SX980: dead stv4h diodes?

I'm working my way through the repair of an SX980. With the help of Markthefixer, I corrected the power supply voltages. I also recapped the protection and amp boards. The next step was to reconnect everything. When I got the diode stv4h, I thought it would be a good idea to test it before soldering it into the board. Actually, I was thinking of this step as kind of a formality, but then my meter returned "OL" in both directions, for both diodes. Reading the threads on STV-4H here, I got the impression it was a pretty hardy part -- I didn't find any posts where both diodes were simultaneously dead. Hmm. I unscrewed each diode and removed the insulation from the leads. The leads look unbroken but are pretty badly blackened -- I wonder if this is normal. I scraped them with a razor blade to get a good surface for the meter to contact. Still OL, both ways. Thinking my meter might be bad, I used it to test a new zener diode -- that one gave me the expected voltage. the low battery indicator is not on.

I guess my main question for the gurus on this forum is: what should I do next? I still wonder whether my tests are valid, and if they are, what could have caused both of these parts to fail. Relatively recently, this was a working amp. Sadly, the original part seems to be unobtainable. I read some discussion about substitution, but didn't find anything definitive. Someone also mentioned buying lesser, broken "parts" amps on ebay and extracting the part. I would go to that length, if necessary, but would like to avoid it.

I'm at a standstill here. Any help or advice would be greatly appreciated.

sometimes a meter doesn't have enough voltage to push a stv-4h into conduction. A 9v battery and a 1200 to 1500 ohm resistor will do it, and then read the volts across the diode. One way will be 9v the other way will be 2.1 to 2.3 volt and sometimes the highest a meter mayl go in diode mode is 1.999 volt....

The forward voltage also varies with the amount of forward current, Pioneer (and their specification) runs them at 7 milliamps of current, and that resistor will get you into the ballpark without going over. The meters run a current quite a bit lower than that and just at the moment I think (but don't COUNT on it, I'll have to check this experimentally and edit if I was wrong (or right)) that lower current = higher voltage drop.

Mark, thanks for your quick reply. I was really hoping there was some way the test could be bad while the meter is good. I think have some 1500 ohm resistors around. I'll try it when I get home and let you know the result.

Thanks!

If the diode was open (or installed backwards), the result on power-up would not be to your liking. Once you confirm that the diode is OK, make sure you install it properly.

That is an understatement!!! A doozy!!

Smoking ruin comes to mind....

Thanks EchoWars and Mark for the advice. Smoking ruin is definitely something I want to avoid!

The test went very smoothly, mostly because I had the necessary items on hand (battery, connector, 1k5 resistor, breadboard). The results were 2.134 and 2.125 volts. My tests show the side with the little green dot is the cathode. I think this means the diodes are both good, which is great news. I'll put their "leg warmers" back on and solder them in. After that I'll make the rest of the connections, double check them, and power on with DBT. My progress is unblocked! Thanks for your help.