GC1038 - Issues Halp!

[Ben78]

Hi All!

This is now getting beyond my skill.... I have a GC1038 that I was probing to find the frequency and I slipped when I touched the board and the good old 'pop' happened. I smelled smoke but didn't see where it came from unfortunately.

Now the detector still works! But if the disc is below 2/3 detection will set off an osciallation in the audio that remains until I turn the disc back up, additionally the pinpoint function doesn't seem to work, depth is reduced and when waving the coil over a discriminated item it will give a stuttering audio...



Sorry for such a large file, it is full resolution from my SLR.

Now, I was probing the through-hole near the adjustment pot and I slipped onto a leg of the pot. The pot appears to set the '0' point for the pinpoint control. I replaced the TL064C closest to the pot and pinpoint button, due to the oscillation I thought maybe I had toasted one of the opamps in there. This made no change to the symptoms.

Without resorting to replacing every IC on the board, has anyone got any suggestions on where to go next?

Thanks

Ben

[chemelec]

I Saved the Picture to my computer and Zoomed Full Size.
VERY BIG, NICE CLEAR PICTURE.

But I can't see any suspicous Burn.
What about the Other Side with just Traces?

Also with Power on, Possibly check Voltages on B, C and E of the transistors.
Not Exact measurenents, but to see if they appear Reasonable.
(Example: TYPICALLY "E to B should be about 0.6" and "E to C should be Higher".)

[Ben78]

Thanks, I'll start checking the trans - I just figured with an oscillation it was a breakdown in a Op Amp somewhere... I have been over the whole board front and back with a very high quality loupe and cannot see a single 'ah-ha' fault!

[migusch]

Q2 and R5 seem to be suspicious to me.
The board is "dirty" with solder residues in some places and a wax-like substance next to the switch. I would carefully clean it with isopropylic alcohol and a toothbrush. After that, one could see more in those areas.
There is a piece of solder-tin below the switch on the photo. Quite dangerous - this can shurtcut something when it comes loose.
Very nice photo - it is not easy to take that clear photos of circuit boards without reflections.

[Koala]

Fairly sure there is some damage in the center of Q12 top right corner. Could be a trick of the light or a blob of solder though

[sido]

Hi All!

Now, I was probing the through-hole near the adjustment pot and I slipped onto a leg of the pot. The pot appears to set the '0' point for the pinpoint control. I replaced the TL064C closest to the pot and pinpoint button

Thanks

Ben

Hi Ben, are you talking about the trim pot labelled 104. Check pic below, Also look at U1 IC...



Cheer's Sid