Dead Bomb Jack

[big10p]

Was working fine until I fitted a high score save and freeplay mod, now it's completely dead. Zero sound or video. I replaced all the original chips but it's the same, so I guess I broke something along the way. ☹️

Voltages seem fine and I probed the CPU which does look like it's active.

Any idea what could have broken that's killed it so completely?

 

[Georgian2]

Did you remove other roms? Bent pins on ICs is an common problem that happens when insertig an IC.

 

[big10p]

Did you remove other roms? Bent pins on ICs is an common problem that happens when insertig an IC.

I'm usually very careful when fitting ICs but I will check. I think I may have removed a different ROM to do a romident.

Just remembered that when I probed the CPU, the RESET pin looked like it was pulsing (not really sure how to use my probe properly, so not totally sure). Does that mean something is constantly causing it to reset?

 

[Georgian2]

If the reset is pulsing, it means the program is not running. Maybe you swapped the eproms or something like that

 

[big10p]

If the reset is pulsing, it means the program is not running. Maybe you swapped the eproms or something like that

I'm sure the ROMs are in the right place as they're all numbered in sequence. I think I'll try verifying them all with the MAME romset tomorrow.

 

[big10p]

OK, all the ROMs verify with the MAME ROMset.

I now realise that the D780C CPU that I probed on the top board is probably just used for sound? There's another one on the bottom board which looks like it's functioning. RESET pin is high and I'm getting pulsing on all data and address pins, except A15 which is constantly low, but maybe addressing isn't getting high enough to use it? Just guessing. I tried swapping out the CPU for a spare Z80 I have, but made no difference.

Pretty much stumpted, now. Anything else I can check?

 

[sukhbir]

Check the CS,OE,RW pins on 1E and 1H of the work rams,they should have activity. Also close to the work rams should be 5 program roms,Check the CS pins on all they should also be busy.

 

[philmurr]

What did the high score save/freeplay mod consist of?

Can you post a photo of the board now with everything replaced back to standard?

 

[big10p]

What did the high score save/freeplay mod consist of?

Can you post a photo of the board now with everything replaced back to standard?

I did the mod using Arcade ROM Patcher which patches ROMs 9 and 11, and requires the ram at E1 be replaced with a DS1220.

Bottom board


Top board

 

[Georgian2]

Cables are not plugged all the way in?? Press them on both boards.

I did the mod using Arcade ROM Patcher which patches ROMs 9 and 11, and requires the ram at E1 be replaced with a DS1220.

Bottom board
View attachment 50850

Top board
View attachment 50851

 

[philmurr]

Should the boards not fit back-to-back (so solder side go together, whereas you have them plugged in "backwards")?

I don't know for certain as I've never owned one, but that's how boards usually are

 

[big10p]

Cables are not plugged all the way in?? Press them on both boards.

I just tried again making sure they're all plugged in fully, but no change. ☹️

 

[Georgian2]

Should the boards not fit back-to-back (so solder side go together, whereas you have them plugged in "backwards")?

I don't know for certain as I've never owned one, but that's how boards usually are

Good eyes! My bootleg set is solder side to solder side.

 

[Bods]

Should the boards not fit back-to-back (so solder side go together, whereas you have them plugged in "backwards")?

I don't know for certain as I've never owned one, but that's how boards usually are

Yeah it should be on these, not all pcbs but yeah good spot

The old saying a Picture is worth a thousand words is certainly the case here or hours/days of head scratching

 

[big10p]

Should the boards not fit back-to-back (so solder side go together, whereas you have them plugged in "backwards")?

I don't know for certain as I've never owned one, but that's how boards usually are

OMG, I didn't even consider that. I can't seem to find a good enough pic of the board online to confirm. Should I just try it?

 

[Bods]

https://www.ebay.co.uk/itm/197796173231

 

[Georgian2]

Here is a pic of my bootleg. I consider it to be 1:1 like original.

 

[big10p]

Here is a pic of my bootleg. I consider it to be 1:1 like original.

Thanks. I'll give it a go then. Trust me to cock up something simple. 🙆‍♂️ God knows what damage it's done...

 

[Lurch666]

If you have a multimeter check the +5 and GND from the edge connector to a ttl on the bottom PCB.
Don't just try it in case it messes something up.

 

[big10p]

Yep, that was the problem. 🫣 Thanks, Phil. 👍 Luckily, it seems to still work!

Now to see if the HSS mod works. Cheers, all.