Got a strange failure here. I'm troubleshooting the power supply in my Super Bagman. It's a Stern PS-1200 (rev H). Without the game PCB connected to the supply, the +5V output is adjustable from 4.6 to 6.1V. But when I connect the PCB to the supply the +5V goes *UP* to 8V.
!!!
+5V goes up when loaded!
!!!
Anybody know what would cause this? As far as I can tell, the power transistor is good. I put in a new LM317 regulator. I don't have an ESR meter, but the caps seem ok. No opens and no shorts, values are all close. I pulled the fuses for the +12V and -5V supplies so the +5V section is running by itself.
One other thing...when I got the game R8 (22 Ohm) was burned but still measured about 24 Ohms. I left it in. The power trace going from R8 to the transistor was also toasted. I fixed that and the game ran fine until the flyback blew about 6 months later. It has been sitting for a couple of years now. I finally found a flyback replacement, fixed the monitor, and powered the game only to find that the PS was dead. Tried replacing R8 with two 43's in parallel tonight, but no change.
I don't have any spare PNP TO3 transistors....I tried subbing a TIP42C, but got the same behavior. Gonna try to get another transistor tomorrow. I think NTE219 is the cross. I'm stumped.
Oh yeah...I should state that I'd like to keep the game original so putting a switcher is not my first choice.
!!!
+5V goes up when loaded!
!!!
Anybody know what would cause this? As far as I can tell, the power transistor is good. I put in a new LM317 regulator. I don't have an ESR meter, but the caps seem ok. No opens and no shorts, values are all close. I pulled the fuses for the +12V and -5V supplies so the +5V section is running by itself.
One other thing...when I got the game R8 (22 Ohm) was burned but still measured about 24 Ohms. I left it in. The power trace going from R8 to the transistor was also toasted. I fixed that and the game ran fine until the flyback blew about 6 months later. It has been sitting for a couple of years now. I finally found a flyback replacement, fixed the monitor, and powered the game only to find that the PS was dead. Tried replacing R8 with two 43's in parallel tonight, but no change.
I don't have any spare PNP TO3 transistors....I tried subbing a TIP42C, but got the same behavior. Gonna try to get another transistor tomorrow. I think NTE219 is the cross. I'm stumped.
Oh yeah...I should state that I'd like to keep the game original so putting a switcher is not my first choice.
