Bally Pro Arcade

[daver2]

I think you have probably answered your own question there!

Dave

 

[falter]

I got the cap kit from Allen of Ballyalley. After replacement, I now have +12v and no smoke. Also -5v. But +5v is coming up at zero. If I understand the schematic right the 5v comes from a ua78gu1c regulator. I have tested the pins.. the In pin is getting 22v. VOUT is -1v, and CONTROL is 0v. This would indicate either VR failure or a short (it is going into protection mode?). I've checked the RAM chips.. they have +12v at VDD and -5v at VBB and of course 0v at VCC. I'm not sure if these had a short if it would have shown the wrong voltage at VCC? I assume it would and the chips would fry?

 

[daver2]

Don't forget that the actual +5V supply is sourced by transistor Q1.

So measure the base, emitter and collector of Q1 also.

The voltage regulator itself does not actually supply any load itself in this configuration.

Dave

 

[Agent Orange]

How difficult would it be to pull Q1 ( a NPN I think) and check the front to back between emitter-base-collector (round robin & greater than 10 to 1). Also, what is VR3?

 

[daver2]

>>> Also, what is VR3?

See post #82.

Dave

 

[Agent Orange]

>>> Also, what is VR3?

See post #82.

Dave

Thanks - hiding in plain sight.

 

[Dokken]

I got the cap kit from Allen of Ballyalley. After replacement, I now have +12v and no smoke. Also -5v. But +5v is coming up at zero. If I understand the schematic right the 5v comes from a ua78gu1c regulator. I have tested the pins.. the In pin is getting 22v. VOUT is -1v, and CONTROL is 0v. This would indicate either VR failure or a short (it is going into protection mode?). I've checked the RAM chips.. they have +12v at VDD and -5v at VBB and of course 0v at VCC. I'm not sure if these had a short if it would have shown the wrong voltage at VCC? I assume it would and the chips would fry?

I have had a Bally with similar symptoms (no +5v, no video) that I've been farting around with for a couple of years. I finally sent it off to Allen S. in Kansas who owns a Balcheck diagnostic device. He identified the bad RAM chip within 20 minutes of receiving it and had it scribbling!. Very, very reasonable cost. let me know if you want the contact info. Highly recommended.

 

[falter]

I removed the TIP31 as I couldn't figure out where R2 was (was just going to disconnect one side of that to test the TIP31 without removing it).

There are no shorts between B C and E, and in diode mode my DMM registers .6v between B and E and B and C, on the nose, one way and zero the other.

So I think we can rule that out?

I'm thinking RAM may be a good culprit here even though if I test the various power pins I'm not seeing anything shorted..

 

[falter]

Hmm.. I wonder if the recently redrawn schematic is incorrect. It shows pin 2 of the TIP31 connected to R2, however, if I follow pin 1, I immediately find what looks like a 200ohm resistor there (tests as 240ohm). The data sheet shows pin 2 is in the middle facing front of the TIP31, but the leg that is connected to that resistor is pin 1.

 

[daver2]

Let's do the simple thing first...

What is the unregulated DC voltage across capacitor C6?

This feeds the collector of Q1 and is the actual supply used for the +5V rail.

The control pin of VR3 is actually an INPUT to VR3. It measures the rail voltage and adjusts the output voltage (feeding the base of Q1) to control the sense pin of VR3 at +5V.

Dave

 

[falter]

Let's do the simple thing first...

What is the unregulated DC voltage across capacitor C6?

This feeds the collector of Q1 and is the actual supply used for the +5V rail.

The control pin of VR3 is actually an INPUT to VR3. It measures the rail voltage and adjusts the output voltage (feeding the base of Q1) to control the sense pin of VR3 at +5V.

Dave

C6 is showing +11.5v

 

[daver2]

So that supply is working OK.

Dave

 

[daver2]

Did you ever have a correct reading for the +5V rail?

Can you post a good photograph of the top and bottom of the PCB showing VR3 and Q1 (and the surrounding components) please so I can trace the PSU schematic out by hand.

Dave

 

[falter]

Can you post a good photograph of the top and bottom of the PCB showing VR3 and Q1 (and the surrounding components) please so I can trace the PSU schematic out by hand.

Dave

Attached.. hope I got enough detail.

Did you ever have a correct reading for the +5V rail?

It's been a while but I'm pretty sure I tested +5v ok back in December when I was first probing about. But I was really focused on the 12v regulator that kept smoking up so not 100% on that.