When the power button is depressed, the LCD display shows the normal "Stalker" splash screen but doesn't continue to power up. The unit powers down as soon as the power button is released. I found a leaking 22uf capacitor near the 5v regulator that had leaked onto the circuit board but replacing it didn't help. There is a 5v test point that reads 4.26v. The regulator is a LM2931CT and it's "adjust" lead appears to be not used and I don't find any pots on the circuit board. There is 100uf capacitor near the regulator that looks normal so I didn't replace it.
I guess my question is: does the 4.26V reading indicate a problem?

 

Strictly speaking (writing) the LM2931 does not have an adjust pin. It is fixed at 5.0V ±3.8%. It should not be reading 4.29V. Is anything getting hot, which would indicate faulty circuitry elsewhere is pulling the supply down?

 

Strictly speaking (writing) the LM2931 does not have an adjust pin. It is fixed at 5.0V ±3.8%. It should not be reading 4.29V. Is anything getting hot, which would indicate faulty circuitry elsewhere is pulling the supply down?

Great suggestion. I will check that later today.

 

Interesting....

I was looking at the National/TI version.

Is the one you are looking at the ON Semiconductor version?

 

Interesting....

I was looking at the National/TI version.
View attachment 132389
Is the one you are looking at the ON Semiconductor version?

It has the 5 leads. Would the output still be there if the 'out' lead was lifted from the circuit board?

 

Without seeing the full schematic I cannot say.

 

Hello,

The fixed versions of the LM2931 has 3 pins.
The adjustable version of the LM2931 has 5 pins.
Both the TI as ON datasheets will show the difference.

Bertus

 

Hello,

The fixed versions of the LM2931 has 3 pins.
The adjustable version of the LM2931 has 5 pins.
Both the TI as ON datasheets will show the difference.

Bertus

I couldn't find any technical information on this. The company went out of business a few years ago. I took a pic of the board with the regulator being on the left side.

 

Hello,

Could you make a picture of the corner with the regulator and the small smd parts around it?
If possible so that we can read the values on the smd resistors.
(I know that I can take pictures with my S5 that are that sharp).

Bertus

 

Hello,

Could you make a picture of the corner with the regulator and the small smd parts around it?
If possible so that we can read the values on the smd resistors.
(I know that I can take pictures with my S5 that are that sharp).

Bertus

I will try with my s4.

 

I tried the heat test. The regulator gets pretty warm where I have to remove my finger after about two seconds and the other chips do warm up but only enough to tell they are warm. The warmest other than the regulator is the large chip at the top of the board in the first picture. It is a Siemens SAB 80C535-N.

 

Regulators can run hot and still be fine -the maximum junction temperature of the die in this one is 150°C.

One test of the regulator that you might be able to perform is to measure the voltage between the output and the reference pin. Did you check the incoming power supply to make sure it is ok.

And while at the power supply connection, you can measure the input current and see how that compares to the label or manual if either is present.

 

Connections E1, E2, E3, E4, look like they are fatigued. E1 and E2 look poorly soldered. It might be the lighting ...

 

Connections E1, E2, E3, E4, look like they are fatigued. E1 and E2 look poorly soldered. It might be the lighting ...

That is where the control panel connects and you are right, they do look bad. I will try re-soldering those.