TP2 at 7V

[Tibuck19]

Possibly to high damping R.

as it stand I took off the R1 and its on a variable resistor. but if I lower the resistor value I lose all sensitivity.

[green]

Have you looked at the +and-5v with a scope? Don't see how can get 7v unless 78L05 is bad or leakage across input to output pins of 78L05.

[Tibuck19]

Have you looked at the +and-5v with a scope? Don't see how can get 7v unless 78L05 is bad or leakage across input to output pins of 78L05.

I replaced the 78L05 and went around the board re-soldering and cleaning with IPA just to make sure, the single seems to be coming for the power supply I think ?

[Mdtoday]

I replaced the 78L05 and went around the board re-soldering and cleaning with IPA just to make sure, the single seems to be coming for the power supply I think ?

Sounds like you have a broken common connection to the 5v regulator.

Brian

[Tibuck19]

Maybe this could help solve the problem, R21, 10K is reading as 8K and r22 56K is reading as 22K. And they are the correct resistors.

[green]

Maybe this could help solve the problem, R21, 10K is reading as 8K and r22 56K is reading as 22K. And they are the correct resistors.

Why would R21 and R22 effect +5v supply? Maybe a stupid question, what voltage would you read if the 78L05 was connected reversed?

[Tibuck19]

Why would R21 and R22 effect +5v supply? Maybe a stupid question, what voltage would you read if the 78L05 was connected reversed?

I'm looking for the problem and going around the hole board and those two resistors are the only two that are off specs and even after testing a new resistor (47K which is the closes I have) and replacing it , it still drops down to 22K, the 78l05 is in the correct way unless its a slik screening error which is next to impossible.

[Qiaozhi]

I'm looking for the problem and going around the hole board and those two resistors are the only two that are off specs and even after testing a new resistor (47K which is the closes I have) and replacing it , it still drops down to 22K, the 78l05 is in the correct way unless its a slik screening error which is next to impossible.

What are the voltages on the 78L05 outer pins with reference to the middle (0V) pin?
I know they should be the same as when you measured them with reference to TP10, but just humor me.

[Tibuck19]

What are the voltages on the 78L05 outer pins with reference to the middle (0V) pin?
I know they should be the same as when you measured them with reference to TP10, but just humor me.

George, the exact same voltage get from TP10 the output pin is at 12V using the input as -0V and the common pin is at 7V . this might be normal loll but when i have the probs on TP3 and try putting thr ground lead on TP10 I get a tiny spark, It has to be something Silly

[Qiaozhi]

George, the exact same voltage get from TP10 the output pin is at 12V using the input as -0V and the common pin is at 7V . this might be normal loll but when i have the probs on TP3 and try putting thr ground lead on TP10 I get a tiny spark, It has to be something Silly

In that case, it looks like the 78L05 must be faulty ... OR, there's a short somewhere that's putting 7V on the output pin. I would try disconnecting the 78L05 output pin (just snip it off with some side cutters) and measure the voltage between TP10 and the dangling output wire of the 78L05. I suspect you'll find it's +5V. If not, it's faulty. Then measure the voltage between TP10 and the pad where the wire was originally connected. Is it +7V?

[Tibuck19]

In that case, it looks like the 78L05 must be faulty ... OR, there's a short somewhere that's putting 7V on the output pin. I would try disconnecting the 78L05 output pin (just snip it off with some side cutters) and measure the voltage between TP10 and the dangling output wire of the 78L05. I suspect you'll find it's +5V. If not, it's faulty. Then measure the voltage between TP10 and the pad where the wire was originally connected. Is it +7V?

George im sorry I looked at the wrong one the 78l05 AKA U3 is at 7 and 9 V and I keep saying the 78l05 when I mean the 79l05 ,Gesss am I ever going to get it right for pete-sake loll , As I mention before I already replaced the 79l05 U1 not the 78l05

[Qiaozhi]

George im sorry I looked at the wrong one the 78l05 AKA U3 is at 7 and 9 V and I keep saying the 78l05 when I mean the 79l05 ,Gesss am I ever going to get it right for pete-sake loll , As I mention before I already replaced the 79l05 U1 not the 78l05

OK ... now I'm totally confused, and probably so is everyone else.

Please can you re-state the current situation with the power supply voltages. Which ones are correct, and which ones are wrong?
What do you mean by "78l05 AKA U3 is at 7 and 9 V"?

[homefire]

Dang. Measure the Voltage across the Regulators. . In/Out.. You should see Your supply voltage Minus the rated voltage. Anything less would indicate Shorted Regulator. Any thing more indicates Bad Regulator or Resistance on the control pin.

[Tibuck19]

OK ... now I'm totally confused, and probably so is everyone else.

Please can you re-state the current situation with the power supply voltages. Which ones are correct, and which ones are wrong?
What do you mean by "78l05 AKA U3 is at 7 and 9 V"?

OK! Sorry if I got you all confused, I am getting 7V on TP2 When I measure with TP10, on 79L05 which is located on U1 I get 12V on the input and 7V on the common using middle pin as gound, Measuring 78L05 which is located on U3 i'm getting 7V output and 9V on the input using middle pin as ground . I am using a multimeter and not the oscop for these readings.

[homefire]

on 79L05 which is located on U1 I get 12V on the input and 7V on the common using middle pin as gound /// 12 - 7 = 5 GOOD

Measuring 78L05 which is located on U3 i'm getting 7V output and 9V on the input using middle pin as ground/// 9 - 7 = 2 Toast Your getting 2 Volts to much thru the Regulator. Replace it.