Denon PMA-520 Amplifier (Not AE). Need repair advice on replacing capacitors.

[Parzival I]

I have a Denon Integrated Amplifier PMA-520 (circa 1989/90). It is not the AE model. The amp is producing pops and crackling sounds, especially on initial music startup, but continuing throughout play. This happens in both the speakers and through headphones, and regardless of input source or channel (phono, CD-direct, aux…).

Any thoughts as to possible causes of this? Is this something I could conceivably repair myself? Or have repaired at all?

While the amp has always been in a room temp, low moisture environment, and never been roughly handled, I’ve never done anything in the way of maintenance.

Thanks for any help anyone can give!

 

[gibbsy]

Welcome to the Forum.

It's an old unit and more than likely needs a little bit of love and a damn good service. Pops and crackles usually mean that some of the caps need replacing. It's probably a case of looking at the insides, first and foremost get rid of the build up of dust and look for any discolouration of the circuits and mishapped capacitors.

If it's beyond you then seek advice from a reputable repairer and ask for an estimate. It may very well be beyond financially viable to repair and the money best spent on a new unit.

 

[Parzival I]

Thanks!
I think I can at least crack the case and have a look around, though replacing the capacitors is indeed probably beyond me.

 

[Parzival I]

Case cracked. Dusty in there.
Most everything looks good to the eyeball, except the four large capacitors near the big round power supply (I assume it’s the power supply; only thing that looks like one). The capacitors are labeled 56v 5600µF(M). Although the tops are fine and the sides aren’t bulging, all four have some dried light brown “foamy” looking gunk at the base, which I doubt is glue.

So, what would be involved in replacing these?

 

[gibbsy]

Stick a photograph on to confirm but that's does look like a classic sign of failure. Can't help with how to change them, I'm not dextrous enough nor knowledgeable. Hopefully someone will be along to help.

Edit your title to reflect that you need help.

 

[Parzival I]

Good advice. Thank you:

Here’s a shot of the really big capacitors:

You can see the dried gunk at the base of two of them; the other two have similar dried gunk at their bases on the opposite sides,

I need to know:
1.) How to discharge these if necessary,
2.) How to remove these
3.) Where to find suitable replacements (so far searching for the labeled description of 56v5600µF(M) turns up no examples of the same capacitors, even from Chemi-con who original manufactured these.)
4.) How to install the latter.

 

[JayCee]

Pretty sure that “dried gunk” will just be potting compound applied when new to stop physical vibration and movement of the caps.
if you still plan on replacing them these should be suitable replacements.

CAP ALUM 5600UF 20% 63V SNAP | eBay

Ripple Current @ Low Frequency: 3.22A @ 120Hz. Ripple Current @ High Frequency: 3.864A @ 100kHz. Mounting Type: Through Hole. Surface Mount Land Size: -. Tolerance: ±20%. Part Status: Active. Lead Spacing: 0.394 (10.00mm).

www.ebay.co.uk

 

[Parzival I]

Thanks. So maybe they’re not bad. That would be great, actually…

Honestly, looking at the board I can’t see anything visually wrong with any component of it. None of the smaller caps show any sign of damage (no bulges, etc..) And the whole thing works, it just adds unwanted noise.
Next step, a good cleaning of the pots.

From the looks of things, I’ll need to remove the front panel to get at the pots. I don’t see away to access them from the back. (Here’s a shot of that):

Most of the pots are hidden by boards; only the main volume pot has any exposure (first photo, far left).

 

[password1]

To be honest these amps can be bought very cheap and it's probably beyond economical repair to send it off. A professional amp repair/servicing guy will have all the necessary equipment to diagnose, find any further faults or worn parts, clean and fully test everything and you usually get some warranty. DIY is only recommended if you know what you're doing. Personally I'd rather not rely on guesswork and potentially risk fire, etc.

You should weigh up the cost of buying a used working amp (and selling your existing amp) and the cost of buying the parts and doing the repair and servicing yourself.

 

[Ascotbilly]

@Parzival I - Did you get anywhere with this ?

 

[Kapkirk]

The pops and crackles you describe will most likely be dry joints and not necessarily the capacitors.
However I would still replace ALL electrolytics on the board as the unit is fairly old depending on how into the renovation you want to go. The problem you might have though is sourcing all the components.
If you do decide to go ahead, once you get the main board out it should be pretty straight forward, replace 1 at a time and make a careful note of the polarity (black line is -) The brown stuff at the bottom of the large caps are a type of glue installed at the factory to stop resonance and secure a better fixing. You can use a little Gorilla glue on the side/bottom when re-installing.

However before going to the expense and trouble replacing all the caps I would re-solder every single joint (especially the ones under the large heatsinks which hold the power transistors in) by holding your iron on them until the solder melts then add a little fresh solder, shouldn't take more than half hour if you are proficient at soldering. Doing this first is FREE and may cure the fault.