Got this original Juno First (by Konami) for a repair :
Board played fine but some sounds were missing, the most noticeable was the laser shot:
Here is a MAME record for a comparison:
All the sounds are generated by the AY-3-8910 chip.Probing it revealed that three I/O (pin 19-20-21) were stuck high, these should exchange data with same number of I/0 lines of the Intel 8039 MCU like shown in schematics:
The 8039 was dead, clock was missing on pin 2 and 3.I replaced the 8MHz quartz and the two 10pF capacitors with no change.This MCU has no internal ROM so it needs an external one :
Using a dummy ROM file in MAME reproduced exactly the issue, some sounds were missing like in my board.This lead me to think the MCU was bad so I removed it:
The 8039 is not widely used on arcade system but I was luck and found one on a Gyruss bootleg.Installed a socket and chip:
and all mssing sounds were back.End of job.
2 Responses to “Juno First repair log #4”
Sorry, the comment form is closed at this time.
Great stuff, just got one question: is that a 6Mhz CPU running on a 8MHz quartz ?
Yes, the M5L8039P-6 can accept clock up to 6MHz but this was only for a test.