Drawmer DL441 - Noise on All Channels?

[outoftune]

I have a Drawmer DL441 in for service. The unit is outputting white noise and some oscillation / motorboating from the outputs on all 4 channels.

I suspected something in the PSU, but I've replaced the main 2200uf PSU caps and rectifier diodes with no change to the noise. I'm able to measure +/- 15VDC output from the regulators.

Does anyone have an idea of what else could be causing this? I've searched around online and have seen some people who have had issues with the power transformer of the DL241, wondering if that's suspect in this unit?

I see a few of the 220uf output coupling caps look a little buldged, I may try replacing those but I'm not sure that's the root of the issue here.

Any Drawmer experts out there have any ideas?

 

[mrclunk]

We have a bunch of these.
Power transformers defo can be an issue, get really hot and die.
Also had one where most the 4.7uf electo caps were failing and some leaking / eating through traces on pcb. Assumed that was a bad batch of caps. Look for slime around the cap bases.

Any components significantly hotter than others, something might be shorted out?

 

[outoftune]

We have a bunch of these.
Power transformers defo can be an issue, get really hot and die.
Also had one where most the 4.7uf electo caps were failing and some leaking / eating through traces on pcb. Assumed that was a bad batch of caps. Look for slime around the cap bases.

Any components significantly hotter than others, something might be shorted out?

Hey thanks for the info. I'll take a look at the 4.7uf's and check if other components are getting hot and report back.

With the PSU Transformer, do they typically just fail dead after overheating or it's more gradual?

 

[JohnRoberts]

DO you have an oscilloscope? If yes look at the PS rails to confirm they are clean.

JR

 

[mrclunk]

Hey thanks for the info. I'll take a look at the 4.7uf's and check if other components are getting hot and report back.

With the PSU Transformer, do they typically just fail dead after overheating or it's more gradual?

gradual heat death with the transformers. They can start audibly vibrating, really hot to the touch.

 

[outoftune]

DO you have an oscilloscope? If yes look at the PS rails to confirm they are clean.

JR

I do have a scope, I'll give that a look as well, thanks for the tip!