PPI PC2350 schematic or service manual?? - Page 2

Perry Babin · 5th November 2009, 08:03 PM

Perry Babin · 5th November 2009, 08:13 PM

If you need to do extensive troubleshooting and need to clamp the power semis, make some clamps like those in the attached image.

1moreamp · 5th November 2009, 09:44 PM

Nice clamp bars Perry.I think I will make a set like that. I use flat bars currently.
And you are correct this amp can not be tested like they did without having the power devices clamped down tightly. Just way too much juice in this amp for that sort of stuff without adequate sinking for the power transistor's.
Lucky they did not fail the lower rail supply pass elements along with the couple outputs... The lower rail supply pass transistors run hot at idle without a load, as I am sure you already know.

Also don't forget to measure the voltage drop across each emitter resistor set to check for poorly matched outputs due to replacement, which could cause uneven current sharing and output failure again after its all buttoned up...At this voltage level output matching is pretty much a must do for reliability reasons IMO&E...

soft4gsm · 6th November 2009, 10:10 PM

Today I have some success with this amplifier, but it seems strange, there is no quiescent bias current on power transistors. Somewhere I read, so this amp is class AB, but there are no voltage (or less than 1mv) drop on the 0.33ohm pairs resistors on emitters of the power transistors. It seems to be Class B, or I measured something wrong, because I do this in last moment before to go. The potentiometers are not touched by me. First one is for output “0” correction I thing, and the second one (R90) is for quiescent bias current. (I measure all this with no load, no input signal, and jumpers JP1 and JP2 open).
BTW, I removed all output power transistors (2SA1303 and 2SC3284) from the channel, that I think is bad, and then I applied the power from accu, and when I checked quickly output PSU voltages (+/- 56v), and no output DC voltage on outs, I connected audio in to 1KHz small sine signal, and both outputs was OK. (The channel without Power transistors still can work, if it is without load because Q20 and Q22 are still there.). After this test, I soldered 1 pair (PNP and NPN) power transistors to this channel, and checked again (without load of course) and again all was ok. So, I think Monday, when I connect All other transistors, all should be fine. Only I have to solve the problem with quiescent bias current and to check if all transistors in to the same rail are with similar parameters (but this can be done, if there is some quiescent bias current).
Total current drain from 12V power is 2 Amps (I think it should be 3 Amps.), but real voltage on my accu is 11.2v .

1moreamp · 7th November 2009, 02:20 AM

Perry can also verify this tidbit. The jumper located in the middle of each channel is to be jumper-ed so to bypass the thermal sensing so a steady bias setting can be achieved at room temperature and not have the temperature variance cause it to drift all over the place while you making final adjustments.

I myself am unsure of a factory bias point based on voltage drop across the emitter resistors, but I like to scope my amps to set this as to avoid crossover notch distortion, while staying within the Idle current draw spec from the amp maker, and keeping both channels as closely matched as possible.
Also be on the look out for the other adjustment pots in the channel that are for DC offset at the output.
These will also drift with bias a bit, so you will be going back and forth between these set points a bit until you find the sweet spot this amp likes to play at.

Been there and done this many times....

soft4gsm · 9th November 2009, 08:08 AM

So, This amplifier seems to be typical Calss B. No diodes like AB Class amps, Ube of the power transistors is 170mV --> no quiescent bias current , transistors are off. If someone have original (not repaired or tuned) and can measure quiescent bias current of power transistors, and if is more than 0 ---> please share with us

Perry Babin · 9th November 2009, 09:54 AM

This amp should be able to bias the outputs on.

What's the driver board supply voltage?

soft4gsm · 9th November 2009, 09:32 PM

Driver board is suppyed with +/-56v and power transistors with +/-58..59v.
Actualy, I can force to bias output stage with 6-7mA per transistor ot little bit more(with potentiometer R90 - in thermal compensation part), but the interesting thing for me is, so I newer touched both potentiometers , and the one channel, that I never repaired, have zero bias too. ( But I'm not sure if someone other is changed value of this potentiometers or not)
I'll try to put bias current on the output stage, but then I have to test the amp in High temperature mode... to see if the thermo compensation cirquit works well.
And one think more... I see one of the power transistors was replaced before... Now I replaced two more. I have measured h21e on all transistors (both rails), and see 10-15% difference between them. I know it's better to be as much as possible the same, but how much is enough?

TO-3 · 10th November 2009, 03:40 AM

Quote:

Originally Posted by 1moreamp

Perry can also verify this tidbit. The jumper located in the middle of each channel is to be jumper-ed so to bypass the thermal sensing so a steady bias setting can be achieved at room temperature and not have the temperature variance cause it to drift all over the place while you making final adjustments.

I myself am unsure of a factory bias point based on voltage drop across the emitter resistors, but I like to scope my amps to set this as to avoid crossover notch distortion, while staying within the Idle current draw spec from the amp maker, and keeping both channels as closely matched as possible.
Also be on the look out for the other adjustment pots in the channel that are for DC offset at the output.
These will also drift with bias a bit, so you will be going back and forth between these set points a bit until you find the sweet spot this amp likes to play at.

Been there and done this many times....

Hey all- Factory bias was set at .7V across the emitter resistors. You're method is probably better though.

