So according to the manual, that diode is a RD3.9EB2 and I am looking at the datasheet to try to find a suitable replacement and once I start filtering in digikey or mouser, etc some of the other specs don't align perfectly and I am not sure which things can be used. I assume I want the max 50 ohm impedance so anything over that is no go, like the third item:
The 1N5228B will do fine. There is tolerance in the specifications anyway, so order a few and match a pair. Basically the lower the dynamic impedance is, the better the zener diode is (better voltage regulation with current changes).
You don't have to match them freaky close, and there will be Vbe differences in the two transistors on top of that. Going from one diode type to another would be greater, and you want them to track with varying current (dynamic impedance). Would it work if you didn't? Yes, but it should work better and as intended doing it the right way. They didn't take time to match the parts in the factory either in case you're wondering, but they wouldn't mix device brands either.
You don't have to match them freaky close, and there will be Vbe differences in the two transistors on top of that. Going from one diode type to another would be greater, and you want them to track with varying current (dynamic impedance). Would it work if you didn't? Yes, but it should work better and as intended doing it the right way. They didn't take time to match the parts in the factory either in case you're wondering, but they wouldn't mix device brands either.
So I sent the wrong info it was actually D609 that shorted so I will also be replacing D608 I suppose. Unfortunately because of my mix-up, I ordered the replacement diodes for D601/602 and these are 1SS81 diodes which again I am not sure what to replace with. 🤦♂️When I read the datasheet, I am unsure which aspects are mandatory and which ar minimums that can be exceeded etc. My best guess is I can use 1N485B as a replacement for those. How did I do?
If you looked it up, you'll find it is just a 200 mA signal diode. It has a peak reverse breakdown rating of 200V. Look one up on Digikey or Mouser and use that.
You only need to replace the one that shorted.
You only need to replace the one that shorted.
I kinda psyched myself out. After replacing the diode, I was getting different voltages at points on the board I expected to be the same between L and R channels. I went down another rabbit hole removing components looking for another bad diode or shorted transistor or cap and didn't find anything. I ultimately decided to put everything back, re-connect the driver transistors on the heat sink and everything worked. I guess I still have a lot to learn but to be fair, these circuits seem complicated even for someone with more experience than me.
Once again this is an invaluable resource and my friend's amp which had been sitting in its box for several years can be heard again. I really appreciate everyone's help and can't thank you enough.
Once again this is an invaluable resource and my friend's amp which had been sitting in its box for several years can be heard again. I really appreciate everyone's help and can't thank you enough.