Mega Force PCB?

[big10p]

I bought this faulty Star Force board on a whim as it was cheapish and thought it would be a good start to learn a bit more about board repair, as I have a working board to compare things with.

However, this one is different to my working board, which is 3 layer. This is 2 layer. Number on it is 5904v2. Pulled all ROMs as there's some corrosion (caps are shot). Tried romident on a couple but results were inconclusive.

Can someone definitively ID it? Think it's Mega Force (US version of Star Force), but not sure. 🤔

 

[sukhbir]

Yep it's a copy of starforce, it was licensed by tecmo and genuine board and I don't think it uses the encrypted cpu.
All is needed to is put in starforce roms,which ones I'm not sure.
That 2 boardset is identical to the bootleg starforce pcb.

 

[big10p]

Yep it's a copy of starforce, it was licensed by tecmo and genuine board and I don't think it uses the encrypted cpu.
All is needed to is put in starforce roms,which ones I'm not sure.
That 2 boardset is identical to the bootleg starforce pcb.

Thanks! That's what confused me. One on eBay that claims to be genuine, and another I saw while googling saying it's a bootleg.

 

[favouredson]

That is genuine and is simply a condensed version of the hardware with all the unnecessary bits removed.
The same boardset was used for Baluba-louk no Densetsu.

Also, the bootleg I had years back was a three layer set the same as the more common Star Force boards.

 

[sukhbir]

There's a two layer as well but hard to come by.

 

[big10p]

That is genuine and is simply a condensed version of the hardware with all the unnecessary bits removed.
The same boardset was used for Baluba-louk no Densetsu.

Also, the bootleg I had years back was a three layer set the same as the more common Star Force boards.

Interesting! Does that mean I could get Baluba-louk running on this just by doing a ROM swap, or is there more involved? Great game, so that would be very tempting, as I already have a Star Force.

 

[favouredson]

With the two board set it is just a straight ROM swap.
I had Baluba-louk running on my old three board bootleg but I had to split some of the ROMs.

 

[big10p]

I'm back to trying to get some sign of life from this board, having now replaced all electrolytic caps and fitted a load of new sockets.

Initial power up and it's dead. Z80 constantly resetting and clock pin stuck low.

I want to check the crystal clock with my scope but read not hook up directly to the crystal oscillator, but somewhere after output has been buffered?

Can't find schem for this board, but clock seems to go to pin one of an ls367 which is Disabled A (whatever that is). Do I hook the scope to an output pin of this? Which one?

Out of my depth here. Lol

 

[Jacmar]

You can directly probe the legs of the crystal .. I've never had an issue doing that. if crystal is oscillating just follow the path until it you find the reason it doesn't get to the cpu

 

[big10p]

You can directly probe the legs of the crystal .. I've never had an issue doing that. if crystal is oscillating just follow the path until it you find the reason it doesn't get to the cpu

Ok, I'll give that a go. I might try tracing backwards from the CPU too, to see if that gives me any clues. Thanks.

 

[big10p]

I've just got a SLICE so I'll give it a go on the ls367, too. Not sure I'll be able to decode what it tells me, though. Lol

 

[big10p]

Ok, the crystal seems to be dead, according to the logic probe. Should I be able to read a voltage between the two crystal leads?

 

[Jacmar]

Logic probes aren't ideal for checking clock signals. You should use your scope probe on the crystal legs. you are looking for a signal like this ....



This is a 16Mhz frequency waveform (measured in the bottom corner of the scope display) ... you are looking for a frequency that matches what is printed on your crystal

 

[big10p]

Logic probes aren't ideal for checking clock signals. You should use your scope probe on the crystal legs. you are looking for a signal like this ....

View attachment 52943

This is a 16Mhz frequency waveform (measured in the bottom corner of the scope display) ... you are looking for a frequency that matches what is printed on your crystal

I'll try using my scope tomorrow, but I can usually verify the clock is at least active using the logic probe, but I'm getting nothing on this one.

 

[Georgian2]

Without schematics it is easier to trace to clock signal from the CPU backwards.

 

[big10p]

Without schematics it is easier to trace to clock signal from the CPU backwards.

CPU clock pin goes to a pull-up resistor and into pin 3 of the same ls367 the crystal is connected to.

I read about 95mv between the crystal leads on another game board, but I'm getting nothing on the crystal on this board.

 

[Georgian2]

And the ls367 is not pulsing on the outputs? The signal on crystal is low, many logic probes won't pick it up.

 

[big10p]

And the ls367 is not pulsing on the outputs? The signal on crystal is low, many logic probes won't pick it up.

The ls367 is getting 5v but doesn't seem to be doing anything. I'll try probing it with my scope tomorrow. I'm also going to hook it up to SLICE.

I'm new to this stuff so I'm not sure if a faulty component connected to the ls367 is stopping it from working. Looks like it is also connected to a couple of ls74s which I read are often used to buffer clock signals? Feel like I'm heading down a rabbit hole. Haha.

 

[Georgian2]

If you are lazy on desoldering, you can snip the outp pins in the middle so that the outputs are separated from the other ICs. If the outputs are still pulsing, some inpout connected to it, is stuck low or high

 

[sukhbir]

Ok, the crystal seems to be dead, according to the logic probe. Should I be able to read a voltage between the two crystal leads?

Logic probes are used for TTL or cmos level ,the crystals frequency is analogue so best to use an oscilloscope.
very rare a crystal fails from my experience,there should be 2 ceramic capacitors close to the crystal which sets the crystal to oscillate check they are not broken.