Hi guys,
I'd like to say in advance, I'm not very savvy when it comes to electronics. My background is in software engineering, but I like solving problems(and saving money) and this is my dads old amp, so I'd really like to see if I try and fix it.
The problem:
I have a Yamaha RX-V340 RDS, that is going into protection mode on startup. In the diag menu, the error log reads: 'DC PRT 14%' (The percentage amount sometimes fluctuates between 9 and 16%), which according to the service manual means "The DC output of the power amplifier is abnormal".
My deductions so far:
When putting the amp into protection override, I'm measuring DC volts on the output terminals of -1.4V on the RR, R, L and RL channels. Basically everything except center.
Initially I was told it could be a DC offset adjustment issue, but after looking there are no potentiometers on this board, so I'm not able to adjust that.
My board has 3 big 'IC's. One for center, and one each for R and L, which contain the outputs for both main and rear within them. From the service manual(schematic on page 56) I can see that the outputs for the rear and main channels of a single IC should all read roughly zero, however I'm getting -1.1V on all. That must be related to my +- -1.4V on the outputs, no?
It's also worth noting that I'm not getting the expected (roughly) -40V on pins 5 and 12 on either IC302(R) or IC303(L), and also not on pin 5 of IC301(C). Instead I get around -1V on those. I'm not sure how this could be related, but it does seem pretty far off from where it should be.
This all makes me think there is some issue upstream from the each channels power amp, since they all have similar problems. But then again, I am not too clued up here.
Am I on the right track? Any ideas for things to try which might narrow it down?
Service manual: Download Yamaha RX-V340 Service Manual | ManualsLib
Thanks for your time!
Rob
I'd like to say in advance, I'm not very savvy when it comes to electronics. My background is in software engineering, but I like solving problems(and saving money) and this is my dads old amp, so I'd really like to see if I try and fix it.
The problem:
I have a Yamaha RX-V340 RDS, that is going into protection mode on startup. In the diag menu, the error log reads: 'DC PRT 14%' (The percentage amount sometimes fluctuates between 9 and 16%), which according to the service manual means "The DC output of the power amplifier is abnormal".
My deductions so far:
When putting the amp into protection override, I'm measuring DC volts on the output terminals of -1.4V on the RR, R, L and RL channels. Basically everything except center.
Initially I was told it could be a DC offset adjustment issue, but after looking there are no potentiometers on this board, so I'm not able to adjust that.
My board has 3 big 'IC's. One for center, and one each for R and L, which contain the outputs for both main and rear within them. From the service manual(schematic on page 56) I can see that the outputs for the rear and main channels of a single IC should all read roughly zero, however I'm getting -1.1V on all. That must be related to my +- -1.4V on the outputs, no?
It's also worth noting that I'm not getting the expected (roughly) -40V on pins 5 and 12 on either IC302(R) or IC303(L), and also not on pin 5 of IC301(C). Instead I get around -1V on those. I'm not sure how this could be related, but it does seem pretty far off from where it should be.
This all makes me think there is some issue upstream from the each channels power amp, since they all have similar problems. But then again, I am not too clued up here.
Am I on the right track? Any ideas for things to try which might narrow it down?
Service manual: Download Yamaha RX-V340 Service Manual | ManualsLib
Thanks for your time!
Rob
Is there +40Vdc (approx) on IC pins 4 and 8?
Probably both +ve and -ve rails are "disconnected" because amp is in protect.
If +ve rail is up then troubleshoot missing -ve rail.
Probably both +ve and -ve rails are "disconnected" because amp is in protect.
If +ve rail is up then troubleshoot missing -ve rail.
Hi, thanks for your reply. Yes, the +40Vdc is present on 4 and 8, on both the L and R ICs. I also had a suspicion that is was because of the fact that it's in protect mode.
Oh I see what you are saying. If the two +40Vdc (+ve) pins are correct, but the two -40Vdc pins are not, the issue is then with the -ve rail (the sources of the 2 -40Vdc pins).
Appears that +ve and -ve rail is from the unregulated supply, ie, diode bridge D327 and main caps C349, C350. Diode check D327 and consider testing/replacing C350.
Okay great, I have tested the outputs of D327 and I get -44Vdc and +44Vdc on either output. Will pull and test C350 now.