bhjazz
Headphoneus Supremus
- Joined
- Dec 29, 2003
- Posts
- 1,534
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- 16
I took in an ailing Dynahi from member iamsmrt at the last Seattle meet. His initial symptom was that one of the RCA connections had come loose, and could I solder it back together. Well, at the meet, once the lid was off, we noticed something far more serious: all six PS caps were bulging out the top, and one had quietly loosened the plastic cap...
We powered it down and started looking around. The only other major feature we could spot is that the transformer was hot hot hot. Too hot to keep your hand on. In general, there are more problems here than just the RCAs...
Now that I have taken it in, I need some help diagnosing what went wrong. It is a Trevor Networks Dynahi. The PS caps are one of the few sets of parts that appear to be non-name. The caps are 63V/4700uF, and all have failed. The other major parts on the board are (from left to right with these parts at top):
2 LM338T
BB OPA541AP
MP930
BB OPA541AP
MP930
I do have a concern about the first OPA541 in that there is a nice smear of heatsink grease below it near the pins. I can only imagine this conducting some current, a little like flux does. Not the cleanest board build I've seen. I have not removed the PS board as yet to inspect the underside.
So here are a few questions for the Dynahi builders:
1) Is the PS circuit such that these PS caps are discharged? Or will they hold their charge for days on end? If they are discharged for sure, I'll pull the board and inspect.
2) What could have caused the bulging caps? It seems like something on that board, obviously, but are there any things I can look at that might be common? Would there be something on one of the other boards I could check for as well?
3) When I desolder the caps, is the heat from the iron going to put me at risk of those things blowing chunks?
Many thanks.
Now that I have taken it in, I need some help diagnosing what went wrong. It is a Trevor Networks Dynahi. The PS caps are one of the few sets of parts that appear to be non-name. The caps are 63V/4700uF, and all have failed. The other major parts on the board are (from left to right with these parts at top):
2 LM338T
BB OPA541AP
MP930
BB OPA541AP
MP930
I do have a concern about the first OPA541 in that there is a nice smear of heatsink grease below it near the pins. I can only imagine this conducting some current, a little like flux does. Not the cleanest board build I've seen. I have not removed the PS board as yet to inspect the underside.
So here are a few questions for the Dynahi builders:
1) Is the PS circuit such that these PS caps are discharged? Or will they hold their charge for days on end? If they are discharged for sure, I'll pull the board and inspect.
2) What could have caused the bulging caps? It seems like something on that board, obviously, but are there any things I can look at that might be common? Would there be something on one of the other boards I could check for as well?
3) When I desolder the caps, is the heat from the iron going to put me at risk of those things blowing chunks?
Many thanks.