Peavey XR600C slow power up - any pointers appreciated

[Toby]

Hi I've got a beaten up Peavey XR600C that I'm going to give a bit of an overhaul to. Change a couple of broken jack sockets and repair a mic channel and reverb tank that's not working.
The last two times I've switched on my amp to use, the power is slow (2 - 3mins) to illuminate on the led on the front.
I have a copy of the circuit diagram (400BH module) and want some help to diagnose which are the most likely culprits to check in the power supply that could cause the "soft start" type symptom?

I understand that I will need to discharge caps before removing high volts parts that may still hold a charge and will handle safely(been a long time since i last diagnosed a crt and could use some help!

Is it likely to be C31,C32 being held low? Or more likely to be poor regulation from VR1,VR2?

Any help is much appreciated, the amp is a robust old beast and, if I can, I'd like to keep it live a bit longer.

[Enzo]

First, identify the problem. Does the amp refuse to amplify before the light finally comes on? or does it amplify right on, except the light stays dark? Don't assume the voltage supply is the problem until your meter says so.

We don't assume something is faulty, then throw parts at it hoping we were right. We find out what the actual problem is, then repair the cause of the problem.

Get out your volt meter, I think you will find the main filter caps discharge in just a few seconds on their own from their 52v.

400BH is usually the power amp on the rear of the XR600C, but is that in fact the board you have?

It would be helpful when you mention a part like C31 and C32 that you mention where it is. It just took me 10 minutes to find them on the power switch. Being "held low"? Those are right on the mains wiring, If they were holding the entire amp at low voltage, they'd be on fire by now.

The power light runs on +15. I think the +22 on the schematic is a typo, there is no +22 coming onto that board. If you think the +15 is coming up slow, stick your meter on pin 2 of the 6-pin connector for the cable between preamp and panel amp. it either comes up to 15v in a second or it doesn't.

And before you decide any component is bad, check the solder under it.

[Toby]

Thanks Enzo
I appreciate your help. Like I said in my previous message it has been a while and that I need help in diagnosing this problem before replacing parts. So Thankyou firstly for your response. You are the Peavey man from what I've read on here!
I can confirm that it does not amplify straight away.
It does nothing for a good couple of minutes and then is fully functional. Hence the soft start description I used. I wrongly assumed it would be related to a mains supply so thought as the fault seems related to a supply with a slow rise it may be a capacitive problem but thought it prudent to ask an expert like yourself as you know more about these amps than I do, clearly. But also why I had ruled it out being the led.
I'm good at soldering and visually inspecting the solder joints. I wanted to just see if anyone had had a similar problem really and which area of the circuit that I need to look in.
I will visually check for anything obvious on the pcba first.
Then I will check the 6 pin connector to start with then.
Hopefully it is just a loose wire or poor solder joint as you have suggested.
I didn't want to tear it down without being pre armed with the area I may have to delve into a bit deeper.
Please don't misinterpret my method/ignorance with anything but that.
Many thanks
Will keep you posted on progress!

[Enzo]

Look lower right on the front panel, the patch jacks. Plug your signal into the power amp in jack. Now we are just hearing the power amp. Does that come right up, or does that take the 2 minutes?

Move your signal to the graphic in jack, same question.

Likewise, plug your ssignal into a channel input like usual, and connect the MAIN out jack to some other amp for a listen. That is the preamp signal. Does it come right up or is it delayed? We need to decide which section of the amp has the problem.

[Toby]

Thanks Enzo
Much appreciated
I will do this, it may take a while though, as once it starts functioning normally (mic input, aux inputs, main out etc) it then powers up and down as you would expect, at a flick of the switch!
It is stored at a reasonably controlled temp and humidity.
All solder joints, components, pcb surface and wiring appears ok and is continuity checked, so no signs of overheating.
I have visually inspected and continuity checked the drive board/pcb and power board/pcb
I've yet to visually inspect and continuity check the master board and the channel board
It has happened on two occasions while setting up for a school disco, as you can imagine I panicked fearing the worst, but then it burst into life and worked in its usual and robust manner! It was a relief to be honest, as I leave work with only half an hour to spare to arrive and setup before they arrive and with no time to realistically source a backup. (Last time I had a friends pa head/amp in the boot just in case)
Will check and report back.
Have a good Easter break

[The Dude]

It could simply be intermittent switching jacks themselves. Read this thread.

http://music-electronics-forum.com/t28549/

[Toby]

Thanks to the dude
Will get some switch/contact cleaner for the ins and outs and some isopropanol for pcb cleaning just in case!
Cheers have a good Easter break