Peavey Studio Chorus smoking resistor

[Logman]

I have aquired a Peavey Studio Chorus 210 that I would like to attemp to repair myself. I have basic electronics experience, and wonderd if anyone could give me a few pointers.

First off, I was given this amp because it was not working. I plugged it in to get a grasp of what was or wasnt happening with this thing. As soon as I plugged it in, smelled something hot. Upon taking it apart, I found resistor R167 (according to the Peavey schematic found online) smoking whenever the amp was turned on.

If anyone can give me an idea where to start testing this thing I would be appreciative. If you think it should hit the garbage can, by all means say so.

If any further info is needed, I will provide that asap.

Thanks !

[Jazz P Bass]

Here is the schematic
http://music-electronics-forum.com/a...s-210-1990.pdf

Could you kindly share where R167 is?

[Logman]

First page, directly above B1 in the schematic you provided.

[Jazz P Bass]

R167

Found it.
If R167 (which is a 22 ohm 1/4 watt resistor) is smoking, then something is demanding more than 1/4 watt of power.
R167 current limits the +15 volts going to IC U9, U10 & U11.

Check to see if any of the ic's are getting hot.

There is a chance that C160 (220uf/25V) is shorted, leaky.

[Logman]

None of the ic's are getting hot. What is the best way to test the capacitor ? I have a DVOM , if its possible to check it with that.

[Logman]

I take that back. U4 on the other end of the board is getting hot.

[Logman]

I see this (u4) is a 4558 op amp. Should I start by replacing this ?

[Enzo]

Op amps that get hot are almost always bad, so even if this one is not part of your original problem, you should replace it anyway. And if it winds up fixing the rest of the issues, then amen to that.

[Logman]

Thank you for your advice. I would really like to get this repaired.

[Jazz P Bass]

The smoking resistor, does it measure 22 ohms even tho it smokes.
Does the Chorus work?
The reason I ask is U9, U10 & U11 are ic's for the chorus.
U9 is a Bucket Brigade delay line chip. MN3007
U10 is a clock generator. MN3101
U11 is a 555 timer chip.
These (3) ic's are fed by that smoking 22 ohm resistor.
Not much else.
Maybe pull U9-U11, one at a time. to see which one is pulling the excess current.
If you have to order the 4558 chip, then I would order these three also.(U9, U10, U11)