Peavey XR696F cap issues

[Mick Bailey]

I've just had another 4 of these mixer/amps in - three of them NOS in sealed boxes for checking prior to re-sale.

The three boxed units produce about 2W each (absolute max) and the FX modules don't work. Upon investigation, every single SMD electrolytic reads open on my ESR meter. Many have crusty patches where they've oozed and dried. All of the leaded components are fine.

Maybe something to check if you get one of these in for repair.

[J M Fahey]

Ouch!!!
And *weird* , that shouldn't happen, they're not that old, less than 10 years definitely.
Were they pulled from an abandoned container sitting in the Sun for 10 years ?
Did you pull a few random caps, here and there, to measure outside the circuit?
Or if they show any capacitance at all?

Weird.

EDIT: have you checked your meter?
Such massive failure looks *so* unlikely

FWIW Musician's Friend still lists them, although unavailable, so they were there in the last few months.
Somebody posted here about repairing one of them short ago ..... or maybe in SSGuitar.

[Mick Bailey]

Checked every one in-circuit and pulled quite a few to check on the bench. I check my ESR meter every time and always zero it with the probes shorted before use. Some measure OK for capacitance, others in the pF range. Some of the 10uf/16v completely crumbled under finger pressure.

There are a few that start out at several hundred ohms ESR and then quickly rise off the scale.

All of the amps get a reasonable dry signal at the output of the mixer stage and I can scope this at the other end of the ribbon cable where it plugs into the power amp. Then it disappears at the other side of the 47uf coupling caps.

This reminds me of some Takemine preamps where every SMD electrolytic goes open, leaving no output whatsoever.

I've just ordered a complete set of caps with the intention of doing one amp first to see how it goes. Being SMD the parts cost is fairly low, but what a dreary task.

Strange.

[J M Fahey]

Ok, just checking.

Not the first time a hard boring task is carried, and then it's: "oh no!!!! meter batteries were flat and I misread !!!!"

Please state brand and values involved, obviously a bad batch which bit Peavey in the leg and might show up in other brands/models approximate same era.

I remember the "bad electrolyte formula" problem which hit almost all of the Motherboard Industry worldwide a few years ago, maybe there's where the last bad caps ended.

A couple pictures would be fine, specially showing oozing and the one crumbling between your fingers.

[shudder]

[The Dude]

I can smell that repair from here!

[Mick Bailey]

Here's how some of the caps have ended up. I noticed the fan trays have some corrosion too, so thought that they may have been badly stored. So I checked another amp that wasn't part of this batch (and has been in regular use) but which has one channel that's much quieter than the other. Turns out the low channel has faulty caps.

I'd already chucked the crumbled caps, but you can see the how badly some are corroded - you can see the cap winding inside the can on this one



The affected caps are:

All 47uf/35v
All 10uf/16v
All 1uf/50v

They're the same caps on the FX module and power amp. The 2x1000uf caps on the FX module read about 30 Ohms ESR, so are on their way out too.

I haven't lifted the mixer sections from the front panel. There's good signal output from all of them. A peer with a torch down the gap between the board and panel looks like the caps are through-hole. At least, all the ones I can see are. I'll renew the caps on the power amp and FX board and see how they go.

[Mick Bailey]

Just done the first one and it's 100% fixed the problems. These are now on my 'least favourite' list.

[J M Fahey]

Ouch!!!
I would never ever had believed that an electrolytic cap electrolyte would be so active and the wrong way, strong enough to eat through the can cap wall
Incredible.

[Leo_Gnardo]

Ouch!!!
I would never ever had believed that an electrolytic cap electrolyte would be so active and the wrong way, strong enough to eat through the can cap wall
Incredible.

The electrolyte is sodium hydroxide mostly unless they've "improved" on that. These failures speak to a failure to design/build a container impervious to the corrosiveness of the electrolyte. "Aw build it cheap, they'll never notice."

[Mick Bailey]

I adopted a better technique than desoldering: Snip right through the can with sharp side cutters, pull any remaining rubber/plastic away and trim the connections before removing the base pad. Then flux and desolder braid to clean off the pads. All of the caps had leaked underneath - some were wet, most had brown or grey crystals. I checked each one before removing to make sure they were all faulty.

Three amps now done and all working fine.

I wonder if the caps have a poor formulation? The other thing that protects the can from corrosion is the heavy anodising. I'm unsure about the construction in an SMD cap - would the electrolyte contact the can anyhow, or be trapped within the actual winding structure?

[J M Fahey]

The electrolyte is normally in contact with the case, which in fact *is* connected to negative, and zillions of caps in use since forever show that it does not eat through the case metal.

In fact, open any junk electrolytic you have around and you'll see the unblemished internal surface.

That said, a few years ago there was a "bad electrolytic" pandemic running all over the World, apparent culprit was some "new-improved" formula which obviously failed, worst hurt were Motherboard manufacturers..

FWIW Zombie Apocalypse will start the same way, and I'm only half kidding

[Mick Bailey]

I frequently unpack can-type caps to re-stuff them with smaller, new components. Just to preserve the appearance in some vintage amps. Even the oldest amps rarely show any sign of corrosion inside. That's after 40 or 50 years. So for an amp to fail after just a few years is pretty disappointing.

But, we're caught between rapid changes in component technology and cheap manufacturing where price is the dominant force. When looking at component prices there's sometimes more than a 10:1 ratio between unbranded and branded components of the same type and specification.

[Mick Bailey]

Yet another one of these - this time with a high-pitched whine on both channels and a lot of rustling noises. Applying a finger to the FX pcb changed the pitch dramatically and reduced the noise. I checked the caps and most are high ESR and some completely open. I started to mark the open ones in red, but gave up because they all need replacing.. When I removed the board I could see gel oozing from two of the caps and all the solder connections are corroded. So, another for a re-cap.

[blindboybenton]

Hi Mick

Just reading this post. Ive got one with a odd and similar fault. Due to the design ive stripped it down and now im busy put it to one side for a couple of days
Dont remember if the effects are working or not.

Quick question.. Did replacing the caps on fx board ( as stated further down ) fix the max 2watt problem ???

My caps all look fine but it does have a odd fault. .. Possible something wrong with the mute circuit is my first thoughts

many thanks

BBB

[Mick Bailey]

Take a real good look at those caps and if possible do an ESR check. I've since had another two of these amp with exactly the same issue.

The main signal restriction was the electrolytics on the power amp board. These are the same SMD type as fitted to the FX boards. I replaced all the SMD caps on the power amp board - these are fairly accessible. If you do a check on either side of the 47uf coupling caps you may see the signal on one side of the cap and not the other.

The FX board fault mainly contributes to unwanted noises - even with the FX level turned right down.