Yamaha SPX90

[lowell]

I think this may be a good sub for the 2sc2555 since I can't find any of those.

ON SEMICONDUCTOR|MJE5742G|Darlington Bipolar Transistor | Newark.com

Only issue I see is that Rise time is .5 instead of 2sc2555's 1.

[Enzo]

No. other issues are that the MJE is a darlington with a gain of 400, while the C2555 is not and has a gain of 10. The MJE is in a TO220, while the 2555 is in a TO3P. Otherwise, reasonably close.


MCM is currently subbing it with a 2SC3306 for $2.99

B&D Enterprises is currently subbing them with 2SC3042 at $4.28

The thing is 20 years old or more, the transistor is obsolete. I have one of those power supplies here, I looked, and even from way back them, it has an ECG something in it. Of course it doesn't work either. DOn;t know if the transistor is involved. Maybe someday I'll fix it.

[zero cool]

I think this may be a good sub for the 2sc2555 since I can't find any of those.

try a 2SC3042 this is listed as the replacement/

B&D Enterprises: Part #2SC3042

[lowell]

ok thanks guys.

[g1]

I hate to bring this up but I do remember going through one of these and replacing many parts, much labour, only to find one of the transformer windings was shorted. The transformer of course was no longer available. At the time we had no inductance meter and assumed that a low resistance reading on the winding meant it was ok.

[lowell]

g-spot,
yeah i've been a bit worried bout that too, but what the hell right? I did however plug it into my bulb limiter w/ Q1 removed and the bulb does not glow, so that's a good sign.

[lowell]

Replaced Q1 and the thing is banging. Thanks guys for all the help!

[Dirk_Hendrik]

OK, here's the secret to servicing a dead SPX90:

First of all, the cause: Yamaha used an adhesive to lock down components on the power supply PCB. The adhesive carbonizes after many years and becomes conductive, creating phantom resistors in the circuit where they don't belong. What winds up happening is that filter caps dry out, diodes tend to overheat and open up, and even some component leads corrode.

The first thing you must do is scrape away all of the carbonized brown muck (it was originally off-white). Get under the components with a dental pick and get it ALL out. Then clean the board with flux remover and an acid brush. After you've done that, look at the filter caps on that side of the circuit. If any are swollen, they need to be replaced with good, high-frequency 105°C caps. If all look good however, power up the unit. After scraping the glue off, there is decent chance it might actually work. If not, replace the caps and all of the high-efficiency rectifiers. That is usually the problem.

Bumping an old corpse.
Thanks jrfrond,
I would have found my power supply error eventually but this post saved me a few hours! Highly appreciated!

[kdawg]

Also bumping this ancient thread...

I have an SPX90 that functions normally until left on for several hours. The 18v rails drop to about 5v and the main display goes out, all VU meter segments light up. I recapped the main board and scrapped off the gunk, no changes. If I unplug the CN3 going to the main board, 18v rails go back up and the main display turns back on.

I see 7815 and 7915 regulators by the connector, and a few caps - could those be going bad after heating up? I don't have a schematic of the main board so not sure what to check.

Any ideas? Thanks!

-kdawg

[Enzo]

That is what freeze spray is for. If you think a regulator is failing under heat, then when the voltage drops hit the regulator with freezit and see if the voltage pops back up.