eccessive feedback and slight loss of output

[sadgod]

hey guys,
A friend of a friend brought me an Ibanez toneblaster 50R. He says it has a "weird echo and doesn't have as much power". I guess it only does this on occasion. I took it home with me and played through it. I had a heck of a time hearing anything wrong with it. Its a SS amp and it sounded like one. Like many SS amps it has a lot of distortion on the hot channel. But when the distortion decays it makes a crackly sound, it has ALOT of feedback. I don't know what he means by the echo noise? It has a crappy spring reverb but there isn't anything wrong with it. I considered the fact that he could have something in his band environment that could have caused the echo noise. I used to have a pv bandit 112 transtube and as far as volume goes the pv was much louder (sounded alot better too).
I started troubleshooting by plugging it into my Marshall 4x12 cab. Sure it was a little louder and fuller but not as loud as I think it should be. I opened it up and everything looked fine ( I hate when things aren't obvious). I let it power up for a while nothing was too hot. The first thing that comes to mind when I think of some of the symptoms are xsistors and it looks like fets are used also. I am more of a tube guy but I don't like limiting myself. It uses 4558 ics and i tested pins 2 and 7 on all of them and they came through fine. no resistors out of tolerance. Diodes were fine. 1uf Jun Fu electrolytics throughout. they look pretty cheap (not a straight looking radial shape). I'm not up to snuff when it comes to testing fets and power transistors. On my stuff I use the shotgun approach on transistors and electrolytics and it has done well for me. but I should trouble shoot them if I'm not the one paying for it. Uses Mospec tip42c & 41c, tip32c &31c, and Toshiba A1941 & C1598. Any suggestions would be appreciated.

[sadgod]

I think I know what hes talking about with the echo. there does seem to be a lower ghost note in there after a played hard and long on the low e. And the grounding doesn't seem right in to the cable and through the input jack. coupling issue?

[Enzo]

So see if the power supplies are getting soft. AS a rule, transistors don't get weak like tubes. They are more like 12AX7s - they work until they fail.

Transistors short, open, get real leaky (an almost short, if you like), get noisy. If the amp works, it likely is not the transistors. I'd be looking for a coupler, a noisy op amp.

That is pins 1 and 7, by the way. Pin 2 is an input. often cannot measure signal at the input pins of op amps. Just be comfident that if it is at the output pin, it must be at the input pin too, regardless.

[sadgod]

What is acceptable amount of voltage to pass through those pins. 2 out of the seven 4558s had around 4mv

[sadgod]

wish I could find a schem

[sadgod]

it does it when the guitar is used and sounds fine when its not plugged in. Guitar sounds fine with my other amps. it seems to act like there is a grounding issue . I recapped the power supply and output and lead channel. alot of lytics in this amp. I have all 7 of the 4558 opamps this thing use on hand. I really dont want to replace them if I dont have to unless theres a better way of doing it. it will take forever unless u guys know some tricks. it also makes a nasty feedback noise when i slide my finger on the g string, (if u now what i mean)