Phase Linear D-500 DC Protect (and other questions)

Another suspect component:

Photos from amp1 and amp2 - same damage to both.

IMG0312183029.jpg
IMG0312183046.jpg
 
All op-amps are suspect in that amp, if you do anything get some good sockets and solder themm in place so swapping op-ampps is easy. There are some more modern choices for the 4558.
 
The 4558s do seem to have failed on both amps. When I pulled them, the 15v rails stabilized (previously all over the place and causing the 3k 5w resistors to run scalding hot) and Hi-Freq lights went off.

I went ahead and took an inventory of all caps and opamps, and ordered new+extras from Mouser. I also ordered some new resistors to replace some select ones that look to have run hot for a while. When the order comes in I'm going to recap everything and replace the opamps. I am going to go the socket route and ordered 4558s for testing as well as OPA2134 to use in the final product once I'm confident they won't be quickly destroyed.

I'm looking at PS cap replacement but haven't made a decision yet. Each amp currently uses 2x 125v 13000uf caps and I'm looking at 160v, 20000uf+ replacements, but they're expensive.

All the LEDs work great!

I'm still trying to figure out why one amp is permanently on. The power switch itself hasn't failed, but I can't find the issue. Hoping I'll run across it when recapping anything. Any thoughts? The impedance switch on the other amp doesn't work, but I haven't even taken a look at it.

None of the fuses for the output transistors blow, so that seems like a good sign.
 
One of those 3 big relays controls the input power. The other 2 are DC protect and hi/low rain voltage. That amp senses what kind of load it's hooked to and if the load is too low in ohms it will switch in the lower rail voltage to save itself.Hiz/lowZ switch accomplishes this..
 
Have you checked the size of the new PS caps, those new ones are probably much taller..
 
laatsch55 said:
Have you checked the size of the new PS caps, those new ones are probably much taller..
Click to expand...

That's been my search criteria on mouser. I can find some with close to the same capacity as these, but they're almost half as tall...
 
FWIW, it may not be the op-amps that are faulty but what they control, when bringing the amp back up, use your variac and I've found if the variac is used in series with a DBT your chances of not hurting parts is much better. A variac will limit voltage but not current and current is usually what kills an amp...
 
jshupe said:
That's been my search criteria on mouser. I can find some with close to the same capacity as these, but they're almost half as tall...
Click to expand...

Well that's not near as bad as TOO tall....
 
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