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.
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.
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...
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...
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?
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?
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.
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.
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).
Rich J
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).
Rich J
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.
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.
You really need an oscope and signal generator to troubleshoot this fault.
The feedback coupling cap djk referred to is C8 in the DH220 manual. It's one of three electrolytics on each driver board. Replace all of them. Check R25 through R28 for the proper value.
Have you checked the output fuses? If they are blown a small distorted signal will make it to the output through R34//C18.
The feedback coupling cap djk referred to is C8 in the DH220 manual. It's one of three electrolytics on each driver board. Replace all of them. Check R25 through R28 for the proper value.
Have you checked the output fuses? If they are blown a small distorted signal will make it to the output through R34//C18.
Thanks for all responses. I checked C8 (470mfd), its good. Check the other 2 electrolytic caps, i.e. C12, C14 (100mfd) and they are good. Check the two resistors near C8, R25 and R28 and they're good.
No add-on input gain is installed only the factory output gain pots on rear of P230 amp.
I checked transistors Q1 to Q13 and I've determined the left channel Q3, Q4 and Q6 are bad compared to the right channel. Forgot to check the mosfets voltage before I put the lid on. I set the bias down to 275mA.
OK, I see there is a repair kit sold on Ebay for the 220, P230 amp, I'm wondering if its worth $26 bucks? Should I borrow an O-scope from work for more investigation? Why is it both channels and not just the left channel?
No add-on input gain is installed only the factory output gain pots on rear of P230 amp.
I checked transistors Q1 to Q13 and I've determined the left channel Q3, Q4 and Q6 are bad compared to the right channel. Forgot to check the mosfets voltage before I put the lid on. I set the bias down to 275mA.
OK, I see there is a repair kit sold on Ebay for the 220, P230 amp, I'm wondering if its worth $26 bucks? Should I borrow an O-scope from work for more investigation? Why is it both channels and not just the left channel?
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I compared left channel board, E B C voltages, to measurements from right board and also a second amplifier.
Q3 B ~-2mV, Q4 E ~ -1.5mV, Q6 E ~ 6.19mV. Per the manual, respectively
Q3 B 220mV, Q4 E 320mV, Q6 E 800mV. Now I'm not 100% sure these are bad but from the measurements, there is an issue.
I'll borrow an O-scope soon.
Q3 B ~-2mV, Q4 E ~ -1.5mV, Q6 E ~ 6.19mV. Per the manual, respectively
Q3 B 220mV, Q4 E 320mV, Q6 E 800mV. Now I'm not 100% sure these are bad but from the measurements, there is an issue.
I'll borrow an O-scope soon.
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