Troubleshooting Hafler P230. - diyAudio
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Old 22nd July 2007, 09:08 PM   #1
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Question Troubleshooting Hafler P230.

I recently recapped my P230 (same as DH220, just another pair of output transistors, driver board is exactly the same PC-19C)

Pin 4 was shorted to ground accidentily, and the positive rail fuse blew a couple seconds after turning the amp on. So the left channel was powered with just the negative rail for about 3 seconds.

After finding the short and replacing the fuses the left channel has 400mV of dc offset.

I started checking transistors. PS measures +/- 62v. I got to Q8 and found that its collector measured negative .4v instead of the positive 1.5v it is supposed to be. Q8's emitter and base connections were the correct voltage. I also checked the output mosfets which have the correct voltages at their connections.

My basic understanding would say that Q8 has failed, but i wanted to ask your guy's opinion. If no one has any further suggestions i will continue checking volatges, and replace Q8/11 and Q12/13 with matched parts for hfe and see where that gets me.

Thanks for any help you can offer.
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Old 22nd July 2007, 09:37 PM   #2
Nordic is offline Nordic  South Africa
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If you can remove the transistor....

Put your multimeter in diode test mode... connect one probe to base... touch the other 2 legs individualy, they should both read 1 or they will both measure a resistance probably somewhere between 600 and 900ohm....

Connect the other probed to the base.. do the same test... results should be inverse of first test...

finaly test collector to emitter swapping polarity, to make sure it does not conduct either way around...
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Old 23rd July 2007, 02:01 AM   #3
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Shorted pin 4?

Q12 and Q8 probably gone, I would also replace C8 again.
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Old 23rd July 2007, 02:35 AM   #4
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Thanks for the help DJK, i will order parts tomorrow. Yes i shorted pin 4 to ground. I know, amazing stupidity at work, but hopefully i can get the amp going again.

Next question. Wouldn't it be better to move the pwr. supply bypass caps (C21, C22) to directly across the cap terminals instead of on the pcb? Or is it better for the bypass caps to be closer to the circuit?
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Old 3rd September 2007, 04:00 AM   #5
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Wow, its been a long summer and i haven't had much time to work on this amp. Finally i have it working though. I replaced all four driver transistors (at least one, Q12, was cooked, i didn't bother testing the others).

I also had to replace the biasing transistor, Q9, and two diodes D11/D12. I also replaced the 470uf BP capacitor.

DC offset is low around 20mv, and holding steady. Bias current is set at 270ma on both channels.

Thanks for the help.
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Old 13th March 2014, 06:56 AM   #6
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Bought this P230 from Ebay, its output level is low. I compared output level of another 230 using 100Hz tone, 2V output, the bad P230 measuremed only 1V (either channel). Opened the amp, looked inside nothing obvious. Any ideas what could cause low output level in both channels?

I adjusted bias level, to 375mA (<-the good P230 is that value). Still low output level (as I read in other thread makes no difference in output setting).

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Old 14th March 2014, 01:26 AM   #7
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If the cap in the feedback loop goes open, the gain of the amplifier drops to unity (1).

Small electrolytics caps in the signal path are always a problem.
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Old 14th March 2014, 03:24 AM   #8
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DJK, thanks for the tip. Can you provide more detail on which cap to check in the feedback loop. Where or what part do I look first? I have the dh220 manual, I see I can check voltages of board transistors etc. (I will borrow a DMM 199,999 count from my work this weekend).

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Old 14th March 2014, 05:57 AM   #9
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If you can't find the only electrolytic in the feedback loop, you really shouldn't be inside an amplifier.
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Old 14th March 2014, 08:33 AM   #10
Mooly is offline Mooly  United Kingdom
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If both channels are the same then it sounds as if its going to be "normal"... as in not faulty.

Only two things ordinarily determine the gain. First is the feedback factor determined by the ratio of the network components (but if both channels are the same then its hard to see both having a problem). Secondly, has an input attenuator been fitted (either as a mod or as a factory option).

Edit... the input sensitivity is quoted as 1.55vrms for 115 watts into 8 ohms. That translates as a voltage gain of fractionally under 20.
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