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Any advice on where to start with this dead MK1 bootleg?

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Glen(CRG)

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I recently purchased a bootleg MK1 board from eBay, granted this was sold a faulty for spare and repairs but I've fixed plenty of retro computers and consoles before so I thought I'd take up the challenge (plus it was fairly cheap).

DSC_1175.jpg


But its very dead. I gave it a quick clean checked for shorts but all it does is produce a static screen which either looks like the below or it'll be the same as the bottom half just over all of the screen. Its always a static image.

DSC_1176.JPG


I've checked for power around the board and its all there, well 5V reads 4.9 but I'm sure that's ok. There appears to be clocks present on my logic probe, I don't have a scope that can read anything above a few mhz, and the reset line looks good to the CPU. I've went looking for schematics but since this is a bootleg I don't expect to find them.

I haven't spent much time with it yet but the other thing I want to look at is the ROMs. If I dump these does anyone know of a matching rom set anywhere I can compare against?

Or would anyone by chance have seen a fault similar to this and be able to guide as to where to start looking?

I don't have a lot of experience (none really) working on arcade boards so any advice would be appreciated.
 
Haha, I think we have bootleg MK1 twins - mine is in (only very slightly) better shape than yours, it boots and plays fine for a few minutes before slowly developing more and more glitchy sprites and then eventually nothing. Leave it alone for for 30 mins and the cycle can repeat.

Bootlegs are both super simple (because they use lots of standard chips instead of weird IC's) and super complex (because there is absolutely no Information on them available).

Sadly I don't have a device capable of dumping the ROMS off mine, but its been on my list to buy for a while now.

Will dig my one out of storage and post some photos to see if they are truly identical
 
I'm going to try and dump the roms this evening but as there is no marking on them to suggest what they are could anyone help identify the chips?

rom1.jpg
rom 2.jpg
rom 3.jpg


The only thing I have to identify them is the silk screen. The 3 roms in the first image are noted as 2M, the 2 roms in the second image are labelled as 4M. I assume this is 2 megabit and 4 megabit? The 3 chips in the 3rd image I assume are roms but there is nothing to identify them. I also note there is some damage to the PCB close to these 3. I'll need to clean all this up later to be sure nothing is broken.

Any advice would be appreciated.
 
Does your programmer have the ability to auto detect the chips? Maybe try reading the M1 chips as 1 megabit eeproms.

A scope will help or at least a logic probe. The graphical glitches are usually related to video ram error or related logic chips.
 
SB_Electronics said:
Does your programmer have the ability to auto detect the chips? Maybe try reading the M1 chips as 1 megabit eeproms.

A scope will help or at least a logic probe. The graphical glitches are usually related to video ram error or related logic chips.
Click to expand...
Unfortunately my programmer, tl866 can autodetect, or certainly not to the best of my knowledge anyway.

I have tested the 2 6264 ram chips from it in the same programmer and they are both faulty. Although I'm not sure I trust its ability to test as it's lead me astray before with logic ic's
 
I've had a discussion on another place (discord) and the opinion of 2 folk anyway is that my 5v rail is too low potentially causing the issues on this board. Initially I was only getting about 4.93v which sparked the conversation. After some cleaning of the jamma edge connector I've got it up to 5.02 at the edge connector dropping to about 4.99 at the far end of the board (on the top board so maybe loosing a bit through its connector too). Still loosing a bit from the supergun which sits at 5.06v but to my mind those numbers should be fine.

Granted my mini supergun isn't exactly the best, its an aliexpress special but I'd rather not be spending £100 on new gear until I know for certain that its a problem. Its not that I don't trust said people who said this, in fact one in particular I would take his advice but just looking another opinion. As I said I'm new to arcade stuff but certainly in vintage computers or consoles I wouldn't see 4.9off volts as an issue.

Given that I do know there are faults on the board in the form of those 6264's (new ones have been ordered) I'm not convinced about the voltage thing being an issue. The consensus in said other place was you need to drive the 5v rail to 5.1v. With my current setup I can't tweak it. You get what you get. I should note that it drives my MVS and another bootleg board I have fine.
 
I agree, a low voltage <4.95V could cause issues with some picky boards but 4.99V should be fine. The reason people recommend 5.1-2V is to compensate for any voltage drop. As you said, don’t rush to buy expensive equipment until you rule out the cheaper causes. Have you recapped this board?
 
I haven't recapped it as yet, although there aren't a lot of caps on it. I also still need to remove the battery as I found another thread about this board suggesting the dead battery may stop it from booting.
 
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