Bought this as a broken board/abandoned repair attempt. Seller said it was giving a picture but restarted continuously. He also claimed it was recapped and cleaned from battery corrosion.
Board started up to a static corrupt screen. Noticed that pin94 on neo b1 (watch dog enable) had a wire to ground. Removed it and got a click of death.
Probed the bios chip. Noticed an offset on adress pins 1-8. Suspected a 74as245 chip on the bus since it was close to the battery. Removed and put in an empty socket. The off set was gone. Replaced with a ls245 since I hade no as245 at home. Offset came back so the AS/LS245 was probably tri-stated and I had done a lot of work for no reason. Also broke one pin on the somewhat rare as245 chip. So things got actually worse by doing all this work. LOL.
Probed adress lines a17-21 on the cpu. These had a terrible off set. Suspected another as245, this one located directly beside the battery. Replaced this chip with another socket and ls245. Booted to "calender error". (And of course; the broken chip could be desoldered without any damage.)
Replaced the calender crystal because it was dead. This however didn't fix the calender error. Looked around the 4990-chip. Found and patched two broken traces. Booted to cross hatch.
Ran a game (still with the ls245 instead of as245). All slots were working but sound was kind of unbalanced. First I thought the amplifier was toast or that something was wrong with the recap-work.
Then it struck med that there was no mono/stereo-switch. Ran the board in a stereo cabinet and everything sounded as it should.
Next step was to clean up the battery corrosion more thoroughly. Started to remove the somewhat forced-to-fit battery holder.
Removed all components and then took turns with toothbrush, vineagar, distilled water, baking soda and fine grit sand paper.
(The backup-crystal area was cleaned and sanded later on)
Then applied 2 layers of UV-coating and repopulated the circuit.
I couldn't find a battery holder that fit the existing holes. Alternatives are: drill a new hole (never!), use wire, design a simple adapter board or use a cased battery holder with wires. I ended up ordering a cased battery holder since this will let one change battery without the need to disassemble the board. Also ordered as245-chips and felt the satisfaction of bringing another beautiful MV4F-board back to life.
Board started up to a static corrupt screen. Noticed that pin94 on neo b1 (watch dog enable) had a wire to ground. Removed it and got a click of death.
Probed the bios chip. Noticed an offset on adress pins 1-8. Suspected a 74as245 chip on the bus since it was close to the battery. Removed and put in an empty socket. The off set was gone. Replaced with a ls245 since I hade no as245 at home. Offset came back so the AS/LS245 was probably tri-stated and I had done a lot of work for no reason. Also broke one pin on the somewhat rare as245 chip. So things got actually worse by doing all this work. LOL.
Probed adress lines a17-21 on the cpu. These had a terrible off set. Suspected another as245, this one located directly beside the battery. Replaced this chip with another socket and ls245. Booted to "calender error". (And of course; the broken chip could be desoldered without any damage.)
Replaced the calender crystal because it was dead. This however didn't fix the calender error. Looked around the 4990-chip. Found and patched two broken traces. Booted to cross hatch.
Ran a game (still with the ls245 instead of as245). All slots were working but sound was kind of unbalanced. First I thought the amplifier was toast or that something was wrong with the recap-work.
Then it struck med that there was no mono/stereo-switch. Ran the board in a stereo cabinet and everything sounded as it should.
Next step was to clean up the battery corrosion more thoroughly. Started to remove the somewhat forced-to-fit battery holder.
Removed all components and then took turns with toothbrush, vineagar, distilled water, baking soda and fine grit sand paper.
(The backup-crystal area was cleaned and sanded later on)
Then applied 2 layers of UV-coating and repopulated the circuit.
I couldn't find a battery holder that fit the existing holes. Alternatives are: drill a new hole (never!), use wire, design a simple adapter board or use a cased battery holder with wires. I ended up ordering a cased battery holder since this will let one change battery without the need to disassemble the board. Also ordered as245-chips and felt the satisfaction of bringing another beautiful MV4F-board back to life.
