Sundown SCV-4000D. No output from audio driver board

[Perry Babin]

That should have an amplitude of about 10v.

Confirm that it's swinging all of the way to the negative rail. If it is, switch to AC coupling and check the amplitude at a lower vertical amplifier setting.

 

[neonarossa]

The l7812 are not in, if it matters..

 

[Perry Babin]

It should not. The drive is dependent on the 5v and the negative rail. You have drive. Now you have to determine if it's of sufficient amplitude.

If you believe that the un-powered IC is loading the drive circuit more than it should, lift pin 1 to remove the IC from the drive circuit.

 

[neonarossa]

It swings to negative rail.
Set to AC and measured.

 

[Perry Babin]

With your meter, measure the AC voltage on the output of the LM211. Black probe on the audio ground pin of the driver board. This is for reference.

Then measure the voltage on pin 1 of the 21844 with the black probe on pin 3 or 5 of the 21844.

Post the voltage you read for both.

 

[neonarossa]

The problem is the ir218442.
U1 & U2
With pin#1 connected output is appx 1.5v.
Without pin#1 connected output is close to 10v.

 

[neonarossa]

yes. that is both IR21844s..

 

[Perry Babin]

I have to check something. I have an amp here that uses the 21844. I'll pull the regulator to see if it loads the drive circuit. It's something that I've never had to try.

 

[neonarossa]

5.36v.a/c LM211 output.
U1= .004v>>pin#1(pad)
U2= 7.04v>>pin#2(pad)

Pins #1 & #7 are off the pads..

 

[Perry Babin]

Did you mean pad 1 for both ICs?

The IC does load the drive signal more when it doesn't have its 12v supply. You can check the signal on the non-IC side of the 10k resistor that's in series with pin 1.

 

[neonarossa]

yes.
Replace the regulators and retest?
The IR21844s are still good?

 

[Perry Babin]

I haven't seen anything that shows them to be defective.

Have you seen the posts about low-voltage testing by adding windings to the main transformer?

You could replace the regulators and power up normally or use the low-voltage testing which gives the amp a better chance of surviving if there is a problem in the output stage.

 

[neonarossa]

No. I will read it.
Would the current limiter help?

 

[Perry Babin]

Start reading here and the next couple of pages:
4000.1

The B+ limiter doesn't help, many times, because the caps get charged and then the circuit is enabled. If there is a problem, the outputs may have to try to survive discharging all of that stored energy. Using the low-voltage significantly reduces the energy stored.

 

[neonarossa]

I will repost after the regulators are installed and tested. Thank you.

 

[neonarossa]

The regulators are in. Desolder the 10kR?
Should i lift the high & low pins of the 21884s and check signal or not needed?

 

[Perry Babin]

What condition is the amp in right now?

What parts are missing or disconnected?

What pins of what ICs are lifted?

Besides the 10k resistor, is there anything that's out of the ordinary (not covered by the previous questions)?

 

[neonarossa]

Great condition.
No parts off
Pin #1 & #7 are lifted on both 21844s
I now get +12v at the driver board pins. Although, i do not measure +12v at the #7 vcc pads no matter which ground reference i use. Maybe the 10kR affects this?

 

[Perry Babin]

Check continuity from the driver board pins to the capacitor across the 12v supply and to pins 5 and 7.

 

[neonarossa]

Continuity is good from driver board pins to Caps, #5pin,#7pad.
I measure 12v from l7812 tab to both ir21844s #7 pad.
I measure -100v from driver board ground & rca shield to #7 pad.