Is an overheating IC a dead IC? Boss DF-2 repair

[clarisso11]

Hi everyone!

I've been working on a Japanese made Boss DF-2 lately, and was hoping to get some insight from someone more experienced in electronics than I am.

My basic question is: If an IC in the effects circuit is overheating (almost too hot to touch), is it most likely that the IC has gone bust (shorted out)?

More specifically, it's an HD41001BP IC, and the pedal is operated with a fresh 9V battery. All 9V points in the circuit measure too low, at around 5V, and there is some voltage at ground (although only around 10mV). Capacitor C36 was loose at one end, and has been soldered back. The battery was still connected when it was loose, maybe that could have caused a short? The LED is flickering and dim (I'm assuming due to the voltage drop), and the footswitch has no effect. Electrolytic capacitors have been checked with ESR meter, and all cables are properly connected.

My first impulse would be to replace the IC, but I'm not sure this makes sense..

Here's the service manual: https://www.synthxl.com/wp-content/u...rvice-note.pdf


Any advice or nudge in the right direction is appreciated!

[Mick Bailey]

It could be that the IC is shorted internally. I would desolder the affected part and establish that the 9v is restored with it removed. If that's the case then do a resistance check between the 9v+ and each vacated solder pad with the battery removed. The only low resistance reading should be the 9v supply to the IC on pin 14. If the resistance readings are good the chances are that the IC is at fault. If you get any low resistance readings on any of the other pins then it would need further investigation.

[clarisso11]

It could be that the IC is shorted internally. I would desolder the affected part and establish that the 9v is restored with it removed. If that's the case then do a resistance check between the 9v+ and each vacated solder pad with the battery removed. The only low resistance reading should be the 9v supply to the IC on pin 14. If the resistance readings are good the chances are that the IC is at fault. If you get any low resistance readings on any of the other pins then it would need further investigation.

Hey Mick,

thanks for the reply, that's exactly what I was looking for! I unsoldered the IC, and 9V was restored. Only resistance from 9V+ to pin 14 is low, so the IC might indeed be bad. I ordered a replacement, and will update once it arrives.

This is a really neat trick for checking ICs! What is the theory behind it? I'd love to learn

[clarisso11]

Update: The chip arrived today, and the pedal is now working again - so in this case, the heat coming off the IC gave the problem away. Thanks again to Mick Bailey !