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

[neonarossa]

The rail voltage is "+118.9/-118.9". I have a distorted signal on (pin#12) counting from right. The ic's id# is buffed out. I don't know the pin layout for the driver board?? I enclosed the signal in, driver board signal (pin#12) etc.. thanks..

 

[Perry Babin]

See attached.

The driver ICs are IR21844S/IRS21844S.

 

[neonarossa]

See attached.

The driver ICs are IR21844S/IRS21844S.

This is my first Sundown.. Thanks Perry..

 

[neonarossa]

I checked the two IRS21844s chips using the resistance guide.
U1>> 6/5=24.65k 6/7=24.65k 7/5=5.4
12/13=.383m 12/11=24.6k 13/11=1.1m
With pin#7 lifted
trace: 7/5=9.2 leg: 7/5=348.3k leg: 6/7=.379m

U2>> 6/5=24.55k 6/7=24.55k 7/5=5.5
12/13=.373m 12/11=24.5k 13/11=1.28m
With pin#7 lifted
trace: 7/5=9.2 leg: 7/5=.949m leg: 6/7=.964m

What is a possible alternate to check? Thanks

.

 

[Perry Babin]

When you list something like that, list each separate item on its own line. Like:

U2>>
6/5=24.55k
6/7=24.55k
7/5=5.5

You could have a defective 12v regulator or a defective capacitor across 5 and 7.

 

[neonarossa]

Ok.
L7812.
Pin1= -93.1v
Pin2= -111.9v
Pin3= -111.1v
L7812A
Pin1= -93.1v
Pin2= -111.9v
Pin3= -111.1v

They appear completely out of range. The amp is not in protect?? Thanks

 

[neonarossa]

C12, C13= 9.3ohm
CL2= 9.2ohm
What is their value? Thanks

 

[Perry Babin]

Is that what they read off of their pads?

 

[neonarossa]

Yes.

 

[neonarossa]

Yes.

The l7812 were measured with -lead on rca shield.

 

[Perry Babin]

When measuring the voltage on the L7xxx type regulators, place the black probe on the ground terminal of the regulator (different terminals, for L78xx and L79xx types) and the red on the other two terminals.

The ones you posted the voltage for need to be removed and checked (to see if they're shorted) out of the circuit.

 

[neonarossa]

L7812 & L7812a were shorted.

With regulators removed.
L7812 pin#2 to 1=open
pin#2 to 3=49.6ohm

L7812a pin#2 to 1=123ohm
pin#2 to 3=11.2ohm

pin#1 input=18.8v
pin#3 output=.8v

U1 7/5 was 9.2 Now 6.53k
U2 7/5 was 9.2 Now 6.64k
Will just the regulators need replacement?

 

[Perry Babin]

I'd expect there to be more damage.

Is the capacitor across pads 5 and 7 of the driver IC leaky/shorted?

Do you have signal reaching the input terminal of the driver board?

Do you have a spare 10k resistor?

 

[neonarossa]

So did I.
Cl2 & Cl3=1240uf>> measured on fluke11<<
Yes.
Yes.
Input 100hz.
Output to pin#12 on driver board

 

[Perry Babin]

CL2 and CL3 are more likely to be something like 0.1uF. What's the resistance across them out of the circuit?

Did you measure their capacitance out of the circuit?

Pin 12 is the -5v input. Refer to the diagram that was posted.

 

[neonarossa]

Cl2=.043uf
Cl3=.026uf
There was no resistance reading. Was using Mohm.

Yes there is signal on pin#10 on the driver board.
I was using pin#12 from right side. (i had the pin out backwards)..

 

[Perry Babin]

Solder the 10k resistor to one green point and one yellow point (whichever are easiest).

After the resistor is in the circuit, you should have audio on pin 1 of the TL072 and a square wave swinging ±5v on the output of the LM211.

 

[neonarossa]

Have audio on tl072 pin#1
Have square wave on lm211 pin#7

 

[Perry Babin]

What does the waveform look like on pin 1 of either of the 21844 driver ICs?

 

[neonarossa]

This is with both pin#7 lifted.