The polarity of the big cap 100/47 is fine. The issue on one channel seems to be that the B+ is not connected to the differential pair -- Diode D3 is open, so no B+ to Q1/Q2.
The diode changes ought to fix the one channel. Since there is symmetry in that 9.8 volts is present at all collectors/emitters of Q1/Q2 both channels, I assume that there is also a B+ failure on the right channel.
Will post the results later... wish me luck.
The diode changes ought to fix the one channel. Since there is symmetry in that 9.8 volts is present at all collectors/emitters of Q1/Q2 both channels, I assume that there is also a B+ failure on the right channel.
Will post the results later... wish me luck.
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Hi, This is my first reply/post so cut me some slack if I need it. Anyway, I have just repaired a PL400 and PL200 with upgrades. Take a look at Phase Linear PL400/700/Dual 500 Repair Procedures for some very good suggestions on bringing these amps on line without destroying a lot of parts. I had a similar issue (full power supply out) and it was due to a broken trace where the single sided board component had been pushed down thus breaking the trace on the other side (at the input differential amp). After doing the repairs I covered the entire circuit side with epoxy to prevent it happening again. I also added swage in turret terminals where the wires attach to make servicing a little easier. I also removed all of the transistors and matched them up for Hfe and ended up with output offsets < 10mV. I also replaced many of the transistors with parts that have much higher Hfe, bandwidth, Vce and dissipation ratings. The PL 200 will do about 300 into 8 Ohms and 150 into 4 Ohms (not CW)because it is supply & fuse limited. I was not happy with the single sided 400's PL14A board so I designed and had 10 made with double sided plated through holes, split ground planes and an optional current source instead of the 200K resistor. I also added the option of full complementary outputs (with one jumper) as well as TO220 drivers. I hope to try one of the boards out shortly. This would allow making a serious upgrade to the PL400. I would be glad to chat with anyone who is interested.
You won't get flamed from me....
I've managed to fix one channel. Diode D3 was open on the right channel. I replaced D3/D4/D9 on the left channel to no apparently no effect. They did not measure well.
I then found a broken trace on the left channel, from D3 to the 100K resistor leading to the 1K pair and Q3/Q4. This was a big deal.
It was no longer outputting 75 volts. It was at just 7 volts. I did replace Q1/Q2 with matched 2N2222, and wanted to make sure it was not that, so I put the old ones back in -- still 7 volts-- even with a transistor in backwards!
The contact of Q3 to ground was suspect, so I added a wire on top of the trace. The output now drops slowly to -8 volts. It seems silly at this connects the Q3 emitter to the 39K input resistor -- on route to ground. Not a well designed board, I'd say.
There are entire traces and pads missing on my board. Folding over component wires may not be the best option....
This is progress, as one channel is done.
I'm convinced that the problems are all in the traces. Q1/2/3/4 have been repaired so much, they have pads that lift -- BOTH channels.
I was considering making my own boards using the solder mask in the PL400 service manual, but that mask does not match my board! There are missing traces on my board! Or, I've gone blind.....
I would be *very* interested in one of your boards...
I've managed to fix one channel. Diode D3 was open on the right channel. I replaced D3/D4/D9 on the left channel to no apparently no effect. They did not measure well.
I then found a broken trace on the left channel, from D3 to the 100K resistor leading to the 1K pair and Q3/Q4. This was a big deal.
It was no longer outputting 75 volts. It was at just 7 volts. I did replace Q1/Q2 with matched 2N2222, and wanted to make sure it was not that, so I put the old ones back in -- still 7 volts-- even with a transistor in backwards!
The contact of Q3 to ground was suspect, so I added a wire on top of the trace. The output now drops slowly to -8 volts. It seems silly at this connects the Q3 emitter to the 39K input resistor -- on route to ground. Not a well designed board, I'd say.
There are entire traces and pads missing on my board. Folding over component wires may not be the best option....
This is progress, as one channel is done.
