Lol ok and thank u !

 

If it helps ..... I took measurements on other channel . Ch1 . R1-17 =.213v+
R1-18 = .137v-
This channel actually works and produces sound .. but voltages do not match either .....

Way closer than 500% off! And good idea to compare channels.
You can keep trying to measure, shotgun Q1 and Q2, or take a break.
I'm 64 years old and it's past my nap time.

 

Ok I'll try to study more on it

 

R17 has to carry the current coming through R13
R18 has to carry the current coming through R14.

Establish that this is the truth or find where the missing current went.
I promise, it is achievable. I have chased nano-amps into op-amps and found the error.
You can do this. Milliamps are a thousand times as large as some of the things I have traced out.

 

I found our culprit we never pulled R2-14 . It was infinity when I pulled and tested . I had no match to replace with so I used a 24 ohm resistor in its place . Should be in tolerance range . Correct me if I'm wrong . Now measurements are even and almost consistent .
R12 =17.32v -
R11= 17.42v +
R18=.189v-
R17=.189v+
Pin 7 of u2-1 =.194-
Q1 to q2 base to base = 1.8v

 

The problem was that with R2-14 "open" the (base ? ) of q2-2 wasn't getting it's 74.0v- which in turn stopped the current flow circuit from completing .and screwing all our measurements in process .lol how did we miss it

 

That's a collector, and it doesn't matter how you found it. You found it.
You have 2 methods: skill and luck.
I don't care whether you tracked it down with brilliance or just measured everything in sight. You won.

Now, check C15 and C16. If they are not shorted or open, you're ready to solder.

PS, you can put a 270 ohm resistor in parallel with the 24 ohm resistor to draw it down to 22 ohms...if it really is 24 ohms in the first place. A 24 ohm resistor could be 22 ohms and only be off perfect by 9% (within tolerance).

PSS, Notice how intent I was about matching voltages and currents, and see how important that is in a vertical stack like this. When you hit, "Bingo" you knew it instantly!

 

Lmao !!! Only possible with your help

 

C15 and c16 all good

 

Would it be safe for the circuit if I replaced power transistors with say a 75 watt instead of the 150watt it calls for ?? Just to test the circuit ?? Because my new replacements won't arrive till Jan .

 

Well, yeah, but you know the penalty for failure...Death!

Keep it to just one speaker per channel and don't go above a conversational level of loudness or you're going to smell smoke. Be sure the 75W transistors are good for the voltage applied. Voltage failure also causes them to smoke.

 

Ok I'll think about that can of worms tomorrow lol . Sleep on it and all that ....

 

I recommend you do NOT put more wear on the circuit board by soldering and re-soldering the same copper spots. They do eventually get damaged.

Now. Clean the potentiometers and re-solder the circuit boards. You will be too impatient to do that after the parts arrive.

What are you waiting for? Do it now!

 

ok so i got the new power transistors in from china today .... going try install and fire this puppy up

 

ok so i installed chips double and tripple checked everything and when i powered up it worked fine for three seconds then r2-13 blew out . so now what

 

ok so i replaced r2-13 and replaced q2-7 and q2-8 with 100watt power transistors and it worked about 10 secs then blew out r2-23 . i really need some help with this guys . what am i missing ??

 

ok so these are the replacements i used for q2-7 and q2-8

 

Start over, but this time you have another option besides broken parts...human error. If Q7 has a different pinout than the original transistor, that would explain everything. So would a solder blob from the base to the emitter connections of Q7.

 

no i checked all solder joints very carefully 3x . and pretty sure pinout is same
these are chips called for in schem . compare to mine

 

oh btw 2sc3281 blowed showed no good after r2-13 blew out . and im not ordering from china again lol .