The Yamaha P-2200 restoration begins

The fun part about giving this guy a first look-through was that it did actually turn on, and it did actually play on both channels … barely. The right channel was heavily distorted and  about half of the time when the power switch was flicked, it’d only flicker and buzz for a while before setting the breaker off.

The turn-on issue was caused by a severely worn-down power switch. The contact surfaces had literally vaporised and disappeared from switching that 1,3 kVA transformer for thirty years. There’s no remedy able to get that into shape for switching big loads again. At least not without giving it a helping hand.

A helping hand in the form of a 230 V relay. I even went the extra step and added a capacitor across the coil in order to make the life of the switch easier.

Testing the relay circuit (animated GIF – clickit!)

While I wouldn’t trust a transformer to this, it should switch the relay for many years to come.

The hot-glued, PVC-taped relay board is simply placed loosely behind the front panel.

It workes very well, however there should be two relays used if you’re to be picky; the original switch is configured to turn the two primary windings on at slightly different times. This is in order to reduce the start-up current somewhat.

(I was later informed that switches such as these, commonly found in AT computer chassis’ would probably work as replacements.)

With the power switch issue out of the way, let’s move on to some intensive maintenance of the actual electronics. Starting with a re-cap.

Two 470 µF capacitors for the size of a thirty-year-old 220 µF

Old and nasty.

Worth noting is that C101 and C201 (100 µF/10 V) were actually completely dried-out; they didn’t even register on the meter. It’s odd that the amplifier worked at all without them, as they seem to be in the signal path.

It’s hard to imagine that these capacitors are both more reliable and more powerful than the old ones.

While new caps are always fresh and nice, it didn’t remedy the right-channel bias issue. The cause for that was two-fold and somewhat unexpected. For starters, the bias adjustment potentiometer looked like this on the inside:

The less obvious issue, however, was that a small (0,47 µF) tantalum capacitor, C113, was shorted. It’s connected across the base and collector of one of the transistors in the bias circuit, as well as across the bias adjustment potentiometer. Short-circuiting C113 is equivalent to turning the bias down to zero.

The affected channel had been serviced before and a lot has been replaced. I’d wager that C113 failed at that time and that the service technician didn’t bother actually listening to the amplifier before giving it back to the customer. Nevertheless, replacing C113 (with a 2,2 µF electrolytic; C213 was also replaced to avoid any channel imbalance) and VR101 (the bias pot) remedied the problem. The channel still has a slight DC offset of 20 mV or so, but I’ll live with that for the moment; there’s still a few transistors that should be renewed.

The same service technician also installed MJ15015 and MJ15016 transistors for the output of the channel – transistors with a maximum VCEO of 120 V! The power supply rails in the P-2200 add up to 160 V; 120 V transistors have no place in such an amplifier. It may work, but any safety margins intended by the designer are lost. If the output terminals are shorted or over-loaded, these transistors will be up in smoke before you can even think “blown outputs”! The proper MJ series transistors to use would be MJ15022 and MJ15023.

For shame.

Anyhow, with that bitter-sweet story out of the way, only the cleaning-up remains. I’ll spare you the narration, enjoy!

And that’s it! The only things remaining to do is to give the incompetently serviced channel another overview in the future, replacing driver transistors and of course outputs. One of the thermal indication thermostats has also failed, so I might replace that some time in the future. That’s a minor issue though.

Thank you for visiting, I hope you enjoyed reading about this project as much as I enjoy listening to it!

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24 thoughts on “The Yamaha P-2200 restoration begins

    • Jamen, se på tusan! Jag slarvade visst med efterforskningen! Medan jag nog låter min fullösning sitta kvar, så ska jag ta och lägga en rättelse i inlägget.

      Tack för kommentaren!

    • Jag mätte faktiskt båda två i dag (dock endast med resistiv last). De presterar i grova tag identiskt (fast det ju då finns 120 W per kanal extra att ta av i Yamahan). Yamahan har även en mycket högre (350 vs. 50) dämpningsfaktor till sin fördel. Någon hörbar skillnad tror jag dock inte det rör sig om, men det skulle vara kul att se hur de står sig mot varann i ett kubtest.

  1. Dear Sir I am rebuilding my Yamaha P220 amp. The left VU meter is faulty, suddenly goes haywire
    for no reason.. Any suggestions? Does not affect the sound..
    Regards
    John Baum

    • There’s not much I can say without looking at the unit. I’d begin simply tracing the signal with an oscilloscope, starting at the meter and working backwards, until a fault is found. If the problem can be triggered by banging the unit with the palm of your hand, it’s likely to be a bad solder joint or connector.

      Good luck!

  2. You didn’t replace the PSU caps? I have a couple of these amps and thinking about recapping them, as they are all original, would you leave the big psu caps alone?

    • No, I didn’t, because they measured fine, and failures in huge capacitors like that is extremely rare. If you have the funds, they should be replaced.

  3. Nice work on the restoration.

    What replacement trimpot do you recommend for bias adjustment on this amp?

    Also, were you ever able to decrease the DC offset? Mine has 23mV and 43mV. There is no way to adjust that I can tell.

    • I just used a run-of-the-mill pot that I purchased at a local TV repair place. I don’t know any specifics about it.

      I don’t think I ever did anything about the DC offset. I wouldn’t worry about anything under 100 mV in an amplifier like this.

      • Thanks for the reply.

        Good to know that the offset is ok.

        I was going to replace the pots on mine but there are several different 1kohm pots available. Would a Bourns 1kohm with a 1/2 watt power rating be sufficient?

    • I’m afraid not, I basically just filled out a Mouser order for the few parts I missed as I took it apart. Most of it was replaced with standard values.

  4. hi i am looking for the light bulbs and if possible the board for the bulbs and also the 2 huge capacitors

  5. Can anybody tell me where to find the light bulbs for the meters with or without the board

    • For bulbs, go here: http://www.dgwojo.com/

      For the caps, either Mouser or Digikey should have those.

      Although, is there really something wrong with the large caps on your amp? I changed all the caps on mine except for the large caps. They measured fine, no leaks, and they are expensive for new ones. About $35 each, IIRC. The amp sounds fine with the old large caps.

  6. thanks you so much know i am getting so help from digikey they told me i need to know the resistant on the thermal lead switch this amp is really missing parts so i am doing step by step. i got got the bulbs &the 2caps

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