Yamaha R-1330 amplifier repair

[DarthLowen]

Hi guys,

I'm having some issues troubleshooting my brother in law's Yamaha R-1330 amp and since I'm relatively new when it comes to analog electronics debugging, I thought I'd give my favourite electronics youtube channel forum a try.

My brother in law was listening to some music when all of a sudden the amp just stopped and the power LED started blinking. Apparently, this is some sort of protection mode. Accessing the diagnose menu was easy enough (service manual: https://elektrotanya.com/yamaha_mcs-1330_r1330_ns-bp400_sm.pdf/download.html) The first and only thing it says was 'DAMP' (at first I thought, water damage?) after which it turned off again immediately. According to the manual, this means that there's an issue with the Digital AMP circuit. Sure enough, when I started measuring some basic voltages, the circuitry that creates the +/-5D and +/-5A (schematic MAIN 4/4, E2/E3) created +6V and -4V, which seems off. I replaced the Zener diodes (D516 and D517) and the transistors (Q503 and Q504) and now I have +/-4.8V, which is probably more or less ok.

After this change, the amp still powers off, this time I get the error 'PSD: 124' Which is again related to the digital amp I guess. Here the confusion starts, both DAMP and PSD: x point to the same chapter in the service manual (p.30 AD DATA CHECK), so what's the difference with the previous error? I checked the PS_DAMP voltage and that's exactly 1.9V as the schematic suggests (MAIN 1/4, pin 95 of the processor), also, when I force the '/ERROUT' signal from the modulator to the CPU (MAIN 4/4, mod IC pin 19) to 5V (I know I know, don't do this :-P) I can access the diagnose menu and the DAMP reading is correct at 94 (PS1 as well at 124)?

I did notice that the '/ERRIN' signal (MAIN 4/4, mod IC pin 20) triggers, so when I started to trace that problem, I traced it to diode D538 (MAIN 4/4 I8), the input to that diode is not 0V as suggested, but is 4.8V. This is, I believe, the reason the ERRIN signal triggers. However I can't wrap my head around the circuitry behind this diode. I noticed that as soon as the gate of Q520 (MAIN 4/4 K8) goes to -5.8V (unmute?), the drain pin goes to -0.59V instead of the 0.2 it should be. I just have absolutely no idea why because I just don't understand the circuit.

Some basic measurements I did (MAIN 2/4):
+/-B: +47.49V and -47.05V, (should be closer to 44V according to the schematic, but considering that they probably have 220V in Japan and I'm closer to 240V AND that this voltage is not regulated (straight from the transformer into a full-bridge rectifier and some big a$$ caps) this seems OK to me?
+/-12A: +/-11.7V, close enough, right?

/edit: thought I'd share the part of the schematic I don't understand:


All and any help is more than appreciated. Learning as I go...

Thanks!

Nic.

[DarthLowen]

So I've done some more digging around. I decided to replicate the circuit in LTSpice and feed it my voltages and see what comes up. Apparently I missed 1 crucial detail, this circuit is connected to the output of the driver circuit and my -0.59V comes from there. I checked by removing resistor 633 and sure enough, the /ERRIN signal goes high (as in, to +5V).

The problem is thus somewhere in the driver circuit, which sounds typical judging from several other amp-repair posts across the internet. So, I guess I'm on the right track, right?

I measured the voltages at the driver IC:
- pin3 (input signal) is -4.8V instead of -2.4V, but this could be due to a feedback loop back into the modulator? It's trying to compensate for the wrong output?
Votlages on pins 13, 14, 15 and 16 are WAY off:
- pin13: -46.6V iso 0V
- pin14: -46.6V iso +6.2V
- pin15: -32.3V iso +14.5V
- pin16: -42V iso 7.3V

I'm just not sure which component is broken now, the driver IC or the MOSFETs (Q512/Q513)? It's impossible to measure the IC (wouldn't know where to start) and the mosfets are SMD components, which are also impossible to measure while mounted.

Should I just replace both and try my luck?