Recent content by cwispy

How are you getting on with your diagnosing the board? Have you found any more issues?

Just thought I would add another successful conversion to the list. Thanks to all involved in getting this working.

This ERDY pin is low when its performing a write operation which will only happen the once. Expand your search to include the 74LS253 IC's. The outputs from these also connect to data lines D0 - D7. Its likely one of these data lines is causing your problem.

This is roughly what you will see when you hold the test button down during power on. https://cwispy.com/sunset-riders-repair/

If you have access to an eeprom programmer and some replacement roms, you can program up the mask roms and piggyback them one by one. Alternatively you will need to use a logic probe to go around the pins on the roms to see if there are any legs that are not changing or are floating. The...

Interesting to hear that you had an eeprom failure. I have fixed literally hundreds of Konami boards which use that eeprom and I have never had to replace a single one. Every single time it has been one or more of the other IC's around it that has been the cause.

The Goldstar chips seem to be a little more reliable compared to the Fujitsu chips, but given that these boards are now over 30 years old, any IC is going to be running on borrowed time.

A lot of the times, you wont be able to just piggyback those old Fujitsu chips, you need to replace them or at least desolder legs to determine if they are holding signals high or low, but desoldering and getting them to not make contact is often harder that just removing the IC and putting in a...

That eeprom is only accessed very briefly during startup and then it is not accessed again. Are you getting anything on the Data Output (DO pin4) of the EEPROM?

Check out the SPI Region changer - SPI Revive https://www.arcade-projects.com/threads/seibu-spi-region-changer-spi-revive.7703/

If those boards use the same or similar customs as the Snow Bros boards, then a faulty custom ic would not be surprising at all. Sorry I can not really be more help.

Without knowing the boards better I cant say for certain that those rams do not have anything to do with the objects, but it would appear that they do not based on your image.

Well done finding the faulty 74ALS174. I would be very surprised if a 74LS174 wouldn't work in its place, as these boards generally do not run anywhere near the speed that an LS is capable of. All I can suggest is to continue doing what your doing to find the remaining faults. Good luck!

If 9C / 10C are a Fujitsu chips, it would not be the first time that I have seen them fail and pull down the data line. So in answer to your comment Yes any IC that is connected to the same signal can pull it down or up when it fails depending on how it has blown internally.

Looking at the circuit again, the rams at locations 14J and 14K appear to be colour rams. Unfortunately I am not familiar with that particular pcb. There is a lot of srams on that board according to the circuit. My best guess would be to start around the rams at 16A.