Peavey DECA 528 info needed

[Mick Bailey]

I've got a Peavey DECA that's blowing fuses. There's no DC on the output on either channel when run on a bulb limiter and no load connected, and the output trannies don't have any shorts, so I'm looking at the PSU side for the problem. Can't see any signs of damage, burning, funny smells, or bulging caps.

The main difficulty is understanding how this works. I've had no luck finding a schematic and the PSU is unfamiliar to me - looks like a switcher of some sort but it's operation is unclear. Before taking it apart I need to understand more about it - does anyone have any information or experience with these amps?

[Enzo]

Certainly someone does, Peavey does. COntact customer service at Peavey and ask for the schematics for your amp.

A burnt up part is easily seen and sure is a sign it is bad, but the vast majority of failed parts don't look any different from good parts.

I don't have the 528 handy, I'll have to download it, but the 700 has a plain old rectifier and filter power supply. You do realize I hope that this entire amplifier is a switcher, it is a digital amp.

In addition to the schematic set, the DECA700 anyways has a service manual as well. A bit of more in depth explanation anfd some service procedures. SO when you contact them, ask if there are any additional materials on your amp beyond the swchematic set. I'll have to find out how similar the 700 and 528 might be.

[Enzo]

Well, looking at the 528, it DOES seem to have a switching power supply, at least in part.

I recommend calling them first thing in the morning. They open 8AM central time. Wait til noon and you'll wait in line on the phone for an hour.

Have your serial number handy.

[Mick Bailey]

Thanks. I've mailed Peavey to get schematic and any support information they may have. I'm in England and phoning would cost me more than the amp is worth!

The main board is identified as 'DECA Power supply BD' and it doesn't seem to be as integrated as more modern digital amps, so I'm hoping it will be easier to work on once I can figure it out.

As they say, though - you live in hope, but die in despair.......

[Mick Bailey]

I now have the schematics from Peavey, but more importantly, perhaps, have the supplementary notes (thanks Enzo, wouldn't have thought to ask otherwise). These give test procedures - more like the 'old school' stuff I used to get repairing industrial equipment in the 70s when manufacturers actually supported field engineers. Wish there were more companies around like this.

[km6xz]

Peavey is the old throwback company that does not know that voice mail and impossible to deal with technical departments/parts etc is the new norm. Even if their gear is not the most innovated or great sounding, we all love the company and wish them well.
Are you sure the ps is the problem? The power amp modules are usually the problem and cause ps shutdown. The switching amp was a bit ahead of its time with a complex controller that now would be a tiny foolproof IC. If I remember correctly, Peavey rebuilt power amp modules for less than parts alone would cost. They can be repaired by Peavey quickly and cheaper than doing it yourself. Pay attention to the ferrite core inductors, if they had high current small cracks would developed which of course completely changes its properties and that is a cause of headaches in pulse circuits. If in doubt over the zeners and inductors, replace the with the Peavey original parts.

[Steve Conner]

Yikes! This sounds like a quirky one from the dawn of Class-D. My first step would be to locate the fault on a module level by disconnecting the amp modules from the PSU. Once we figure out what module the fault is in, we can troubleshoot at the component level (or see if Peavey UK have any rebuilt boards for sale? )

Enzo recommends always checking the rectifier diodes on the secondary side of switching power supplies. I have to say that agrees with what I know about SMPS, those diodes are worked pretty hard, rectifying dozens of amps of high frequency current with so-so cooling. They can fail short, at which point a well-designed SMPS will go into protect mode, but a cheap and nasty one may blow the main switching transistors, which then take out a lot of other stuff in a domino effect. The rectifier on the primary side is worth a check too.

As an aside, the mains fuse in a SMPS is usually the last thing to blow after everything else has cremated. It tends to be grossly oversized to survive the inrush current of charging the DC bus caps, and so useless for actually protecting any of the components. If there are several fuses in the unit, which one(s) are blowing?

Ecologist Garrett Hardin said "You can never do just one thing". In power electronics, you can never blow just one component.

[Mick Bailey]

The Peavey documentation covers the test procedures to determine where the fault may lie. I haven't had chance to properly read through the notes in conjunction with the schematic. The amp looks like its built out of (then) industry-standard components, so I expect the repair to be reasonably economical in terms of parts, unless one of the custom inductors is faulty.

I ran through a basic check of the heavy-current components to see if there were obvious signs of shorting/low resistance anywhere, but couldn't find anything amiss with the usual SMPS culprits. The output stage doesn't show up any shorts and, as I say, there's no DC on the output. My thinking that the fault may lie in the PS is an assumption because of this, but could easily be wrong due to the interaction between functional units. The mains fuse is 4A (240v supply) and there are no other fuses.

Running through the official test procedure would be the next step, at least to narrow things down.

Don't you just love closed loop systems? Either 100% fixed or 100% broken. If I can I'll post the notes and schematic. Pretty large files, though.

[Jazz P Bass]

If I can I'll post the notes and schematic. Pretty large files, though.

Get the program 'Cute PDF Writer'
It's free.
You can 'print' (as a pdf file) certain pages or knock down the file by printing blocks of pages.
That is, if the file is not 'locked'