bias does not change when the pot is adjusted. (all gate pads of the good channel are reading 14 volts regardless of the pot been adjusted), so I can not use it to do comparison. at this point I'm a littler lost.
Are you sure that you have proper rail voltage?
Are all of the FETs in place in the good channel?
Are all of the FETs in place in the good channel?
BACK TO THIS AMP.
I FINALLY GOT THE AMP TO TURN ON WITHOUT BURNING MOSFETS.
BUT THE AUDIO IS VERY LOW. +- 15 VOLTS ARE PRESENT AT OP AMPS.
RAIL VOLTAGES ARE +- 169 VOLTS.
ANY IDEA?
I FINALLY GOT THE AMP TO TURN ON WITHOUT BURNING MOSFETS.
BUT THE AUDIO IS VERY LOW. +- 15 VOLTS ARE PRESENT AT OP AMPS.
RAIL VOLTAGES ARE +- 169 VOLTS.
ANY IDEA?
I'm Using the power supply negative as the reference ground to measure the rail
Voltage. And get +-69 volts, not 169 volts as mentioned before.
Voltage. And get +-69 volts, not 169 volts as mentioned before.
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