Eyebrid 1y2000 Problem

[Achim1409]

Hello, i have buyed this amp.
Amp is in Protect. LED lids only very weak red. Obvisiosly no parts are damaged. If i ground Pin3 from TL 494, the amp powers up and produces rail.
But its not stable.
The Output from TL 494 goes for each bank on a MC34151. ,
The first seconds everything is ok, then the Amplitude out of the 34151 starts drop a little bit and the frequency changes.The VCC Pin 6 is also going high and low a few volts all the time. If remote is connected, i have 9V, if i ground Pin 3of 494 it drops between 6-5VDC.
I have removed the Audio driver board, and the outputs from the 7912CV and 7812CV because the got hot. Still the same.
Found also, that on Pin12 of the 494 is with remote applied only 9VDC



With the Audio driver board inside i have no DC on the Outputs. But also no Oscilation on the Output fets.



Any suggestions?

 

[Achim1409]

On the B649AL Pin 1 goes Remote 12V, Pin 2 goes to Pin12 494, only 8,8V
So i expect, that the transistor is damaged??? I will remove now an check.

 

[Achim1409]

Removed, and its damaged. Shows as common junction zener diode.... Which one i can take as replacement?

 

[Achim1409]

I have changed the Transistor with a B631K for test. Voltage is a little higher, so i expect, something is pulling the voltage down...

Any suggestions?

 

[Perry Babin]

What is the voltage on the input terminal of the switching transistor?

 

[Achim1409]

If i remove the transistor, and apply remote, i measure on Pin 1 12V, Pin2 0V, Pin 3 2,9V.
Without remote: Pin 1 12V, Pin2 0V, Pin 3 12V.
If i bridge pin 1 and 2 with remote applyed, the Amp sometimes switch on.

 

[Perry Babin]

As the amp was after replacing the transistor with the transistor in place and the remote applied (amp on), what are the voltages. Please list in vertical column instead of inline.

 

[Achim1409]

Pin 1: 12V
Pin 2: 12V
Pin 3: 11,6V
Amp is turning on now...???

 

[Achim1409]

Is turning on only if i connect the remote secon time. It wants to turn on at first time, but changing from green to red. Second time it switching on.

 

[Perry Babin]

For the 'first time', do you have B+ and ground connected and then apply remote?

 

[Achim1409]

If iam Looking for the Part number of the original transistor it shows me also a triode with the same part number. But on the board its marked as Q.. So iam not shure is the part ok or not. If its a triode,it should be ok.

 

[Achim1409]

Yes, always B+ is connected. Then i try remote. Only at the second time it powers up. It seems, that something is not switching or charging fast enough.

 

[Perry Babin]

2sb649?

What if you wait longer to apply remote?

 

[Achim1409]

UTC SFA1
B649AL C


No the led slowly goes to green and then red and stays there. Only if i remove remote and aplly directly again then it switches on.
Rechecked: If i left it longer then it starts.

 

[Perry Babin]

I think you'll have to look at the voltages on the comparator and 494 to see what's different when the amp comes on and when it doesn't.

 

[Achim1409]

When the LED is red, i have on Pin 3 5V, when its green, 0V, so i think undervoltage protection. I will check the voltages on the comparator now.

 

[Achim1409]

When its on:
1: 0V
2: 3,38V
3: 0V
4:0V
5:0V
6: 4,95V
7: 0V
8: 9,5V


I think the supply is too low.

 

[Achim1409]

Ok, Comparator LM 358:


On
Pin1: 0V

Pin2: 3,38V
Pin3: 0,89V
Pin4: 0V
Pin5: 0V
Pin6: 4,95V
Pin7: 0V
Pin8: 9,5V




Protect:
Pin1: 0V
Pin2: 3,36V
Pin3: 0,89V
Pin4: 0V
Pin5: 8,9V
Pin6: 4,95V
Pin7: 9,38V
Pin8: 10,5V

 

[Perry Babin]

What drives pin 5?

What does pin 7 drive?

 

[Achim1409]

Pin 5 goes to the Protection Board close to the relays.
Pin 7 goes over a diode to a resistor, than optocopler to pin 1 of 494.


If i remove the protection board, the amp switches on, but the relays dont engage.
So i think this is dc protect and the power supply for the relays.