| 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??? |
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| Netlist |
Hi jitter
Is the amp driven with STK modules for each channel? Which ones?
Is the output relay control a TA7317P?
/Hugo :) |
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| jitter |
The amp has one STK3102IV for both channels and yes, the relay control is a TA317P.
Can you tell me more? |
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| Netlist |
| quote: | 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 |
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| 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... |
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| Netlist |
| quote: | Originally posted by jitter
Like I said, there's only one STK module driving both channels (not one for each).
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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 |
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| 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. |
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| 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. |
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| 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 |
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| 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. |
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| anatech |
Hi Jitter,
Some STK front end chips had a heater to stabilise the DC offsets. This minimizes drift. I'd have to check which ones exactly and this may not apply to yours. Could be my Japanese contact applied a mis - term and meant that the chips were designed to reach a temperature higher than ambient (for the same reason). Since I'll never be able to read the spec sheet, I'll never know for sure.
You are right in that a heatsink in that circumstance would be counter productive. That was my point. Most manufacturers do not use a heatsink on these parts. I wonder if Marantz is pushing the envelope on supply voltages.
-Chris |
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| jitter |
| Sorry for the delay, but I haven't had time to measure the supply voltage before now. It looks like the supply voltage of the STK-module is 56 V. |
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| anatech |
Hi jitter,
My data book for STK3102III gives figures of +/- 75 VDC as an abs. max, with a current draw of 20 - 30 mA at +/- 60 VDC. This means a device dissipation of 2.2 - 3.4 W approximately. The case temperature will greatly depend on the ambient temperature. Your DC offset looks like it is in the 20 - 30 mV range in the stock circuit for Sanyo.
The device is being used at the "target" conditions as specified by Sanyo, so the failure is not due to excessive stress, just normal factors. The failure rates have been higher with these than descrete circuits in my experience.
-Chris |
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| djmiddelkoop |
Hi,
I have repaired 2 PM80 amps here in the Netherlands.
Both amps had a bad STK3102IV.
I noted that all the supply voltages were significant higher than posted in the schematics. This is maybe also the cause for STK failures due to the higher dissipation.
As a solution, after repair, I changed the voltage tab on the mains side of the transformer to 240V.
Now all the voltages were in range.
BTW, I also added a heatsink to the STK module, and it was real cool now. So I doubt that a heater is used inside.
Dick. |
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| anatech |
Hi Dick,
I would tend to agree with you on this one. If a unit has a heater, it would draw more current as it warmed up. Certainly more with a heatsink attached.
We have high voltage situations in Canada sometimes. We don't have a 125V tap though.
Regards, Chris |
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| jitter |
Thank you for this extra info.
| quote: | | I changed the voltage tab on the mains side of the transformer to 240V. |
The design of the PM80SE is heavily based on the PM80, but several components have been upgraded for better sound quality (power transformer now a shielded toroidal item, to name one). A factory-modified model, so to speak, albeit built from the ground up instead of modified afterwards. I don't know the PM80, but my PM80SE is designed for 230 V only. There's no tab to change the mains-voltage.
I think IŽll add a heatsink to the STK-module.
| quote: | | The failure rates have been higher with these than descrete circuits in my experience. |
My brother very recently bought a PM7200KI, also a factory modified model. This model is directly comparable to the PM80SE. Its design seems to have a reverted to a discrete preamp-stage (from what I could see through the ventilation slits).
| quote: | | We don't have a 125V tap though. |
Mainland Europe used to have 220 V and UK/Ireland 240 V. Gradually (in about 10 years or so) this has been evened out to 230 V for all countries. In the old days there usually was a 220V/240V tab. Not so anymore, and despite being 12 years old my amp was already designed to take 230 V |
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| LifeIsMusic |
hello,
I have heard that STK3102IV is possible to replace with STK3102III and STK3152 but still dont know which suits better (lower THD) ...? Some differencies:
STK3102: THD=0,005% if Vcc=+/-50V, f=20kHz, Vo=28,3V
STK3152: THD=0,005% if Vcc=+/-60V, f=20kHz, Vo=34,6V
It seems that older Marantz models like PM80 are better sounding than similar new ones like PM8000, has anyone made a comparsion? jitter? :)
Also wondering if someone could send a copy of schematic of PM80SE or PM80...
Thanks |
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