A/D/S power plate 80 and 100

[Rabbit 16v]

All pins have the save voltages as measured at the board for the modules using the filter caps as reference ground.

 

[Perry Babin]

Was the section of the diagram with Q608-611 the same in your amp?

 

[Rabbit 16v]

Unfortunately, no.

 

[Perry Babin]

Is the circuit the same but the designations different?

 

[Rabbit 16v]

It is not. A couple pages back I posted a diagram of three transistors that are on this board and their configuration. I have since removed all three and bench tested them and they all test fine. The schematic I drew and posted is as close to the diagram as it gets.

 

[Perry Babin]

If you're referring to post 175, that's insufficient. It shows no connections to anything, no resistors/resistor values, essentially nothing.

 

[Rabbit 16v]

Agreed that wasnt probably the most useful schematic. I mostly drew it to show the arrangement of the transistors in the circuit. I will hand draw one this week to cover that area. Not sure if it matters, but I have removed and bench tested every transistor on the audio board and they all test ok. Thanks again for your patience with me.

 

[Rabbit 16v]

Ok, this took a bit. Not sure how far out in which direction I should go here. Is this helpful? the big arrow is ground for both rails (the one with the filter caps on it we have been using as reference when checking square wave)

q1 (q608) a733 PNP
q2 (q602) c945 NPN
q3 (q603) c945 NPN
r1 11k
r2 1.2k
r3 100k
c1 10v 100mf
r4 27k
r5 27k
st1 left speaker output pos
st2 right speaker output pos

 

[Perry Babin]

Why didn't you use the right designations on the diagram?

mF should be uF unless it's a huge capacitor.

That circuit appears to be the DC offset protection. You could remove those transistors and the amp would work normally. Try reconnecting the SCR gate and removing these one at a time, starting with Q1 to see if the amp shuts down.

 

[Rabbit 16v]

I didnt know how to make the special character for "micro", so i thought "m" would suffice. sorry, Im glad you understood it though.

I reconnected the gate leg of the SCR and removed Q1. Problem is no longer present and it maintains square wave signal.

 

[Perry Babin]

Is the relay engaging?

 

[Rabbit 16v]

the only relay for the amp is the one for 2 speaker vs 4 speaker. When powered up, yes it will switch when I push the button. Rail voltage goes from 33vac to 26vac when I depress the button. All tests have been performed with button out placing it in two speaker mode.
if that is of any import.

 

[Perry Babin]

OK. Do you read any DC voltage across the two terminals for any channel?

Try with the switch in both positions.

 

[Rabbit 16v]

If meter probes are polarity matched to the speaker outputs, both channels have +2.1vdc. Switch position makes no change in readings.

 

[Perry Babin]

Short each pair of terminals with a wire. Power the amp up. Is there any significant current draw (more than what it previously drew)?

 

[Rabbit 16v]

Well, I dont have my 87 meter here so I cant check current. I did check voltage and it is the same at 33.4vac with terminals shorted. Did this with both channels and nothing that indicates to me any big jump in current draw. Then again, I dont have an ammeter on it.

 

[Perry Babin]

OK. Reinstall Q1 (leave the jumpers). Do you lose positive rail?

 

[Rabbit 16v]

Q1 reinstalled, jumpers left in place. No rail voltage on either side.

Incidentally, prior to reinstalling the gate leg on the SCR, I did verify rail voltage. Then installed the gate leg and verified no rail voltage. Then after removing Q1, verified rail voltage.

Seems like the same result with jumpers in or not in when Q1 is installed.

 

[Perry Babin]

Do you have positive rail?

 

[Rabbit 16v]

No. no rail voltage on either side.