Space Battle - Transformer Question

[biglouie]

Not really "repaired" boards per se Lurch!!

Ive got lucky with some easy fixes on a couple, the rest I just learn stuff and fail. a lot.

 

[PaulSwan]

Re: The AC voltages

One option is to temporarily strap-bypass the +5V and +12V to the edge connector and then you can build a JAMMA adaptor to bench test it. There should be some guidance documented on the web for Galaxian AC to DC conversion.

 

[biglouie]

I'll have a look around. I've watched many many Galaxian repair videos these last few days. in the hope that something in there makes me think of something on this board

Off to storage to find a z80a in the morning.

Anyone near Sevenoaks? Hah

 

[biglouie]

EPROM 1 is different to the others. Fujitsu. Not really famed for their reliability.

I can read it. As a 2716. All the other EPROMs are that.

What i dont know, as this code doesnt exiist in mame, is if its corrupt or not.

Few FFs in there!

biglouie2021-12-28 10:12:24

 

[philmurr]

That code looks fine, including the FFs

 

[biglouie]

Thanks Phil.

Tried a D780c from Galaga. No change, but as mentioned Space Battle is D780c-1 so a quicker chip.

 

[favouredson]

EPROM 1 is different to the others. Fujitsu. Not really famed for their reliability.

Fujitsu EPROMs are no less reliable than others. I have programmed many MB8516s and have rarely had any issues with them.

You're probably thinking of TTL ICs.

I can read it. As a 2716.

That's because it is a 2716. Not all manufacturers played by the same rules back then...

 

[biglouie]

I
had a look at the status of the pins on the LS74138's that feed the ROMs. There are two:

I suspect this enables the ROMs for reading.

1,2,3 are Inputs

4,5,6 enables (4,5 being active lo)

8 is GND

7,9,10,11,12,13,14,15 are outputs

16 is 5v

Results are below. What I need to understand, is what I should be seeing and what these things actually do. I was looking at the truth table, but it has things as H or L. What if its pulsing and showing both H and L on the probe? Is that both high and low and data moving? I think I need to watch some youtube about truth tables.

Seems to me, if Pin18 is ENABLE low on the EPROMs, and thats decided by the outputs of these 138s, then they are never getting enabled?

biglouie2021-12-29 14:18:22

 

[Lurch666]

If the software in the roms isn't running properly then the only the code in the 1st rom (1K) will be running and you are seeing activity on pin 15 of 6J.

The addressing system will not enable another eprom until the program code runs successfully. I notice you are seeing activity on pin 13 as well but that could just be a symptom of the code not running correctly.

 

[biglouie]

Sometimes the logic probe flashes both HI & LO and the pulsing light is on/off. Sometimes its just LO is lit, but pulsing light is going... How can it be both Hi & LO, or is it Hi & LO so quickly?

Interesting re the above on 1K.