Possibly a dumb question, what can cause a zener to fail?
The particular diode in question is reading 2 ohms in both directions and is part of the output drive voltage regulation (possibly not the correct term) of an Alpine MRV-M500.
It took me ages to figure out why I only had a drive signal on the high side output and not the low side. There were a few other bad parts in the output drive section as well but they were fairly easy to identify.
The particular diode in question is reading 2 ohms in both directions and is part of the output drive voltage regulation (possibly not the correct term) of an Alpine MRV-M500.
It took me ages to figure out why I only had a drive signal on the high side output and not the low side. There were a few other bad parts in the output drive section as well but they were fairly easy to identify.
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These amps aren't generally worth repairing because the driver ICs are too expensive. The ones from chinese suppliers have a hit and miss reputation.
If nothing else failed around the zener circuit, I'd guess that it's a random failure.
If nothing else failed around the zener circuit, I'd guess that it's a random failure.
Yes, I'm familiar with their obnoxious custom IC. $25-$30 for one chip is absurd and I condemn the decision to not use an off-the-shelf part.
Nothing else in the regulation circuit failed, only the zener. So I guess random failure then?
Thanks, Perry. I like to understand the "why" when possible.
Nothing else in the regulation circuit failed, only the zener. So I guess random failure then?
Thanks, Perry. I like to understand the "why" when possible.
http://cdn14.21dianyuan.com/download.php?id=170219
This is a PDF "failure Modes of Electronics"
Page 15 for a general beginner's description of a Zener failure. Page 64-65 for Zener diode theory.
This is a PDF "failure Modes of Electronics"
Page 15 for a general beginner's description of a Zener failure. Page 64-65 for Zener diode theory.
If you want to get a better idea of what possibly caused it, use the supply voltage feeding the voltage dropping resistors and calculate the power dissipation in the Zener. If it was being run at its limits for power dissipation, that might explain the failure. I don't remember ever seeing anything about this diode failing in other MRV-M500 repairs.
If the zener reads zero but the pass transistor is OK, you should see about a volt output instead of 12V. If that is not the case chances are that the pass transistor is shorted and took the zener with it.
Another cause could be that the resistors feeding the zener burned out (lower resistance) and overloaded the zener.
So I think you should do a bit more diagnostics. IF the transistor and surrounding resistors are OK, replacing the zener might fix it - it might just have failed as they sometimes do for no apparent reason.
Jan
Another cause could be that the resistors feeding the zener burned out (lower resistance) and overloaded the zener.
So I think you should do a bit more diagnostics. IF the transistor and surrounding resistors are OK, replacing the zener might fix it - it might just have failed as they sometimes do for no apparent reason.
Jan
twilliar-
Thank you for sharing that. The sections you listed were interesting enough I'll be reading the whole thing as time permit.
Perry-
That's a good suggestion, perhaps one of the resistors is out of spec. I'll give them a close inspection and calculate the dissipation.
Jan-
I didn't write down what the voltage was but it was quite low, ballpark of one volt sounds about right.
I checked the other components and nothing was obviously wrong so I swapped in a good zener to test and now have both drive signals at the outputs.
Thank you everyone for the helpful contributions!
Thank you for sharing that. The sections you listed were interesting enough I'll be reading the whole thing as time permit.
Perry-
That's a good suggestion, perhaps one of the resistors is out of spec. I'll give them a close inspection and calculate the dissipation.
Jan-
I didn't write down what the voltage was but it was quite low, ballpark of one volt sounds about right.
I checked the other components and nothing was obviously wrong so I swapped in a good zener to test and now have both drive signals at the outputs.
Thank you everyone for the helpful contributions!