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Old 11th February 2006, 09:14 AM   #1
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Default Yamaha pc2002m

Hello,

I am busy with bringing the right channel back to life from an old Yamaha pc2002m. It's work in progress and I want to stick to the original components and luckily I found through my job a collegeau from Japan who will get the original 2sc2238b and it's counterpart 2sc968b.
I have the manual as well, the schematics look quite decent, as I've seen this topology before in other amps (also a bit similar to the lfa 150 elektor)
Also built quality is impressive, I guess one of the reasons why 70ties audio is so popular (got a Marantz 2238 on the shelf and monster Mitsubishi..no plastics)
I will be very curious how it sounds, but anyone interested in the manual, let me know.
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Old 15th February 2006, 12:07 AM   #2
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Haai HaaiFaai,

I am on the lookout for a PC2002M at the moment.

I've used many of these amps before, and I agree that they are quality bits of gear. I think they are one of the best sounding amps Yamaha have ever made and super reliable. You will like what you hear!

I would appreciate it if you could send a copy of the service manual or just schematic in case the need arises one day.
I'm happy to pay for postage etc if it's a paper copy.

Cheers,
Ralph
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Old 19th February 2006, 05:02 PM   #3
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Hello Ralphs99

It's a pdf file, so I can send it to your email address. Currently I've optained the drivers, 2sc2238b and 2sa968b, although only one was broken, will just replace them both. This amp is quite easy serviceable too.
I noticed that this topology was also used in a Stage Accompany amplifier which used to be a state of the art beast in the 80ties.
The previous owner only used one channel and didn't want to invest I guess in repairing it (those output transistors are here in europe between 15-20 euro's each with 8 of them missing) so fo testing I will first use the often used combo mj15025 and mj15025. Will use some big resistors in the power lines before going full monty.
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Old 19th February 2006, 08:59 PM   #4
anatech is offline anatech  Canada
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Hi HaaiFaai,
I'd love a PDF please. Send to: bhomester at gmail dot com.

I used to service these. They sounded very good actually. There was a solder connection issue with the sockets for transistors mounted on the heatsink I think. Cracked joints, resolder them even if they look okay.

As I recall they were very clean sounding, very little background noise.

-Chris
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Old 19th February 2006, 09:24 PM   #5
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We've got our own little fan club going on here!

Thanks Haai Faai.
I'm sending you a message with my email address.

Good luck with your repair.
That's smart thinking about putting resistors in series with the mains lead. A tech I worked with once used a couple of light globes to achieve the same effect. Cheap, simple and self protecting.

Cheers,
Ralph.
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Old 20th February 2006, 05:58 AM   #6
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The resistors are on the plus and minus lines, so in case of erratic behaviour due to wrong voltage/currents of driver/output transistors, the resistors will go up in smoke rather then the transistors themselves ;-)
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Old 25th February 2006, 04:31 PM   #7
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The amplifier is doing a test run, all parts original except for one 2sa999 which was pin compatible with a bc640 (current limiter circuit). Idle current stays stable and it's running without the test resistors and with the mj15023 and mj15024...the original output transistors will be placed after operation is proven ok.
First impression is a very clean sounding amp..
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Old 25th February 2006, 04:49 PM   #8
anatech is offline anatech  Canada
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Quote:
First impression is a very clean sounding amp..
Yup, cleaner than you would expect from a PA amp.

Shouldn't you be using MJ15022 and MJ15023, or MJ15024 and MJ15025 as complimentary pairs for your outputs?

-Chris
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Old 26th February 2006, 08:30 AM   #9
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Yes I use a complimentary pair, although one pair is rated 250 Volts max, while the other is 200 Volts. (Those I had laying around) So the mj15023 and mj 15024..if this runs fine I will replace them with the 2sc2608 and the 2sa1117 ( 8 in total)

The 2sc2608 and 2sa1117 are both rated for 200 volts, so I have a safe margin when using those Motorola workhorses ;-)

Btw, it's a tip to use the mj series when you do a first test run, as those are rugged and cheaper then the original ones ;-)
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Old 26th February 2006, 03:43 PM   #10
anatech is offline anatech  Canada
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Hi HaaiFaai,
Really, you could just leave the Motorola parts in. Why spend the money on expensive parts when you could just stay with the good Motorola parts? If you really wanted to, you could use the newer MJ21193 and MJ21194 pairs.

-Chris
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