intermittent amp problem (PM80SE)

[jitter]

Marantz PM80SE.

Here's the problem: sometimes the right channel starts popping very loudly like suddenly DC appears on and disappears from the loudspeaker output. Then the speaker protection circuit kicks in and mutes the speakers for a few seconds.

Extra info:
- the problem can stay away for weeks and then return regularly;
- volume-setting has no effect on how loud the pops sound,
- selected source makes no difference;
- makes no difference if amp is warm or cold;
- class A or AB makes no difference.

Done so far:
- I resoldered every solder join;
- I soldered the PSU wires directly to PCB of the power amp (bypassing the flimsy looking connectors, one of which showed signs of sparks).

So far this has not solved the problem. And tracing the problem is very difficult because when it occurs, it's brief and it can take weeks to resurface... When the amp works, it works perfectly.

Anyone had similar problems???

[Netlist]

Hi jitter
Is the amp driven with STK modules for each channel? Which ones?
Is the output relay control a TA7317P?

/Hugo

[jitter]

The amp has one STK3102IV for both channels and yes, the relay control is a TA317P.

Can you tell me more?

[Netlist]

Originally posted by jitter
Can you tell me more?

I like to be a little mysterious at first.

Here's what I have:
The STK3102 is probably the cause. You could 'easily' swap them and see if the other channel misbehaves.

The TA7317P is known for frequent failure. Look for brown areas on the PCB and bad 1W resistors in the neighborhood.
This is only in case the relay fails to work.

/Hugo

[jitter]

Until I get a replacement STK3102, I can't swap. Like I said, there's only one STK module driving both channels (not one for each).

Would it be possible to increase the lifespan of the STK-module if I improve heat dissipation?

The relays can be operated, so the TA7317P should be fine.

Thanks for the info, and BTW, I bought this amp secondhand in Belgium more than six years ago...

[Netlist]

Originally posted by jitter
Like I said, there's only one STK module driving both channels (not one for each).

My mistake...
Anyway, if you want to know for sure you'll have to replace it.
About lifespan: If the amp is always driven at full capacity, I would recommend bigger heatsinks. No need to change them for normal use IMO.

Here's the Philips part number for the STK3102 IV:
482220973453
Unfortunately, it will be hard to find.

/Hugo

[jitter]

Thanks again.

The STK-module is used as a pre-amp module in the PM80SE, the speakers are driven by eight BJTs (C3182N and A1265N). So forgive my ignorance, but how could amp load affect a pre-amplifier?

Pre-amp or not, the module gets pretty hot (too hot to touch) in normal operation despite the fact that there is a (small) heatsink.

Fibra - Brandt (Germany) has STK3102IVs in stock (www.fibra-brandt.com) at a very reasonable price.

[jitter]

The new STK-module has taken the place of the old one and I'm happy to report that the problem has been cured.

[anatech]

Hi Jitter,
Glad you found it. Do not heatsink the STK driver chips, some have a chip heater to stabilize them. Putting a heatsink on it would make it work harder. I've replaced several STK drivers for the same fault.

I had a Marantz int amp with the same fault. Darn thing was discrete and I never did find the fault. Same symptoms you had. Yup, resoldered, changed transistors and caps. No joy.

-Chris

[jitter]

If the STK3102IV has a chip heater, why would it have been equipped with a heatsink by Marantz? My reasoning is that if it needs a chip heater, it wouldn't need a heatsink, if you know what I mean.