Tell me how it's a calculated guess when your troubleshooting an amp based on other threads.   You for get some of the people here have been in the business for a while and a cost benefit thing to them is to replace only the bad part.  If the test are not reliable may it is the person performing the tests.  These guys will not steer you wrong when giving you a procedure.

If you want the best chance at success with the least effort maybe you should take the amp to a qualified tech rather than bucking good advice.

my 2cents and then some

nosaj

Replace L1 with a 4.7 ohm, tacked 2 diodes back in, put Q10(?) back in circuit .
And we're rocking and rolling again. Loud like it should be.  Another piece of usuable equipment rescued from the trash.

Thanks so much Enzo

nosaj

Well I'm glad i did pics and asked then.

Thanks,
nosaj

Here they are

And another 2 pictures of what I believe are the heat sensing diode and where it is hooked up(not a molex connector but one lead to a fuse and the other to the on/off switch)  This is how I found that connection it was soldered So I had left it there. 

Let me know what you think. I'll be replacing L1 in the morning and hooking it back up to see where we're at and if there's any updates.

Thanks so much
,
nosaj

Enzo,
Maybe this helps you wrap your head around this.  For the most part eavey Molex pins are keyed from what I've seen so I have been plugging the speakers in to the connector by c26 instead of by L2.  I noticed this last night by pouring over the schematic. I've still got L1 and a resistor to replace for sure though and maybe other parts?

Thanks,
nosaj

Any suggestions on what else to check when i replace the 2 burned components?

Thanks,
nosaj

Ok  I lifted cr10 and cr15 and removed Q10 and tacked a cap on C8.

No change in volume output.  So using sig gen with a cap on the end and started probing Q9 base an signal is still low. So I probed Q2 emitter which caused L1 and R61 to burn.

Jason

c8  50/50v has 24vdc on oneside and 1.09vdc on the other
c21 2uf/35v has -13 on one side and -3.88 on the other
c11 2uf/35v has 4.5vdc and 14.65 vdc one the other

I'm gonna have to see what I have on hand tomorrow. Would a 4.7 uf work in c21 and c11. i may have a 47uf/250 to test with.
Will have to pull the requested parts tomorrow.

Injecting signal at q9 collector was louder than injecting at the molex pin.

Nosaj

i understand on a tube amp where I can inject signal but on a Solid state amp where would one inject signal at?

Thanks,
nosaj

Low volume is what I'm getting not even as loud as a portable radio.  I'll verify Q9 shortly.

Thanks,
Jason

on the schematic  the top row of transistors  E -51.22 and B -51.22  C -.07
bottom row E  -.09          B    -.09            C    52

Q9 E -51  C  -.16  B -50

Signal coming  out of U1 pin 14  is larger than the input it is amplifying there.

This is just a guess since i don't quite understand whats happening 
Q9's B should be .96 not -51
Q2  E -.07  B .37  C 51.

Thanks nosaj

Quote from: Enzo on July 15, 2016, 11:32:06 PM
The patch was ONLY going to tell us if one of the jacks had an issue.  If a circuit has a problem, patching won;t cure it.

But did we put signal into the PA IN jack?  If that is weak, then the power amp is faulty and we can certainly fix it.

Power SUPPLY?  If you have both 50v rails and all the 15v rails, then power supply is OK. 

The ICs are in sockets, right?  Assuming the power amp is bad.  Isolate it.  Pull that five wire cord from the corner of the 400 board to the master board up front.  Just operate the power amp alone.  You can use clip wires to input signal to it right on the now bare connector pins.

There is the small IC, the 87478.  Pull it.  Does the sound recover?  That IC is the compressor/limiter.  Try a different TL074.  If you don;t have any, steal one from the front panel boards for test purpose.   And there is also a single 4558 on the 400 board, it too is a limiter, pull it.

Inserting signal at the 5 wire plug connector on the 400b/g board signal is still low.  Pulling the 87478 no change in vol, tried a new tl074 no change  and u3 for the 4558 looks like it was never installed.
Re verified power rails  50v and 15v.

One thing I did notice  (by the 400bg silk screen logo)the white/blue/red cable connector has -51v on two wires  Whereas the other white/blue/red cable only had +50v on one of the wires..
Tomorrow I can be more specific on the wire colors with the voltage  it's pouring here and shed is separated from house which is where the internet is.

Thanks,
nosaj

Will do. It will be Sunday evening before I get back into town before I cando any of it.

nosaj

scratch all that.   meter was on ohms instead of voltage.
8ohm load .1 to .01  you can hear what sounds like a heartbeat real low  I'm guess something is motorboating.
no load  is .03vdc.
no combination of patch cable increase volume.

So I would venture to say it is in the power supply.

Dim bulb is no longer being used.
Also the compressor light is constantly on.
Thanks,
Nosaj