Peavey 2.6C Question

[Enzo]

If one channel works, then those resistors are fine, they are used by both channels. Your problem is in the specific channel, not the power supply.

[BowerR64]

If one channel works, then those resistors are fine, they are used by both channels. Your problem is in the specific channel, not the power supply.

I didnt bring my meter to check my friends voltages and stuff his is still working with no DDT leds but i dont know for how much longer. His actually looks worse then the 2.6C


One of the filter caps appears to have overheated and the shrink wrap has shrank and the cap has vented already. Its just a matter of time for it to dry and fail.

I checked his and his resistors got hot in just a few seconds as well.

So no one thinks maybe the resistors are overheating the zeners and causing them to break down and change value maybe? im not sure im just guessing. Ill check the voltage on both sides of the resistors.

[Enzo]

No, again: the zeners serve BOTH channels. If they were a problem, then BOTH channels would be acting the same.

[Jazz P Bass]

Whew.

Tilting at windmills?

[52 Bill]

Okay, let's all get on the same page here. First, for now forget about you buddy's amp let's all just concentrate on your problem. We can help with his at a later date. In any case, he has a different amp and it will have different parts and circuits than what yours has.

There should be two resistors that are heating up, not three. They are R141 and R142, 700 ohms at 5 watts. The purpose of these resistors is to help reduce the voltage from the power supply down to the level that the preamp chips need to operate correctly. So they take somewhere around 50 or 60 volts and reduce it down to 15 volts. The two Zener diodes are what control the lower voltage at 15 volts.

So the 40 or so volts that are being reduced from the power supply have to go somewhere, and that somewhere is heat. So the resistors get hot, so hot that they char the pc board underneath them. Sometimes these resistors are mounted up, over the board to help reduce the amount of charring. After you fix the amp, you can go back in and replace the resistors and mount them up and away from the board, or mount them to the chassis or whatever you want to do, but for now let's fix the amp and not modify it until later.

The first step would be to measure the power supply voltages. Set you meter to read dc voltage. Connect the black lead to either the power supply ground or to the chassis and use the red lead to read the voltage at both ends of R141 and R142. Do this when the amp is cold and just turned on and again when the DDT light comes on. Post the readings here. Pay attention to positive and negative readings.

[Jazz P Bass]

I don't know.

I don't really see it as 'charring'.

The fiberglass board is slightly discolored, yes.

How old is the amp?
How much time is on it's clock?

I would let it be.

Really, it does not look all that bad.

[52 Bill]

I would let it be.

Really, it does not look all that bad.

I agree, but it is a concern for the owner. For now I'm just trying to get him to focus on the problem and not on extraneous details.

[Jazz P Bass]

Yup.

Agreed.

[BowerR64]

Okay, let's all get on the same page here. First, for now forget about you buddy's amp let's all just concentrate on your problem. We can help with his at a later date. In any case, he has a different amp and it will have different parts and circuits than what yours has.

There should be two resistors that are heating up, not three. They are R141 and R142, 700 ohms at 5 watts. The purpose of these resistors is to help reduce the voltage from the power supply down to the level that the preamp chips need to operate correctly. So they take somewhere around 50 or 60 volts and reduce it down to 15 volts. The two Zener diodes are what control the lower voltage at 15 volts.

So the 40 or so volts that are being reduced from the power supply have to go somewhere, and that somewhere is heat. So the resistors get hot, so hot that they char the pc board underneath them. Sometimes these resistors are mounted up, over the board to help reduce the amount of charring. After you fix the amp, you can go back in and replace the resistors and mount them up and away from the board, or mount them to the chassis or whatever you want to do, but for now let's fix the amp and not modify it until later.

The first step would be to measure the power supply voltages. Set you meter to read dc voltage. Connect the black lead to either the power supply ground or to the chassis and use the red lead to read the voltage at both ends of R141 and R142. Do this when the amp is cold and just turned on and again when the DDT light comes on. Post the readings here. Pay attention to positive and negative readings.

After a few minutes the B DDT comes on i can flip the DD switch off in the back and it goes out. lol but that doesnt mean its fixed.

Here are the voltages, they didnt seem to change much. I also felt around and nothing else is getting hot when the DDT led comes on, none of the power transistors none of the little 8 pin op amps, and there are a couple 3 pin transistors with heatsinks on em they arnt hot either.



I just checked my friends unit to see if his gets hot like mine, i wasnt sure and his looked worse then this one but his seems to be working just fine.

I wonder though about those big filter caps, since his seem to have been hot i wonder if the one in this amp arnt dry inside and not running at the proper value. His caps are different though, metal top mine have a plastic cover over them.

Thanks again for the help i may actually learn something here!

There should be two resistors that are heating up, not three. They are R141 and R142, 700 ohms at 5 watts. The purpose of these resistors is to help reduce the voltage from the power supply down to the level that the preamp chips need to operate correctly. So they take somewhere around 50 or 60 volts and reduce it down to 15 volts. The two Zener diodes are what control the lower voltage at 15 volts.

There are 4 getting hot, only R141-R142 are burning the board. The other 2 i dont think are getting as hot but they are running hot maybe they shouldnt?

[Enzo]

Bower, friend, STOP.

Those resistors and those caps are NOT your problem with ONE channel dropping into DDT. ANY problem that those caps and resistors cause will affect BOTH channels at the same time. You have only one channel with a DDT issue, so the problem is in that channel, not in the power supply. Seriously, honest.

[BowerR64]

Concentrate on the problem.

As Bill stated, both channels use the same power supply.

If the resistors where an issue, both channels would be affected.

The voltages can be checked right on the cement resistors.
One side of either resistor will be +HV/-Hv & the other will be + - 15 Vdc.
(Consult the power supply pdf that I posted.)

The DDT circuit itself may be at fault.
Try to monitor the output pin (#7) of IC U300B.
It should go high when the DDT LED lights.

[ATTACH]38626[/ATTACH]

Im not sure how to do that, would it be DC voltage? i use my meter to ground then probe pin 7 with my meter set to DC? it uses +5v to opperate or something right?

Also are you refering to U200 or U201? im not sure what pin is pin 7. The little dent on the chip indicates the pin 1 side right? is it the top or the bottom where you start with pin 1?

[BowerR64]

Yeah i know, arnt we starting from the source first and then moving in? making sure the transformer is supplying proper voltage first then moving in?

[Enzo]

Sure, but we determined the transformer and power supply were working many posts earlier.

[BowerR64]

Sure, but we determined the transformer and power supply were working many posts earlier.

ok then what is my next step? i must of missed it

sorry

[Jazz P Bass]

Post #30.