Aguilar db750 intermittent power down

[PocketProtector]

Anyone ever have trouble with a Aguilar db750 going into protection mode intermittently?
I bought this amp used at GC a few years ago and it’s consistently done this (inconsistently). I brought it to a local tech who said he saw it fail once but couldn’t get it to do it again. When I brought it home it was failing every 5 or 10 minutes. I had already replaced tubes. I monitored B+dc seemed fine, no dc on speaker output temp switches on heat sink not activated. I ordered all the ic chips on the power monitor board (top board) they’re all socketed so they weee easy to swap.
That fixed it for about a year but now it’s doing it again!

 

[Old Garage-Bander]

Find a tech that knows what he’s doing. (Not talking about you, but the other guy.)
If he just sat their and waited for it to fail, then he only did half a job with the diagnosis.

This amp seems to have a flaw somewhere that is causing the problem.
There are troubleshooting methods that one can use to expose those flaws.

Did the tech you took it to use your cab for testing?
Did he use a variac to simulate different line voltages?
There are still other things that can be done.

Intermittent problems are a tech’s nightmare.
Some just don’t want to bother going to the trouble of working on them because they can take up a lot of time.

Have you considered a consultation with Aguilar?
Either to see if they can point you in the right direction, diagnostically.
Or in regards to sending it to them, or a recommended Aguilar tech for repairs.

 

[PocketProtector]

I did speak with Aguilar back before I brought it to the local guy they seemed helpful I might try them again. Really I’d just like to avoid the shipping cost back to them. The amp is so heavy and with it being intermittent I’d hate to pay to ship it and still not have it fixed.
I think the variac idea is a good one maybe the line voltage is low at my house when it happens. I can actually borrow one from work to test that. Thanks for the input.

 

[PocketProtector]

Btw it has happened with both of my cabs so it’s not a short in the cab

 

[Old Garage-Bander]

I did speak with Aguilar back before I brought it to the local guy they seemed helpful I might try them again. Really I’d just like to avoid the shipping cost back to them. The amp is so heavy and with it being intermittent I’d hate to pay to ship it and still not have it fixed.
I think the variac idea is a good one maybe the line voltage is low at my house when it happens. I can actually borrow one from work to test that. Thanks for the input.

Or higher voltage than at the tech’s bench.

Proceed slowly with the variac. Give plenty of time for the issue to develop before moving on to a different setting.

If the variac presents some correlation between frequency of the problem and line voltage, are you fully prepared to jump in and fix it yourself! If not, maybe someone else needs to be looking at it. Does the variac have voltage and current meters on it? Or do you have external meters you can use with it?

It may cost a pretty penny to ship it somewhere, but how does that stack up against the cost of randomly replacing parts just because they are easy to replace?

Perhaps Aguilar can direct you to someone within a reasonable driving distance?

Good luck.

 

[PocketProtector]

Just an update on this. I noticed one of the caps on the power supply controller board looked slightly puffed out on top. So I ordered a replacement from mouser.com (also replaced the one next to it looked like they were a pair)
And so far so goo, seems to have fixed it.