FW-1082 Noise/Power Supply Overheating

[Gerald Prokop]

I have been futzing with my 1082 for weeks trying to get rid of a noise issue. I replaced the input, output, and preamp boards completely (I bought a salvage unit years ago) with no change. I replaced a capacitor on the power supply board (c23, it was one of the fixes on this forum) which seemed to help, but then I noticed the heatsinks on the power supply and on a nearby cap are getting very warm. I started blowing a big fan at the power supply board everytime the noise starts and it goes away in a few minutes and the preamps are dead quiet. I replaced the PQ3RD13 IC and redid the heatsink grease on both heatsinks. It's a little better but still gets the noise, especially with phantom power applied.

The noise is kind of an electronic whir that wavers slightly with frequency. It's not hum like 60hz mains and it's not hiss. I would say low mids to mids. I have sound sample but don't have permission to add it. The noise is affected by the faders and the output pots (main and phones) It is not affected by the gain/trim pots. It is only when the track is armed, and it does end up on the recording. It is there when the cables are plugged into the inputs and when they are not.

If it matters, I am going into Reaper via a PC.

I could certainly keep guessing, solder sucking and swapping. The parts are cheap enough. But does anyone have an educated guess? I'm not into repeating damage by troubleshooting in the wrong order. My inclination is to get that other IC that has a heatsink on it (IC2, 8050S), as well as that hot capacitor that is nearby (2200mf, 2nd largest on the board).

The power supply is HQRP replacement 12v 5A

Thanks in advance for any guidance.

 

[Gerald Prokop]

Update: the noise is still there despite replacing the 8050S as well as the PQ3RD13 and several of the largest capacitors.

I talked to a tech at a certified Tascam repair shop who told me that the power supply would overheat if another board was drawing too much current, so I started swapping out boards. The only ones I didn't try swapping were the ones that merely house encoders and buttons, and the big main board. The "spare" main board I have is faulty.

So there is one of two likelihoods: 1. Something on the power supply board is bad and overheating, which I could continue to hunt down, or 2. the main board is drawing too much current.