Next restoration: Yamaha PC2602M

[Cobra2]

Great job!
I have just restored an old, abused PC2602M myself. And have also been searching for bias-settings....
I looked thru a handfull of other Yamaha service-manuals, like
PC2002M = 11mV, P2700/P2350 = 15mV, P3500/P2500 = 15mV, MX-1000 = 10mV, M-85 = 15,5mV ....
So I tried some more - Idling at ~ 20mV, the fan would start a couple of times a day, and everything run quite hot to the feel.
(Near "class A"-hot).
Backing off to "Yamaha-typical" 15mV is still hot, but have not heard/seen fan-operation yet, on normal home-use.

 

[Cobra2]

For meters & LEDs, I cut a trace after the incoming ~11V-AC (front-pcb), and soldered a 1N4004 over, + added a 10uF cap after.
I used amber LEDs, soldered 3 in series+resistor, and used one lamp-wiring for each ch.
I noted that I could have dropped light-output some more, for perfection, as in a dim light, I can see slight light bleeding thru
from the LEDs.
I also swapped the red Power-LED for a green.

I swapped the caps on input-boards (C301,302,311,312) for new Muse bi-polars, but I think I will remove/short them,
as most other Yamaha-PRO-amps do not have any input-caps.
Also swapped the op-amps to LM4562.
"Refreshed"(swapped) all other electrolytics, exept main psu-caps. I also found new relays on fleabay.
And speaker-binding-posts that accept banana. (had to drill/enlarge the mounting-holes slightly).

 

[amr2]

Great job!
I have just restored an old, abused PC2602M myself.

Thank you! You have to post some pics...

About biasing. I'm using now the values posted by OMGCat!, about 4.5 mV on the emitter resistors, it runs soft warm, and the fan doesn't start on "normal" home use.

Anyway, I want a more silent fan. I used a Noctua NF-F12 PWM Industrial PPC. It has a little less airflow (88.3 CFM vs 75.33 CFM), but the noise is 15dB lower. A pic without the cover:



But I want a more silent operation, so I put a PWM speed controller with a NTC probe. The fan starts at 40% rpm, practically inaudible, and they are increased as the temperature rises.

 

[amr2]

Some final pics. It should be taken into account that this unit was abused, so I'm quite happy with the result.

 

[amr2]

The meters are a bit bright for indoor use. They are similar to those of the MX-1000, but the background is more transparent and lets more light pass.
I'm going to think how to dim the lamps, or replace them with leds.

 

[amr2]

Some pics before restore it

 

[Oldsansui441]

Has come up very well, nice job amr2.

 

[OMGCat!]

That looks nearly new, great restore. Did you have to redo the lettering on the front?
I see you're also missing the rear handle/cord winders on the back. I wonder if they were fragile and didn't take to getting banged around much.

I replaced my bulbs with the highest voltage, lowest mA 'grain of wheat' I could find and they came out quite dim and agreeable in low light (though I'd still rather no meters at all). I'm thinking about picking up an LED controller and using that when I go into it next.

 

[amr2]

Has come up very well, nice job amr2.

Thanks!

That looks nearly new, great restore. Did you have to redo the lettering on the front?

No I didn't. The faceplate had some scratches, but it was in good condition. I used a paint marker to repair these scratches.

I see you're also missing the rear handle/cord winders on the back. I wonder if they were fragile and didn't take to getting banged around much.

I don't know...the previous owner no longer had them. The rear fan filter was missing too.

I replaced my bulbs with the highest voltage, lowest mA 'grain of wheat' I could find and they came out quite dim and agreeable in low light (though I'd still rather no meters at all). I'm thinking about picking up an LED controller and using that when I go into it next.

That's an option. I would have to add a diode, a pair of resistors and perhaps a capacitor, like Cobra2 do. More resistance, less brightness.

 

[avionic]

Great job..

 

[amr2]

It's time to change the bulbs. The meters are too bright for me. I'm doing some test with leds that fits perfectly. I changed the color to red

You can see the difference here:

 

[avionic]

Like those red meters don't you.

 

[Mark B]

It's time to change the bulbs. The meters are too bright for me. I'm doing some test with leds that fits perfectly. I changed the color to red

You can see the difference here:

View attachment 880901

Much better!

 

[rottalpha]

I changed the color to red

Yep, much better!

Excellent work!

 

[amr2]

Just installed


and it's variable

 

[amr2]

 

[rottalpha]

View attachment 881554
View attachment 881676

very slick, I like it!

I am gonna try this on the MX-1k

 

[mech986]

I'm thinking about picking up an LED controller and using that when I go into it next.

Have wondered about using the tri-color (white, red, blue, maybe yellow too?) LED's that come in Christmas light strings now, plus they have a controller in a box (too big probably but heck, could take the innards out) so that you could change the color to your needs at will. Probably would need a nice green as well.

 

[TommyH76]

View attachment 881554
View attachment 881676

Hi!
Found this excellent thread .
New owner of two pc2602m.
One broken and one working.
Trying to fix the broken one.
Right now im fixing led on the meters.
The voltage on the old bulbs are 12v ac?
Do i need a diode bridge to get 12v dc before i use your schematics or is it drawn for ac?
Where did you hook the 12v from?
Best regards Tommy

 

[amr2]

Hello

The voltage on the old bulbs are 12v ac?

Yes

Do i need a diode bridge to get 12v dc before i use your schematics or is it drawn for ac?

There is a diode in the schematic. You can use AC voltage

Where did you hook the 12v from?

From the lamps supply (12vac)