Defense Command (defender bootleg)

[mickyc22]

Anyone familiar with this board set, i have one and its failing to boot correctly so after some advice, i know its possible to run defender eproms on the board, but at present mine still has defense command in it. I also know there are 2 versions of this defence command and defense command mine is the latter with one ribbon cable. Google image below for reference.
It starts to boot get the boot pattern then nothing the 4 leds flash twice suggesting no standard errors but nothing on the screen, the test button on the eprom/sound board does kick off the defender type growl, and the bottom board button resets it.
i am aware of the defence command manual online but i know its somewhat different to my version although both are very similar to defender itself.
couple of my chips have lost their lettering so i like to compare with another board what they actually are, as i cant find any schematics for my version.
Any advice would be gratefully apricated.

 

[philmurr]

What test equipment do you have?

 

[mickyc22]

i have a scope/logic probe/multimeter but i dont claim to be an expert in using the scope or probe tbh

 

[cliff_poole]

I've got a working one of those, what chips do you need to know about ?.

For circuit diagram, it should loosely follow early Defender, except for component locations.

At least the RAM is all socketed. Try re-seating all the socketed chips first.

 

[mickyc22]

I've got a working one of those, what chips do you need to know about ?.

For circuit diagram, it should loosely follow early Defender, except for component locations.

At least the RAM is all socketed. Try re-seating all the socketed chips first.

thanks i dig out a picture of the chips im after in a bit, the ram wasn't socketed in mine but i have sweated them all out and tested them and now socketed them they were all fine, reseated all the other chips tested the cpu, checked voltages. i have been following the defender/defence command schematics both very similar but i notice the watchdog/reset input is different and it goes to a tied pin on an unmarked chip hence my shout out on here.

 

[mickyc22]

I've got a working one of those, what chips do you need to know about ?.

For circuit diagram, it should loosely follow early Defender, except for component locations.

At least the RAM is all socketed. Try re-seating all the socketed chips first.

pin 37 the reset from cpu tied to pin 16 and 17 on ic68 which is unmarked on mine
i assume its a 7411 going of other schematics but it shouldnt be a tied pin, hence im confused...

also ic 69 is unmarked

 

[philmurr]

I know it doesn't help you identify those chips, but is the reset actually causing you problems?

As it part boots that shows the reset and watchdog were working properly. I'd be inclined to check the EPROMs as the next step.

Then check the NVRAM, count240 signal and the vertical position counter



Edit: more information

 

[mickyc22]

I know it doesn't help you identify those chips, but is the reset actually causing you problems?

As it part boots that shows the reset and watchdog were working properly. I'd be inclined to check the EPROMs as the next step.

Then check the NVRAM, count240 signal and the vertical position counter



Edit: more information

im just trying to trace what is what, i agree the watchdog and reset are probably fine im just curious what those chips are, i've tested all the ram chips they are fine, swetted them out put them in a ram tester and socketed them back in, Im pretty sure the eproms are fine too as i get the 4 leds flash twice, correct me if im wrong dont they display a pattern if there is an eprom at fault?

 

[mickyc22]

I know it doesn't help you identify those chips, but is the reset actually causing you problems?

As it part boots that shows the reset and watchdog were working properly. I'd be inclined to check the EPROMs as the next step.

Then check the NVRAM, count240 signal and the vertical position counter



Edit: more information

count240 signal and the vertical position counter, could you give more details on this please bit beyond my knowledge

 

[philmurr]

count240 signal and the vertical position counter, could you give more details on this please bit beyond my knowledge

Download the Defender theory of operation https://www.robotron-2084.co.uk/manualsdefender.html

It mentions them both, you'll have to trace back which are the right chips on your board. But basically check that you can see them being selected (vertical position count is continuous but Count240 is just after the LEDs flash)

 

[mickyc22]

Download the Defender theory of operation https://www.robotron-2084.co.uk/manualsdefender.html

It mentions them both, you'll have to trace back which are the right chips on your board. But basically check that you can see them being selected (vertical position count is continuous but Count240 is just after the LEDs flash)

thanks been going through the theory manual not got as far as count240 will look into that

 

[cliff_poole]

 

[mickyc22]

Many thanks @cliff_poole I also got a pic from elsewhere that confirms the same as you what you have posted, not what i was expecting, im curious do you have chip in ic53 i dont but the person i got the pic off does im guessing his may be a different revision as also has few extra caps. i do belive this was a working board in the cab before it went into storage and i bought it

 

[cliff_poole]

Yours has a 7404 at IC54. I imagine they decided they could do away with the extra chip. Presumably it used to work so I doubt it will be the cause of any problems.
The missing caps have one end connected to ground, maybe they were added because of the different manufacturer of the chips, slightly different specs. Again, if it was working before ignore it for now.

Worth still checking the ROMs anyway, they may have bypassed the ROM check in code. Apologies if this is way too obvious, but is the board getting -5V and +12V.

 

[mickyc22]

i can confirm all the voltages are correct, so i have an eprom reader but not used it in anger, how do i check these roms is there a source for them anywhere? i assume this could be it https://wowroms.com/en/roms/mame-0.139u1/defense-command-defender-bootleg/3071.html

 

[Kingpin]

If you read the (E)PROM data you can verify the binary contents using MAME with the ROMIDENT command (for example mame.exe -romident romfile.bin).

 

[Dave2084]

Did you manage to get this running?

 

[mickyc22]

I didn't, I put this board aside and opted to put in a 19 in 1 locked into defender and spliced in a jamma connection, end of the day the cab was a bootleg/clone so dont think it matters. The original board and harness still in the cab, but myself im happy with it running the 19 in 1. plan to do away with the 4 way joystick put in a 2 way and add a thrust button.
how it was found

now with custom defender marquee

 

[Dave2084]

If you ever want to shift the PCB I collect Williams games and would love to add it to my collection.