Triple Chorus EQ section dead.

[LektroiD]

I managed to get my hands on a NoS Triple Chorus from Random Source stock. Built, but with a dead EQ section:

1) EQ section is completely dead (no sound whatsoever when EQ mode selected). I used a rotary switch and verified connections many times.

2) Both chorus settings work, but sound exactly the same (linear & solina). Possibly due to a faulty EQ?

3) Opamp under the Mid EQ level socket is ridiculously hot. It is not possible to leave your finger on for more than 1 second (unless wearing asbestos gloves).

I have tested voltages going to these, but appears to be negative voltages (-V), rather than +V.

I have swapped out the hot chip and replaced, the new one also gets extremely hot very fast (you can't touch it for long with your finger).

Anyone have any ideas what might be wrong? I have gone over this circuit many, many, many times, but can't see anything out of place. repeatedly checked polarity of the electrolytic capacitors.

If someone has a built one, would it be possible to check their supply voltages to the chips around the EQ section? Also put their finger on the 1458 IC (below the Mid EQ level socket), and see if it is also burning hot...

Many thanks in advance

[mc_binc]

Have the board but haven't built it so take this for what it's worth...

JH designed this to run on -15/0V so the negative voltages may be correct.

EQ circuit is not involved in linear/solina modes under normal operations.

The voltage ref scheme (v3, v4) is... okay... if things are functioning. If not, failure in one area may perturb others via coupling in the reference points.

The Low/Mid/Hi EQ circuits are all identical, just different component values. What is shared is a gain/buffer amp which feeds the three EQ pieces. This happens to also be the Mid EQ IC. Best guess is a component or short in the vicinity of U3 but could also be U4.

With the IC making heat, the R77/10ohm resistor should be burning up. Look for heat/damage here as well.

[LektroiD]

HI, thanks for your reply. It is now fixed... Firstly the TL071 was causing the mid EQ opamp to overheat, replaced the 071 and the mid 1458, and now the EQ section working as expected.

Still no audible change between Solina and Linear though.