PC5002M

[Overundr1]

Egads, what a monster.
Anyways, about to open one up and chase down a start up fault.
Story from owner --- Unit would take anywheres from 20 seconds to 20 minutes to come out of protection on right channel then play fine until shut off again (remember this is a true dual mono block amp with independent left and right channels. Unit was checked out at another shop and no issues where found and returned. Shortly afterwards unit failed to come out of protection at all on the same channel.
Before I get out the forklift to lift this thing up on the bench I had a look through the schematics. The input transistors are a pair of monolithic sip matched pnp (upa75) and npn (upa74) 7 pin arrays which of course or really not available anymore. Schematics also indicate the max voltage on the collectors is less than +/-16v and I cannot find a gain spec however my initial thinking to to gain match a pair of ksa992 for pnp and ksc1845 for npn. Will check voltages of course before firing up the soldering equipment however was hoping one of our esteemed Yamaha techs has been down this road before as there is very little on the web about this amplifier.
-Lee

 

[rottalpha]

Hi Lee, a monster indeed. On my radar for a long time, but I need to buy that forklift first.

It should not be too hard to match those KSA/KSC.
Good luck!

 

[avionic]

Before I get out the forklift to lift this thing up on the bench

Thats and under statement. 61 Kg

 

[Overundr1]

I just finished this 125 pounder earlier today, poor back taking a beating lol.

 

[rottalpha]

I just finished this 125 pounder earlier today, poor back taking a beating lol.

View attachment 1105512

Lightweight

 

[clinic-audio]

Hello
your meters are not adjusted and the red LED (power ON ) is off

 

[Overundr1]

Can't order the 058-040 special secret double probation McIntosh bulb from Audio Classics till Monday and the meters were showing live source music not sine wave test tones sheeesh
Now back to the topic at hand
-Lee

 

[Overundr1]

Anyways, pulled the buffer circuit board out this morning and spent the better part of three hours checking all the transistors and diodes and inspecting for cold solder joints etc. Put the board back in and re-seated all the inter connect cables and unit comes out of protection without issue. Next is awaiting rca to xlr cables from owner to see if having them hooked up was causing the issue

 

[Vint Age]

What a monster that amp is. Love to have one... Good luck while a day dream...LOL

Yes indeed and ditto that!

 

[Overundr1]

Worth noting that the schematics do not begin to indicate the sheer density and complexity of parts in this amplifier, and until you get the covers off there is no way to realize the level of Quality Components Yamaha chose, everything is top shelf. Of course once I am sure it is running correctly there is no way I could possibly test to full output since I do not have 1200 watts worth of dummy loads lying around.

 

[rottalpha]

Worth noting that the schematics do not begin to indicate the sheer density and complexity of parts in this amplifier, and until you get the covers off there is no way to realize the level of Quality Components Yamaha chose, everything is top shelf. Of course once I am sure it is running correctly there is no way I could possibly test to full output since I do not have 1200 watts worth of dummy loads lying around.

I do, send it over.

 

[Sound Dragon]

Thos amp is on my bucket list to own.

 

[Mark B]

The PC5002M is a great amp. Kinda heavy though.

 

[cdfac]

Anyways, pulled the buffer circuit board out this morning and spent the better part of three hours checking all the transistors and diodes and inspecting for cold solder joints etc. Put the board back in and re-seated all the inter connect cables and unit comes out of protection without issue. Next is awaiting rca to xlr cables from owner to see if having them hooked up was causing the issue

I dunno, I'd be skeptical that it's fixed. But if it is, you and the owner are the luckiest SOB's around! That is easily in my top 3 best amps ever owned.

 

[restorer-john]

...there is no way I could possibly test to full output since I do not have 1200 watts worth of dummy loads lying around...

Go buy some cheap electric jugs and fill them with water. They are pretty much purely resistive and it seems most of them over there (US) are around 1.5KW so that makes them 12.5ohms. A couple of 2000w kettles in parallel would give you very close to 8ohms.

After you've done with testing (and boiling the water)- you can have a cup of tea as a bonus.

One of our Kiwi AKers uses 4 electric jugs to soak test amps.

 

[Overundr1]

Yeah, would be nice if it came down to tarnished or unseated connections. Will know more once I can run test signals through it and start verifying voltages. If I have to get into the driver boards (which are under the buffer board) things might get a bit hairy. Also worth a mention that the component density is really high and Yamaha mounted everything really tight to the boards making measurements a real challenge. Cool idea on the kettle's.

 

[Beobloke]

I'm jealous - yours is a lot cleaner inside than mine!

 

[jblnut]

That's quite an AMP! Really enjoying your refurb thread here.

It's one of two white whales that I tracked but never got into the boat. The other being the Citation XX.


jblnut