Peavey 2.6C Question

[52 Bill]

My fast test would be to swap the two DDT chips and see if the problem moves to the A channel.

[BowerR64]

My fast test would be to swap the two DDT chips and see if the problem moves to the A channel.

Swap the 2 i have pictured with the 2 on the other channel? That seems easy enough!

[52 Bill]

Swap the 2 i have pictured with the 2 on the other channel? That seems easy enough!

Yes, that might work, but both channel share one chip, U300. You may have to try that one as well.

[BowerR64]

Yes, that might work, but both channel share one chip, U300. You may have to try that one as well.

It has 4 8 pin chips, 2 on one side and 2 on the other, each side are identical. U100 and U101 on the left side and U200 and U201 on the right side. All of them are 8 pin chips.

I swapped em around and tried it with the same results after a short time nothing hooked up just plugged in and turned on the B channel DDT comes on

what should i try next?

[52 Bill]

There are 5 total chips on the board, the four that you have swapped and one more that is shared by both channels, U300. Look at the lower left end of the board that you did not show in this last photo.

Carefully read the voltages on all of the pins of U300, referenced to ground. Looking at the chip with the end notch to the top, the left 4 pins from top to bottom are 1, 2, 3, 4. The right 4 pins from bottom to top are 5, 6, 7, 8. Be careful not to short any pins together with your meter lead. List the voltages here.

Do you have any parts on hand other than what you have inside this amp?

[BowerR64]

There are 5 total chips on the board, the four that you have swapped and one more that is shared by both channels, U300. Look at the lower left end of the board that you did not show in this last photo.

Carefully read the voltages on all of the pins of U300, referenced to ground. Looking at the chip with the end notch to the top, the left 4 pins from top to bottom are 1, 2, 3, 4. The right 4 pins from bottom to top are 5, 6, 7, 8. Be careful not to short any pins together with your meter lead. List the voltages here.

Do you have any parts on hand other than what you have inside this amp?

I dont see the 5th chip, unless its on the bottom of the board or something? this is the PV2.6C? I see a section on the amp where it looks like there could be a spot for it and i see it on the board layout on the PDF file but i dont see it on my actual unit?

Peavey cutbacks?

[52 Bill]

I dont see the 5th chip, unless its on the bottom of the board or something?

I don't see it either. Maybe you can contact Peavey and get the correct schematic.

[Jazz P Bass]

'Peavey cutbacks'????
WTF.

Check the voltages on U300.
That is what drives the DDT led.

[Enzo]

Cutbacks?

You have a "first cut" board version of the amp. The fifth IC was added at the second cut. I have three versions of the schematic in my files. In the older version, yours, the function of the fifth op amp was accomplished by four small transistors on each channel. There is no U300 on his board.

Please note, the four ICs may all have 8 legs, but they are not the same types. There are two kinds, and you can swap them between channels, but you cannot mix which sockets they go in. U100 for U200 and U101 for U201. No other swaps allowed.

[DrGonz78]

Enzo your file is pointing to an old file that got taken out by the server hiccup. Got to zip file it or something...

[Enzo]

Crap.

[Enzo]

Try this:

[BowerR64]

Cutbacks?

You have a "first cut" board version of the amp. The fifth IC was added at the second cut. I have three versions of the schematic in my files. In the older version, yours, the function of the fifth op amp was accomplished by four small transistors on each channel. There is no U300 on his board.

Please note, the four ICs may all have 8 legs, but they are not the same types. There are two kinds, and you can swap them between channels, but you cannot mix which sockets they go in. U100 for U200 and U101 for U201. No other swaps allowed.

Right i looked at the chips before i swapped them, i did see that 101 and 201 were the same as was 100 and 200 so i only swapped those that were the correct number for number.

It did the same thing after a few minutes the DDT came on channel B only.

The cutbacks thing was a joke, i watched an undercover boss on tv where they went to the peavey plant and that was one of the things they did was lay a bunch of people off after they gave a few selected employees funding for things then moved everything overseas.

[Enzo]

Ah, normally my joke radar works well enough...

Straight down from U200b are four transistors in a little balanced arrangement sampling the inputs to U200b through a pair of 820 ohm resistors. That is what controls the DDT. To the left of them is Q208, which actually runs the LED. From under those four transistors comes the line to control Q208. it comes from the couple of 180 ohm resistors and into 47k R235. You have the other channel working right, so use it as a model. Look at R235 compared to R135 other channel. Is the voltage at the base of Q208 climbing until the light comes on? For that matter - no load on the amp please - is there any creeping DC on the output of B channel? Is the voltage coming from the two 180 ohms the same as the good channel?

If the base drive is the same on Q208 and Q108, you might simply have a leaky Q208.

[BowerR64]

Ah, normally my joke radar works well enough...

Straight down from U200b are four transistors in a little balanced arrangement sampling the inputs to U200b through a pair of 820 ohm resistors. That is what controls the DDT. To the left of them is Q208, which actually runs the LED. From under those four transistors comes the line to control Q208. it comes from the couple of 180 ohm resistors and into 47k R235. You have the other channel working right, so use it as a model. Look at R235 compared to R135 other channel. Is the voltage at the base of Q208 climbing until the light comes on? For that matter - no load on the amp please - is there any creeping DC on the output of B channel? Is the voltage coming from the two 180 ohms the same as the good channel?

If the base drive is the same on Q208 and Q108, you might simply have a leaky Q208.

Dude i think thats it!

When it starts cold i get -15 from the center to outer pins on Q108 and Q208 nothing on the bottom pin as it goes the bottom pin starts to climb up till it gets to a voltage to kick the LED on, it starts out very dim but as it goes it gets brighter as the transistor breaks down i think i first start to see it illuminate about -1.5V or so as i touch the R235 and R135 the LED blinks

Where can i order that transistor?

I dont see any climb in voltage on the output of channel A or B i may not be checking it right though. Just trying AC and DC voltage and all i get it mVolts