Yamaha P2250 Transistor Replacement

[JB Lonewolf]

Hi,

I got a guy who wants me to fix his 80's Yamaha P2250 power amp. The thing went into safety mode because the trans on one side are just starting to trickle DC. The orig parts are 2SA1303 and 2SC3284 which seem to unavailable except Chinese fakes, been there already. Is there any reason 2SA1943/ 2SC5200 which are in production and fairly inexpensive could not be substituted? They have a higher voltage rating, main difference I see is frequency, being more of a tube amp guy I don't know if that makes a big difference.

Thank you in advance,
JB

[The Dude]

If an output shorted, it wouldn't "trickle DC". The amp would likely blow a fuse. Generally speaking, although there are rare exceptions, those transistors either work or they short and don't. Did you check them? From your description of the problem I have doubts they even need replacing.

[JB Lonewolf]

Thanks for your response. Just to clarify, this is a stereo amp. Outputs on the one side/channel were not shorted, rather were starting to leak, about a volt or so, enough to trigger the safety circuit. The other channel works/ no safety shutdown when the leaky channel is disconnected. I need to replace the leaky trans which are apparently extinct and am asking about available replacements.

Once again thank you for your reply,
JB

[glebert]

Do you have a schematic? Please post if you do.

Echoing what The Dude said, I would be looking more at the voltages upstream from the ouput transistors that might be turning on the output devices more than they should be at idle.. I've had problems with leaky capacitors on the diff amp section of Yamaha guitar amps of this era causing some inbalance issues. I've also seen other brands of amps that had leaky caps that charged up the protection circuit even though the output devices weren't conducting. The schematic will help look for stuff like that.

[JB Lonewolf]

Thanks for your response. I've already removed and tossed the orig trans as a couple of PNP's read low ohm wise, this amp has sockets and it's easy to replace power trans. Here is a service manual, it's a 2250:

[JB Lonewolf]

And as far as trans replacements go, the orig trans were 2sa1303 and 2sc3284. Would 2sa1943 and 2sc5200 be a suitable replacement? These are the specs for the PNP's:

Thank you again,
JB

[g1]

There are HFE classifications for the original (O,P,Y) and for the sub (R,O). It would be best to try to use the version closest to what the originals are.
Other than that, they should be fine.