I'm convinced that the problems are all in the traces. Q1/2/3/4 have been repaired so much, they have pads that lift -- BOTH channels.
I was considering making my own boards using the solder mask in the PL400 service manual, but that mask does not match my board! There are missing traces on my board! Or, I've gone blind.....
I would be *very* interested in one of your boards...
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Here are some suggestions on transistor types for the driver board that seem to work well in Phase Linear amps (no warranty expressed or implied):
Input diff amp NPN's - ZTX694B, buy 10 or more & match Hfe's - this will give lower output offset voltages, assuming there is not another issue.
2nd PNP diff amp - ZTX796A, buy 10 or more & match Hfe's - this will also help give lower output offset voltages
NPN voltage amp & driver - MJE15032, add a heatsink
PNP driver - MJE15033, add a heat sink
All of these are typically higher gain (Hfe), bandwidth, power, Vce, etc.
For the TO3 output driver and the outputs themselves NPN - 2ST5949. Much higher & flatter Hfe than the MJ15024, a little more current, same Vce & power, and a 25 MHz Ft. And it is cheaper. This is how I measure 300W RMS on a PL200B - It will swing 140V PP @ 8 Ohms. On the PL200B I had to reduce the value of the small 270pF capacitors to 27pF on the TO220 drivers for stability because of the added band width of the outputs.
PNP complement - 2ST2121 if you are going complimentary.
It would be easier to email me for a schematic & board .JPG if you want.
I have also had meter's needles bent from full VCC outputs. An added diode and a couple of resistor changes on the meter PCB will stop that.
Good luck on the repairs.
Input diff amp NPN's - ZTX694B, buy 10 or more & match Hfe's - this will give lower output offset voltages, assuming there is not another issue.
2nd PNP diff amp - ZTX796A, buy 10 or more & match Hfe's - this will also help give lower output offset voltages
NPN voltage amp & driver - MJE15032, add a heatsink
PNP driver - MJE15033, add a heat sink
All of these are typically higher gain (Hfe), bandwidth, power, Vce, etc.
For the TO3 output driver and the outputs themselves NPN - 2ST5949. Much higher & flatter Hfe than the MJ15024, a little more current, same Vce & power, and a 25 MHz Ft. And it is cheaper. This is how I measure 300W RMS on a PL200B - It will swing 140V PP @ 8 Ohms. On the PL200B I had to reduce the value of the small 270pF capacitors to 27pF on the TO220 drivers for stability because of the added band width of the outputs.
PNP complement - 2ST2121 if you are going complimentary.
It would be easier to email me for a schematic & board .JPG if you want.
I have also had meter's needles bent from full VCC outputs. An added diode and a couple of resistor changes on the meter PCB will stop that.
Good luck on the repairs.
Thanks BRUNNER2!
As a total newbie to all this, why are we concerned of Vbe? Aren't we just concerned about linearity of the input stage? It is easy to find darlingtons with hfe in the ten's of thousands, which ought to make the gain of the differential pair *very* linear, as the gain should be completely dominated by the resistors surrounding the pair.
Just to clarify, why worry about bandwidth when the input resistor in series with the capacitor is *strongly* limiting bandwidth? I believe the -3db point is 78Khz.
I'm quite inexperienced, but still pretty quick to pick stuff up -- even at my age...
eg. why not: www.fairchildsemi.com/ds/2N/2N7052.pdf ?
As a total newbie to all this, why are we concerned of Vbe? Aren't we just concerned about linearity of the input stage? It is easy to find darlingtons with hfe in the ten's of thousands, which ought to make the gain of the differential pair *very* linear, as the gain should be completely dominated by the resistors surrounding the pair.
Just to clarify, why worry about bandwidth when the input resistor in series with the capacitor is *strongly* limiting bandwidth? I believe the -3db point is 78Khz.
I'm quite inexperienced, but still pretty quick to pick stuff up -- even at my age...
eg. why not: www.fairchildsemi.com/ds/2N/2N7052.pdf ?
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Some data:
The left channel DC offset starts a -0.5 and continues to drop, past -10 volts before I shut it off...
