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Old 3rd March 2006, 09:38 AM   #1
Luke is offline Luke  New Zealand
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Default pm78 schematic or service manual

Hi anyone have this?
Can only find one place on google that sells cds for 25 dollars.
This thing has a blown channel and I havent recieved it yet. It also needs a new transformer, what are the rails on it?
It uses HDAMS so I am thinking of replacing drivers and outputs on the blown channel, but a manual would help for some tweaking:-)
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Old 4th March 2006, 04:14 AM   #2
Luke is offline Luke  New Zealand
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anyone??
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Old 5th March 2006, 12:06 AM   #3
anatech is offline anatech  Canada
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Hi Luke,
Sorry I can't help with the schematic, but what makes you think the power transformer is bad?

Sometimes you can replace the thermal fuse if you can get to it.

-Chris
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Old 5th March 2006, 12:55 AM   #4
Luke is offline Luke  New Zealand
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Quote:
Sorry I can't help with the schematic, but what makes you think the power transformer is bad?

Hi Chris,

Well the story goes, its belongs to a guy who was working abroad and got the voltage wrong, zapped one channel.
This amp is 110V so I would change it 230V even if it were ok.
What I dont know is if the transistors are hard to get and if I should just change them to the latest Toshibas on both channels anyway.
one of my aims is to tweak the amp to see what performance I can get out of a low price amp. Currently I have aleph 2s, Krell ksa50, JLH couple of gainclones, so I am curious what I can get out of a midfi tweaked amp.

seeya arthur
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Old 5th March 2006, 01:27 AM   #5
anatech is offline anatech  Canada
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Hi Arthur,
Sounds like a plan. With any luck the guy just popped the fuse. When transformers overheat they generally make a sickly sweet / burnt smell.

So you're making an amp for your computer speakers?

-Chris
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Old 5th March 2006, 07:07 AM   #6
Luke is offline Luke  New Zealand
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Quote:
So you're making an amp for your computer speakers?
lets just say its a reality check Maybe it will give me the motivation to finish the Aleph-X.

seeya arthur
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Old 6th March 2006, 11:32 AM   #7
sangram is offline sangram  India
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I did that too! On my PM665. I'll see if I havea copy of the manual but I got mine from a very kind member on this site, maybe if you did a search...

I remember we had to replace the driver transistor. The main power supply caps would like to be changed after this sort of a thing, they were OK then but show accelerated aging...

The transformers should mostly be OK, they could survive the x2 voltage. I changed out the transformer to custom units. The manual specified 53 volt rails, so I used 38 volt transformers...
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Old 7th March 2006, 09:50 AM   #8
bekim is offline bekim  Albania
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Hi,

I don't have schema for this amp, but I serviced one years ago adn, is same like pm68 inside exept some wiring and resistors which turns to class A.
Regarding transformator, I think is 45volts per rail.
Output trannies are toshiba 2SA1941/2SC5198 and, you have to be careful with those small metal boxes called hdam. Might happen sometimes any transistor to misbehave, so you have to check one by one.

I agree, you better need schematics in order to fix it, it took my 1 month and half until i fix it...

bekim
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Old 7th March 2006, 08:09 PM   #9
Luke is offline Luke  New Zealand
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Hi Sangram and Bekim,

thanks or your input. I would have thought that the outputs and maybe drivers have failed. I hope not the hdam
Bekin, is the transformer 45V or the rail voltage 45V?
Maybe PM68 schematic is readily available on web. Thanks for the tip


regards Arthur
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Old 13th March 2006, 02:34 PM   #10
bekim is offline bekim  Albania
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45 volts is per rail, to be sure now, hmmm ... frankly, I forgot but, usualy this models have 45v per rail - pm68, 78, pm7000 & 8200..

be careful with zeners in preamp pcb..

bekim
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