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Arcam Alpha 10 overheating issues
Arcam Alpha 10 overheating issues
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Old 17th March 2014, 09:51 PM   #1
XsamuraiX is offline XsamuraiX  United Kingdom
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Default Arcam Alpha 10 overheating issues

Hi... I have a Arcam Alpha 10 integrated amp...

The problem is, when I turn it on it just displays on the front panel "Fault overheat" you can clear the fault message but no sound, the speaker relay does not engage so, I bought a multi meter and checked the Transistors, 2 were bad and the thermal pads (non silicon) have NO thermal paste on them, so, was wondering to, replacing the bad Transistors and buy new thermal pads, but use a tiny bit of thermal paste behind the Transistor, all would be ok?
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Old 17th March 2014, 09:53 PM   #2
XsamuraiX is offline XsamuraiX  United Kingdom
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A picture of the pads, all 4 have come away from the heat sinks... They look like they have been in a serious battle, look old...
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File Type: jpg Picture 70.jpg (752.0 KB, 187 views)
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Old 17th March 2014, 10:34 PM   #3
Bare is offline Bare  Canada
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A bit of white thermal goop on their replacements is certainly going to be useful.
How can they have come away.. these are under spring clip pressure.. are they not?
That droopy bit is likely the thermal conductor sheet or facsimile
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Old 17th March 2014, 10:40 PM   #4
KatieandDad is offline KatieandDad  United Kingdom
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Silicon pads shouldn't have thermal paste on them. Despite you saying otherwise, those are silicon rubber pads.

They do get a bit tired in time, that is not the source of your problem.
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Old 18th March 2014, 12:51 AM   #5
Ian Finch is offline Ian Finch  Australia
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In the previous thread, you posted:
Quote:
.....Would it be worth to just not replace them thermal pads and use just good quailty thermal paste, like Artic Silver5?
Don't even think about it. Such metal containing pastes are more thermally conductive alright but also electrically conductive. They are intended for computer CPU coolers which fit to the chip's insulating plastic body - not the metal collector face of a power transistor. Whilst you can, with care, avoid shorts by careful application, its a bad idea to introduce that stuff into your amplifier.

The wrinkling of excess silicone rubber sheet has little to do with the job of insulating between the transistor and heatsink. As long as the clip is firm and sandwiches the transistor and silicone rubber where it matters, it will be fine, as designed. Your problem of overheat sensing is not caused here, because the sensors are mounted under each heatsink. Logically, if the thermal pad (silicone rubber) is not doing its job, the overheat sensing would operate later rather than sooner, if at all.
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Old 18th March 2014, 01:17 AM   #6
XsamuraiX is offline XsamuraiX  United Kingdom
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That's the thing, the pads feel like plastic, not silicone (with that squashy feeling) there is 4 Thermistors, 2 by the power supply socket and 2 by the PSU.... When I read the Transistors values with a multi meter, when there should have been a open line, it was reading current, 3 of them were doing this, but the 4th was ok, all the caps are ok, no swelling etc etc and only 1 resistor is reading slightly bad...

On the service manuel, I can't see any heat sensors under the heat sinks.... Btw, the Transistors are held in to place with clips and the power caps are fine also... Just baffled here
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Old 18th March 2014, 01:22 AM   #7
XsamuraiX is offline XsamuraiX  United Kingdom
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Quote:
Originally Posted by Ian Finch View Post
In the previous thread, you postedon't even think about it. Such metal containing pastes are more thermally conductive alright but also electrically conductive. They are intended for computer CPU coolers which fit to the chip's insulating plastic body - not the metal collector face of a power transistor. Whilst you can, with care, avoid shorts by careful application, its a bad idea to introduce that stuff into your amplifier.

The wrinkling of excess silicone rubber sheet has little to do with the job of insulating between the transistor and heatsink. As long as the clip is firm and sandwiches the transistor and silicone rubber where it matters, it will be fine, as designed. Your problem of overheat sensing is not caused here, because the sensors are mounted under each heatsink. Logically, if the thermal pad (silicone rubber) is not doing its job, the overheat sensing would operate later rather than sooner, if at all.
That is a point, but when it's switched on from a "cold start" the message is displayed straight away, no time for anything to heat up...
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Old 18th March 2014, 02:06 AM   #8
Ian Finch is offline Ian Finch  Australia
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Exactly, and that's why poor hear transfer wouldn't cause your problem. Yes, siicone rubber is like that.

The schematic titled "Alpha 10 power control" in the service manual, specifies two 8-pin heatsense ICs, LM56C1M, as mounted under the heatsinks. I can't prove their existence or not in your amplifier but I assume these are just tiny SMD devices flat on the PCB like any other.

BTW, being power Mosfets, I should have referred to the metal face as also the Drain, not Collector.
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Old 18th March 2014, 09:32 AM   #9
XsamuraiX is offline XsamuraiX  United Kingdom
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Hiya Ian.... I'm only a amateur sad to say only know "some" basics... Should I take just 1 heat sink off? Then I can see what is under one... The service manuals are hard to read to me
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Old 18th March 2014, 12:40 PM   #10
Ian Finch is offline Ian Finch  Australia
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There's no problem with being an amateur, newb or expert even. You're very welcome here as a DIY audio guy. Don't be discouraged by replies that come across as weird, dismissive or over-technical. There are people of a wide range of qualification here and it pays to find out whether a guy is a high ranking professional, a scientist, or just a playful kid before taking offence or running for a dictionary to decipher the reply. We all use different forms of dialogue depending on our experience and who we think we are replying to. We (or at least I) get it wrong too.

There's no reason to remove the heatsinks unless they prevent removing the Mosfets which, if your tests are correct, could be all that needs replacing. I haven't serviced this model (lucky for me) so I won't attempt to advise any further. You won't, however, gain anything by seeing the sensor devices underneath.

Note that if you replace the Mosfets, you then also do need to replace their thermal pads. They aren't difficult to buy as service items but distributors like Farnell and RS components, for some reason, only stock expensive US types. This UK Ebay supplier seems reasonable (Ebay ref.) 121109545678.

Replacing the Mosfets may not be the whole solution anyway and troubleshooting an amplifier this complicated is not going to be easy for a technician, let alone an inexperienced DIY. I wouldn't touch it - I'd take it to a qualified repairer with Arcam experience, if I expected a working amplifier at the end of the exercise.
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