As Perry mentioned, this amp can be biased without being attached to a HS, just keep an eye on the temperature of the voltage regulators on either side of the board. Under normal circumstances, these can be run for several minutes without being sunk.

Perry Babin · 10th November 2009, 04:52 AM

Are you sure the bias was 0.7v instead of 0.007v or 0.0007v?

1mv across the resistors should produce clean output across the spectrum.

If I said the bias could be set without having the amp clamped to the sink, I was wrong.

5th November 2009, 08:03 PM	#11
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	email me. babin_perry@yahoo.com __________________ Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing

9th November 2009, 09:54 AM	#17
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	This amp should be able to bias the outputs on. What's the driver board supply voltage? __________________ Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing

10th November 2009, 04:52 AM	#20
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Are you sure the bias was 0.7v instead of 0.007v or 0.0007v? 1mv across the resistors should produce clean output across the spectrum. If I said the bias could be set without having the amp clamped to the sink, I was wrong. __________________ Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing

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5th November 2009, 09:44 PM	#13
1moreamp diyAudio Member Join Date: Dec 2005 Location: Northern California	Nice clamp bars Perry.I think I will make a set like that. I use flat bars currently. And you are correct this amp can not be tested like they did without having the power devices clamped down tightly. Just way too much juice in this amp for that sort of stuff without adequate sinking for the power transistor's. Lucky they did not fail the lower rail supply pass elements along with the couple outputs... The lower rail supply pass transistors run hot at idle without a load, as I am sure you already know. Also don't forget to measure the voltage drop across each emitter resistor set to check for poorly matched outputs due to replacement, which could cause uneven current sharing and output failure again after its all buttoned up...At this voltage level output matching is pretty much a must do for reliability reasons IMO&E...

6th November 2009, 10:10 PM	#14
soft4gsm diyAudio Member Join Date: Sep 2005	Today I have some success with this amplifier, but it seems strange, there is no quiescent bias current on power transistors. Somewhere I read, so this amp is class AB, but there are no voltage (or less than 1mv) drop on the 0.33ohm pairs resistors on emitters of the power transistors. It seems to be Class B, or I measured something wrong, because I do this in last moment before to go. The potentiometers are not touched by me. First one is for output “0” correction I thing, and the second one (R90) is for quiescent bias current. (I measure all this with no load, no input signal, and jumpers JP1 and JP2 open). BTW, I removed all output power transistors (2SA1303 and 2SC3284) from the channel, that I think is bad, and then I applied the power from accu, and when I checked quickly output PSU voltages (+/- 56v), and no output DC voltage on outs, I connected audio in to 1KHz small sine signal, and both outputs was OK. (The channel without Power transistors still can work, if it is without load because Q20 and Q22 are still there.). After this test, I soldered 1 pair (PNP and NPN) power transistors to this channel, and checked again (without load of course) and again all was ok. So, I think Monday, when I connect All other transistors, all should be fine. Only I have to solve the problem with quiescent bias current and to check if all transistors in to the same rail are with similar parameters (but this can be done, if there is some quiescent bias current). Total current drain from 12V power is 2 Amps (I think it should be 3 Amps.), but real voltage on my accu is 11.2v .

7th November 2009, 02:20 AM	#15
1moreamp diyAudio Member Join Date: Dec 2005 Location: Northern California	Perry can also verify this tidbit. The jumper located in the middle of each channel is to be jumper-ed so to bypass the thermal sensing so a steady bias setting can be achieved at room temperature and not have the temperature variance cause it to drift all over the place while you making final adjustments. I myself am unsure of a factory bias point based on voltage drop across the emitter resistors, but I like to scope my amps to set this as to avoid crossover notch distortion, while staying within the Idle current draw spec from the amp maker, and keeping both channels as closely matched as possible. Also be on the look out for the other adjustment pots in the channel that are for DC offset at the output. These will also drift with bias a bit, so you will be going back and forth between these set points a bit until you find the sweet spot this amp likes to play at. Been there and done this many times....

9th November 2009, 08:08 AM	#16
soft4gsm diyAudio Member Join Date: Sep 2005	So, This amplifier seems to be typical Calss B. No diodes like AB Class amps, Ube of the power transistors is 170mV --> no quiescent bias current , transistors are off. If someone have original (not repaired or tuned) and can measure quiescent bias current of power transistors, and if is more than 0 ---> please share with us

9th November 2009, 09:32 PM	#18
soft4gsm diyAudio Member Join Date: Sep 2005	Driver board is suppyed with +/-56v and power transistors with +/-58..59v. Actualy, I can force to bias output stage with 6-7mA per transistor ot little bit more(with potentiometer R90 - in thermal compensation part), but the interesting thing for me is, so I newer touched both potentiometers , and the one channel, that I never repaired, have zero bias too. ( But I'm not sure if someone other is changed value of this potentiometers or not) I'll try to put bias current on the output stage, but then I have to test the amp in High temperature mode... to see if the thermo compensation cirquit works well. And one think more... I see one of the power transistors was replaced before... Now I replaced two more. I have measured h21e on all transistors (both rails), and see 10-15% difference between them. I know it's better to be as much as possible the same, but how much is enough?

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