Peavey XR684F mixer problem

[Dehn]

Hi Everyone,

Have been working on a XR684F mixer, the problem is in the 400SC power amp.
First, I can't seem to get the right schematic, Gene at Peavey has sent me everything he's got, but mine is different. All the schematics have 2SC3281 and 2SA1302 output transistors, mine has 2SC5200 and 2SA1943's. Printing on the board says: 400SC, 98873032 021599 GWG/FJE PEC 1998.

The problem is the 2SC5200's get hot as soon as power is on, the 2SA's stay cool. The neg 60v supply is -59 volts but the pos supply reads only 50v.
Since all the 5200's are hot I'm thinking something common to both sides.
I pulled the filter caps and checked them. (Tested good) and swapped them when I put them back. I replaced the bridge rectifier too. Same problem.

Does anyone have a copy of the right schematic out there? I really hate to waste any more time till I get the right schemo.

Regards,
Dean C

[Enzo]

Aside from the part numbers for the output transistors, does the schematic set seem to match your board? Those two sets of transistors are similar, and one set could be substituted for the other in this amp.

I have 400SC drawings for versions from 1998, 1999, 2001, 2005. They are all VERY similar.

Since your NPNs get hot immediately, your +60 is probably being loaded down to 50. Are your +16v rails OK?

Are you working with a load? get rid of any speaker load until the amp settles down.

Is there any DC offset on the affected channels?

[zero cool]

I see the C3281/C5200 swap all the time in amps. seems to be a common thing.

I just fixed a XR684F mixer that had the same problem. replace the 3080's and the op-amps, check the J-fets. this fixed mine!

[Dehn]

Peavey XR684F update

Thanks Enzo,
You are right, looks like just the outputs are different, strikes me as funny that there is nothing in the schematics stating this could be so. I figured Peavey changed outputs somewhere along the way and there would be schematic with the different output transistors. We live and we learn.

Regards,
Dehn

Thanks to Zero Cool,

I think your amp and mine have the same problem, I switched around the IC's and now the A's are heating and the C's stay cool. Will order parts from Peavey on Monday.

Thanks for all the input!
Regards,
Dehn

[Enzo]

You may know, but you cannot order from PV by email, you must call. I recommend highly you call them first thing in the morning when they open - 8AM central time.

Ask them also to send you their semiconductor cross reference document. In fact search this forum for it. I don't know if they have that particular sub listed, but many parts show several alternate part types for many parts. If you do much PV work, it is handy.

They won't bother to put out new schematics to show alternative equivalent parts, mainly because the circuit hasn't changed. I suppose they could print "(or equivalent)" next to each part.

Another common Peavey discrepancy is the 400 ohm resistor in between plate and screen supplies in their tube amps. SOme are indeed 400 ohms, but many time you find a 390 ohm inside the amp. 400 is what the schematic specifies, but that is an odd value, while 390 is a standard resistor value. Since it doesn;t matter, it is only a 2.5% difference, well within a 5% tolerance, if their source of 400 ohm parts was out of stock, they could just use 390 ohmers from any supplier to keep production flowing.

If they tore down my house and built a different one there, the address would be the same. Yes I know that is a useless analogy, but I did enjoy writing it.


Old QSC amps - like the 1400 - used to have a row of 2SD424 outputs. Then those were discontinued, so they sent the later amps out with MJ15024 instead. Nothing else needed to change in the amp. Later publications did reflect the change, but one could just as easily replace all the MJ15024 in a newer unit with some 2SD424s. Niether part is wrong. And much as I hate NTE crap, one could find this amp with NTE whatevers stuffed in it. Circuit remains the same.

[Dehn]

Thanks

Peavey parts arrived and amp is running smoothly.

Thanks for the help Enzo and Zero Cool.

Regards,
Dehn.

[ogeecheeman]

hi folks.new to the thread.anyone hear ever experience this XR684F act like this; at turn on - fan begins to run immediately power light flickers but does not stay on.it's as if the unit is on but no 16v to the mixer board. a direct test signal to power amp in gives a wave output that is flat on one side...left and right channels look the same.I do have 16vdc on the ribbon from power supply to mixer

[Enzo]

Hi, and welcome.

Please start a new thread for your mixer, it gets confusing when we talk about two amps in the same thread. Plus you will get better response with a new thread instead of tacking on the end of a thread that has been dormant for seven years.


Do you have BOTH +16 AND -16 on the mixer panel?

[ogeecheeman]

enzo-sorry man I am lousy at this forum stuff. when I last posted the administrator info said I didn't have permission to start a new thread. found the issue.of course you were right on it.3vdc at output of 7815a regulator. associated diodes, resistors and caps seemed fine.evidence of excess current draw at 7815a (darkening of board at pin 2). part on order. concern now is what caused the failure. 7918 is fine

[Enzo]

Oh, when you first join, your first couple posts are moderated, just to make sure you are a human. You should be able to start threads by now.