Something is definitely wrong or you are doing something wrong with the measurements.

I did not request a measurement between pin 1 and 2 at D1201.

I need to know the AC voltage between pin 2 and 3 at D1201.

 

Sorry . Meant 2 and 3 the ac going into the rectifier, The voltage reading is 3.45 volts ac, unless there is something wrong with my meter. I am using a Fluke 73 Series meter.
Ground-pin 1= 6.96 volts dc
Ground pin 4= -2.65 vdc

 

These measur.ements were made with volume off and Q7512 and 14 still removed

 

Can you check your meter against a known voltage?
You need to check both DC and AC voltage ranges, for example, 9V or 12V for DC and 120VAC.

 

Ok I was able to verify 120 vac from the house supply. Reading 121 vac. Only had a 6 volt flashlight battery and 1.5 volt AA battery. They both checked out. 6.1 vdc for the flashlight battery and 1.61 for the AA battery.

I decided to see if the fuse would blow since we have removed the Q7512 and 14. Did not blow the fuse. Fan motor started. Smoke from connect board. Cut power real fast. Fuse did not blow.

 

We need to investigate what is going on in the power supply section.
Please post photos of the power supply and around D1201. We need to see how to disconnect the flow of power.

 

Disregard measurements from #61 up until now. Think I found the short. Looks like pins 4 and 6 were touching at the solder joint. Not really the solder joint, but the connector pins had not been trimmed well from the factory and were touching. After I pulled them apart, the bulb immediately dimmed. Here are the correct measurements now.

D1201- Between pins 2 and 3 75 vac
Ground to pin 1= -50.3 vdc
Ground to pin 4= 50.6 vdc

What next?

 

So happy I found the short I gave you the wrong reading for pins 2 and 3 on D1201. The correct reading is 75.2 vac.

 

Remeasured: B1+ voltage 4.14
B1- voltage -4.47.
Why did it change?

Have you changed the battery in your DMM lately? That will cause varying measurements

 

Disregard measurements from #61 up until now. Think I found the short. Looks like pins 4 and 6 were touching at the solder joint. Not really the solder joint, but the connector pins had not been trimmed well from the factory and were touching. After I pulled them apart, the bulb immediately dimmed. Here are the correct measurements now.

D1201- Between pins 2 and 3 75 vac
Ground to pin 1= -50.3 vdc
Ground to pin 4= 50.6 vdc

What next?

That is exciting news!
It makes a world of difference now. Now we can proceed one step at a time.

 

Now go back and take voltage measures at C, B, E on all four power transistor connections:
Q7511
Q7513
Q7512
Q7514

(Of course, resolder any jumpers you had undone. Keep the transistors off the board that were removed.)

 

Q7511 C=-43.8 vdc,
Q7513
Q7512
Q7514

After reconnecting jumpers to Bi+ and B1-. Short somewhere in system .Light back to almost as bright as before and a hum/buzz. Sounds to be 60 hz. Went back and rechecked my solder joint. Both ok. Now what? Frustrated now. Thought we were on the road to success. Sorry to be taking up so much of your time. About ready to toss this thing out. I would too, if it wasn't sort of a vintage speaker that sounded really good when it was working.

 

Hang in there. We're not ready to thrown in the towel yet!

Have a look at the +B1 and -B1 jumpers. There are two pairs, one pair runs horizontally, the other pair runs vertically. I assume that the ones you first lifted were the horizontal ones from CN7502 connector. With these back in place, lift the vertical -B1 and +B1 jumpers. This ought to remove power from the LEFT CHANNEL.

Then do the power on test again.

(Also we still have to investigate what was smoking in your recent power on test.)

 

Yes I removed the horizontal ones from the CN7502 connector. I will try the vertical ones this time.
The smoking went away when I separated the pin 4 and pin 6 short on the connect board.

Lifted the vertical B1+ and B1-. Unit back on. No smoke. Bulb filament very dim. What was the next step? I am all distraught about the failure. But I guess this what to expect when dealing with electronics.

I am n automotive engineer by trade(retired from Ford Motor Company) my expertise is in engine testing, Took the Bell and Howell course back in the late 70s as my introduction to electronics. It's been a long time. Now I am trying to brush up on electronics. Any recommendations as far as books or online courses?

So, what is the next step in find where the short is?

 

Have you changed the battery in your DMM lately? That will cause varying measurements

Battery checked out as good.

 

High winds and power outage at this end. Running on battery power now.

Test results suggest a problem in the left channel.
Leave things as they are and measure voltages at C, B, E at the four power transistors
Q7511
Q7513
Q7512
Q7514

(Yes, I am well aware that there is no power to the left channel.)

 

Q7511 C=0,0 vdc, B =0.0 vdc, E =0.0 vdc
Q7513 C=0,0 vdc, B =0.0 vdc, E =0.0 vdc
Q7512 C= -0.65 vdc; B=1.40 vdc; E= 50.1 vdc
Q7514 C= -0-.65 vdc; B= -50.4 vdc; E=-50.4 vdc

 

Have you purchased replacement transistors as yet?
You can try installing new Q7512 and Q7514.
Do not test with loudspeaker at this point in time.
Take voltage measurements first. You need have collectors at 0V before you are allowed to connect a loudspeaker.

 

I have NTE36 and NTE37 as replacements.
Complete #78 with jumpers still of B1+ and B1-?

 

Leave jumpers off. We assume there is a fault in the LEFT CHANNEL.
Make sure you make the correct transistor substitution. Mixing it up would be disastrous.