Left channel Q6 base on turn-on is around -3 and continues to drop. Q5 voltages look fine, except for the connection to Q6.
Both Q1/Q2 collectors and Q3/Q4 emitters are at 10V, not 21 and 22.
Is it possible that a DC blocking cap isolating the Bias from the feedback loop has shorted? Perhaps a diode connecting the Q6 base to B+?
Thanks.
The left channel DC offset starts a -0.5 and continues to drop, past -10 volts before I shut it off...
Left channel Q6 base on turn-on is around -3 and continues to drop. Q5 voltages look fine, except for the connection to Q6.
Both Q1/Q2 collectors and Q3/Q4 emitters are at 10V, not 21 and 22.
Is it possible that a DC blocking cap isolating the Bias from the feedback loop has shorted? Perhaps a diode connecting the Q6 base to B+?
Thanks.
Hey there BigE
I have a broken 400 of my own. I drove 100 miles and the guy says durr it doen't work anymore and gave it to me although i donated 10 dollars for him to get a big bacon combo. Back home I fiddled the rca cables to almost falling off and dang it worked for a bit. I don't have an iron hot enough to replace the inputs so I decided to recap it without making an order to Mouser. I muffed up the board with some 470 caps instead of the 47 and upstairs it sits. I managed to fit some 22,000 caps in there before my recap attempt and was treated to a very nice sound improvement. Instead of looking at the voltage meters you can look through the gaping square holes at some big capacitors.
I have a broken 400 of my own. I drove 100 miles and the guy says durr it doen't work anymore and gave it to me although i donated 10 dollars for him to get a big bacon combo. Back home I fiddled the rca cables to almost falling off and dang it worked for a bit. I don't have an iron hot enough to replace the inputs so I decided to recap it without making an order to Mouser. I muffed up the board with some 470 caps instead of the 47 and upstairs it sits. I managed to fit some 22,000 caps in there before my recap attempt and was treated to a very nice sound improvement. Instead of looking at the voltage meters you can look through the gaping square holes at some big capacitors.
Well, it looks like it is fixed.
Left channel DC offset -20mv. Right channel +65mv. Bias will be around .4 V, both channels. Problems were broken traces, blown diodes and blown transistors on the PCB board. No doubt the blown stuff all occured due to not discharging the power supply when swapping out the caps.
I think I need to change the Right channel input differential pair to the same that was used in the left channel : MPSA06.
Currently, there is a TIS97 and an ECG product. When I measured the left channel, the hfe of the TIS97 was 575, ECG was 140. The MPSA06 I replaced were 310 and 330.
Has anyone tried MPSA06 for Q1/Q2? Results?
Left channel DC offset -20mv. Right channel +65mv. Bias will be around .4 V, both channels. Problems were broken traces, blown diodes and blown transistors on the PCB board. No doubt the blown stuff all occured due to not discharging the power supply when swapping out the caps.
I think I need to change the Right channel input differential pair to the same that was used in the left channel : MPSA06.
Currently, there is a TIS97 and an ECG product. When I measured the left channel, the hfe of the TIS97 was 575, ECG was 140. The MPSA06 I replaced were 310 and 330.
Has anyone tried MPSA06 for Q1/Q2? Results?
DONE!
I also replaced the ceramics. The 0.05 ceramics in the bias circuit were replaced by 0.047uf Vishay-roderstein MKP-1837 film caps, as were the 0.01 uF in the feedback loop.
Would using boutique caps make any difference in this circuit? (C4 and C18 from drawing 3 of http://www.hifiengine.com/manuals/phase-linear.shtml )
I also replaced the ceramics. The 0.05 ceramics in the bias circuit were replaced by 0.047uf Vishay-roderstein MKP-1837 film caps, as were the 0.01 uF in the feedback loop.
Would using boutique caps make any difference in this circuit? (C4 and C18 from drawing 3 of http://www.hifiengine.com/manuals/phase-linear.shtml )
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