I've finally got some resemblance of a workbench set up again to it's time to start looking at some faulty boards. First up a Stern Bagman.
Symptoms: Dead/garbage on screen
Repair: replace EPROMS at 9E, 9F, 9J, 9K, 9N, 1C and SRAM at 1S
First plug in, voltages ok. Garbage on screen, poked the reset pin of the Z80 with the scope and it was in a watchdog reset cycle.
Checked the first EPROM at 9E and it was duff, replaced, now signs of life...
...but not exactly perfect! Screen messed up, couldn't start a game, attract mode not going all the way through. Further probing of the Z80 reset pin indicated that the game was booting but crashing when it got onto the game screen. So checked the rest of the game ROMs and while I think they were OK they were unfortunately and earlier revision to anything in mame so I had to burn new another 4 out of the remaining 5 so I had an matching set.
Game now plays, but the graphics messed up...
Check the graphics ROMs, the first one at 1C was bad, looking much better... but there's still a small graphics glitch, in this picture you can see a few red lines a way down the screen under the mine cart, a similar red shadow under the lift on the second screen and there were a few other small glitches.
Kinda felt a bit ram related, luckily they're all in sockets on the Stern boards. Most likely the 82S16 SRAMs at 1P, 1 R, 1S, 1T.
I tried swapping them about to see if the problem moved, when I swapped 1S, 1T the glitch turned yellow so we're onto something. Swapped one of them out and all seems ok. Need to order some replacements though as I had to borrow one from another board.
Symptoms: Dead/garbage on screen
Repair: replace EPROMS at 9E, 9F, 9J, 9K, 9N, 1C and SRAM at 1S
First plug in, voltages ok. Garbage on screen, poked the reset pin of the Z80 with the scope and it was in a watchdog reset cycle.
Checked the first EPROM at 9E and it was duff, replaced, now signs of life...
...but not exactly perfect! Screen messed up, couldn't start a game, attract mode not going all the way through. Further probing of the Z80 reset pin indicated that the game was booting but crashing when it got onto the game screen. So checked the rest of the game ROMs and while I think they were OK they were unfortunately and earlier revision to anything in mame so I had to burn new another 4 out of the remaining 5 so I had an matching set.
Game now plays, but the graphics messed up...
Check the graphics ROMs, the first one at 1C was bad, looking much better... but there's still a small graphics glitch, in this picture you can see a few red lines a way down the screen under the mine cart, a similar red shadow under the lift on the second screen and there were a few other small glitches.
Kinda felt a bit ram related, luckily they're all in sockets on the Stern boards. Most likely the 82S16 SRAMs at 1P, 1 R, 1S, 1T.
I tried swapping them about to see if the problem moved, when I swapped 1S, 1T the glitch turned yellow so we're onto something. Swapped one of them out and all seems ok. Need to order some replacements though as I had to borrow one from another board.
