PTC MSX PC - cartridges not working - need help troubleshooting

Supporter (8)

29-09-2021, 11:54

Hello, all.

I acquired a PTC MSX PC ISA card recently, but seems it's not 100% functional. Trying to get it repaired but having a tough time. Would appreciate if any of the MSX "gurus" could help with the troubleshooting.

First of all, here's what's working:

- With no cartridge inserted, PTC MSX boots OK to BASIC.
- I have Puyo Puyo on floppy disk. If inserted, it boots OK and plays 100% fine: graphics, audio, gameplay all OK.

With a standard MSX cartridge inserted, only a black screen is shown on the PTC MSX. I own two cartridges, they test OK on a standard MSX machine.

With a MegaFlashROM cartridge inserted, behavior is different: the PTC MSX reboots several times. Eventually, it boots into MSX BASIC and displays "Syntax error in 0" - if "list" is typed, random bits of code are then displayed.

My engineer friend is doing the repairs. He surmised that the card was at one time damaged by the cartridge adaptor having been plugged in backwards.

Here's the repair process...

- The card was carefully checked for any shorts.
- The cartridge adapter pins were replaced with a keyed connector.
- All 74 series logic chips were replaced with new ones.

After all this, there was no change: cartridges still don't work. Then...

- The Yamaha S3527 was replaced with a tested, working part.

This changed the behavior slightly: standard carts still boot to a black screen. But the MegaFlashROM now displays the same exact code every time "list" is typed after the "Syntax error" message. Before the S3527 was replaced, the code was always random. Sadly this obviously still leaves me with no cartridge support.

Here's two photos: the first shows the display before S3527 was replaced. Second shows the display after.

As I'm sure y'all know, the PTC MSX card is not easy to come by. It's important to me that it's properly restored to fully working condition, so I can not only enjoy it to its fullest, but also do research and documentation about it.

Any help appreciated. Anyone's welcome to get in touch with me by e-mail; the link is at the very bottom of my diskman.com website.

Thanks in advance,

- Brandon

Aangemeld of registreer om reacties te plaatsen

Van DeathAdderSF

Supporter (8)

29-09-2021, 12:00

I neglected to mention the capacitors have also been replaced with brand new ones.

Van sdsnatcher73

Prophet (3951)

30-09-2021, 02:46

It’s tough to say what is causing this. Are you sure the cable and cartridge connector are good? Dirt in the connector may be a cause for strange behavior. It’s probably good to start analyzing the signals on the card when you get the black screen. That is not normal so there has to be something that can be observed. Is the CPU active at such point, is the reset or wait signal active, compare your findings with what is happening on a MSX that is working and also when there is no cartridge inserted.

Van sdsnatcher73

Prophet (3951)

30-09-2021, 02:50

Seeing that MFR boots it may be the address or data lines that cause issues. Is your MFR equiped with 512kB RAM? This RAM will be the active RAM when it is inserted, so problems on the address/data could result in bad read/write to this memory.

Does the boot screen show with the game carts before you get the black screen?

Van sdsnatcher73

Prophet (3951)

30-09-2021, 03:09

Are you sure the cable orientation is correct now? Check the signals are as expected on the cartridge slot side. Probably good idea to start with this.. also not having an insertion protection on the slot can cause wrong insertion (up side down) so it may be a good idea to look at https://github.com/RBSC/FLEX

Van st1mpy

Paladin (932)

30-09-2021, 09:23

On the cartridge slot, is the 5v pin working? Gnd?

Van MSX4ever

Master (253)

03-10-2021, 01:54

Hi Brandon,
As you already heard, I also have a PTC card in my possession.
I also have an MSX slot with the MFR cartridge attached to the PTC card. It works properly. If I need to measure or test something, I'd love to hear it.

MSX4ever.