Peavey XR600 series 400R

[Chaffeekid]

Hey JP, thanks for the pep talk, but like I said, never made a living at repairing electronics, just dabbled in them, you might say, know enough to be dangerous You say the output is conducting, but I have no idea where or what would cause it. I have pulled each of the output trans and checked them, including the two new ones mj15003's that I installed and checked for shorts between the collector and emitter, and emitter to base, all check good.

I replaced the 761's with 2n5401's, and one other transistor. I have pulled one end of the 4003's from the board and checked each of them and all check good on my diode checker. I have pulled the end of the 22 ohm 2 watt and checked it as it is in parrell with the large choke and check as a direct short in circuit, it is good.

Checked each of the 250 ohm, 5 watt resistors, both check good. The 18 ohm resistors and the 4.7K ohm resistors are all good, found one 4.7 ohm resistor blown and replaced it with a 5.2 that I have.

Still have -19 volts on the speaker terms and the EP430 and 431 in the power supply area still get extremely hot as does the two 250 ohm 5 watt resistors. I have replaced the EP430 and 431 with TIP30c and TIP31c. Still have :
1K 5watt resistor .7volt one end, -23 volts on the other
2K 5 watt -1.7 volts one end 53 volts on the other
Junction of the 22 ohm and 4.7K 22.92
Base of 431 +15.92
Collector +23.08
Emitter 15.92

Base of 430 -15.38
Collector -25.15
Emitter -15.38
Sorry to bother you guys with all this, but that's where I'm at with it, kinda stumped.
Jim

[Jazz P Bass]

Any chance you could label some of these components.
Qxx
Rxx
I cannot follow this.

[Chaffeekid]

JP that is the problem with this old amp, there is no layout for it. If you look back up in my posts on this you will find the schematic on the 400R and a hand drawn layout. On the schematic there is no Q# or R# I wish there was might make it easier. I believe that is why Enzo didn't chime in, its just a mess to try and figure out.
Thanks anyhow
Jim

[Enzo]

You all seemed to be progressing, so I didn;t wade in and muddy things.

The two EP430/431 are your 15v power supply regulators, and it is normal for them to get hot. They seem to be producing the desired voltages.

SO you have 19v on the output. I suspect them that the output stages are fine, they are just being directed to put the 19v there.

let me number your parts: Look at the schematic for the 400R. The power supply is in the lower right and seems to be working, so let us ignore that part.

I take that back, dod we determine yet that BOTH 50v rails are up to volts and clean?

Assuming so... look at the output on the right. There is a line back from the inductor to the left almost all the way across, that will now be the centerline and we can refer to top and bottom half. SO start at the left, and number the transistors left to right across the top half. Q1, Q2 are the 761s, the 3642 is Q3, and so on to Q8, the upper right corner output guy. Now back to the left end of the bottom row. Q9, Q10 are the pair of 430s, and so on to Q16 the botom right output.

There, frames of reference. Looking at your layout hand drawing, I can make some guesses, but you can fill in numbers on that when you ident each part there.

-19v on the output tells us that both sides are not turning on at once, so I will guess all the output bases are at roughly -19v. The yop row maybe only at -18 and the bottom row maybe at -20, but all close. There is that one diel diode, the 13886, on the heat sink with wires back to the board, that is just left of Q3 on the drawing, and below it is the 1N4148 with 18 ohms in parallel. I bet you have the -18 on the top end of the 13886 and the -20 on the bottom end of the 4148. Or whatever, something within a couple volts of -19. Yes? No?

The way the amp works is, those diodes keep a steady space between the upper bases and the lower bases. Then the output follows whatever is on them. Q10 down there moves that whole thing up and down with the music, and Q1 controls Q10. Q9 and Q2 are feedback.

Now this schematic is chock full of test voltages. You need to check them. Look left of teh 13886 by Q3. See 1.1v between the top end and the output ? Is it? The output may be -19v, but is that point 1.1v more positive than that? Likewise the 4148 next to Q11, got about 0.6v across that?


I am bettting the collector of Q10 - the tab - is at about -20v, and so us controlling the output. The emitter of Q10 has an 18 ohm resistor to V-. Now look left from Q10 base, lower left of drawing is another 13886 connected to that base. To the right of it is a cap with 1.1v across it. The cap isn't the issue, that 1.1b is from the base of Q10 to V-. Is it ther?

Look upoper left, a 50uf 50v cap has +48.6v on it. Does yours? From there down through a 22k resistor to Q1,Q2. Should be 0.07v there, is there?

[Chaffeekid]

Hey Enzo, that info will sure load my wagon I will label those parts and take some more measurements and let you know. Have put the amp back together so will have to take it apart again. Printed out your instructions and will let you know what I find. Ordered two of those 13886's from peavey and received them yesterday just on a gut feeling. Hope I'm right

Thanks again
Jim