813B power transistor in SMD.

[Bernardo]

Hi everyone. it turns out that my alesis dm pro unit has background noise, I thought of recapping the electrolytics since it is an old unit and I thought it was the fault. when i open the unit i find a small transistor-regulator? which exploded I can't find a spare part for this component, it must be discontinued. Could you advise me a more modern compatible substitute of 813B?Thanks a lot.

 

[Khron]

What sort of symptoms does your unit show? And was it working at the time when the part seemingly exploded?

 

[Bernardo]

Te machine works fine,only a bit of noise.

 

[Khron]

Would there be a chance that the (presumably analog) noise is perhaps NOT coming from the MIDI in/out are? And what sort of noise is it? And has that started only recently, or..?

That yellowed / browned area looks more like flux than a burn mark.

 

[user 130681]

The 6N138 is a darlington opto coupler. Unlikely to have failed.
https://uk.rs-online.com/web/p/optocouplers/5473706

 

[Khron]

I'm reasonably sure the OP meant the SOT-23-packaged part, much closer to the 74VHCU04 chip. That one is indeed marked "813B" (similar but not identical to "138").

 

[user 130681]

Ah, I see now.
Looks like a voltage supervisor chip. I can only find a TO92 version and I doubt it is faulty as that gunge on it looks like old flux.
If it needs replacing, they are available in pack of 5. Maxim Integrated Voltage Supervisor 3-Pin TO-92, DS1813-10+ | RS Components

 

[Khron]

Regardless, highly unlikely such a part is to blame for (seemingly) analog audio noise.

 

[JohnRoberts]

It looks like they are out of production, but still thru hole parts around.

JR

 

[Bernardo]

the blue electrolytic that is near the 813B also looks defective, it has traces of an explosion, it may have burst and released flow on the 813B
TO-92 Pin, DS1813-10+ | RS components that Jon S advises is the right one?
I'm going to recap the electrolytics, I will change the 813B and some regulator, the unit gets very hot.
very grateful for all the help.

 

[user 130681]

The regulators will get very hot because they have no heat sinks as they are designed to work comfortably at 85°C. If the regulated voltages are correct, leave them alone.