Johns-Arcade

Are you sure it's not a KZ-20?

Exact same one's I've used as replacements in Dragon's Lair cabs. Regards, Johns-Arcade.

Funny, I don't recall selling you a monitor, it fact, I don't recall the last time I sold anyone a monitor. Maybe you mean a certain person whom for some reason just loves to use my business name? I dare say I could come up with 80 reasons why, but best not to go there! :D If you're on the Gold Coast, drop @TrevorP a PM and he might be able to sort you out. Regards, Johns-Arcade.

I'm assuming you need one to run a CRT monitor? Also, where in Qld are you? Regards, Johns-Arcade.

It's fine, don't worry about it. Regards, Johns-Arcade.

I also own a Q*bert, but I'm not really interested in the other games available on the kit. I've also heard they can be problematic and easily damaged, hence why I removed it during this repair (and to rule it out as a possible problem) I think this board would be a better buy. http://www.arcadeshop.com/i/1060/mylstar-jamma-pcb.htm Regards, Johns-Arcade.

I thought I post this up for future reference, just in case it helps in the future. I don't normally document my repairs, as I usually can't be bothered, and even with this repair I omitted to take a few pictures explaining what's going on (CRO shots). This is an original dedicated Gottlieb Q*bert that also happens to have a multi-kit fitted. Although the game was running, the foreground graphics were either missing or made up of lines across the screen. First job was to remove the multi-kit and return the board to its original condition. This would allow access to the board for probing, and also rule out the multi-kit as part of the problem. I also didn't want to risk damaging the kit during any repair. With a new set of Roms burnt and fitted, the game still displayed the same fault, so the kit was assumed to be ok. I didn't want to go to the effort of building a test harness for this game, so I positioned the cab as close to my test bench as possible. I still needed to hook up another monitor so I could see what was happening on the screen. I also had to make an extension cable from the cab to the extra monitor, but it was still quicker than making a complete test harness. The fault was with the foreground graphics, so I grabbed the board schematics and started probing that section of the PCB. I checked all the usuals suspects with my logic probe, but everything seemed to look ok. Normally with a board on the bench I use my CRO over a logic probe, but as I was working in the back of a cab, trying to see what was happening on the CRO was near impossible with my crappy eyes now, so the logic probe was easier to use. After everything else seemed ok, I then concentrated of the line position Ram and line object Ram where I suspected the problem lay. In total, there are 10 x 74s189 Ram chips all sharing the same address bus. The major issue with any IC on a shared address or data bus, is that a fault on any IC is very hard to see, and basically impossible with a logic probe. All these Ram are addressed via a 74157 (Quad 2-Line to 1-Line Data Selectors/Multiplexers). As mentioned, I suspected the fault lay in this part of the board, but the outputs on the 74157 looked to be pulsing nicely on my logic probe. I decided to test this anyway by temporarily shorting the address lines to each other. Doing this brought up some of the missing foreground on the screen so I suspected the 74157 wasn't driving the Ram as expected. I then hooked up the CRO which showed that the output on pin 7 wasn't quite right. This is a prime example of where a logic probe has its limitations with these kind of faults. I removed the IC and decided to test it on my Wellon programmer. Even under test, it passed. I also decided to try it on my cheap crappy Chinese tester. Again the IC passed. Even though the IC passed both test, I wasn't happy with the output on the CRO, so a new IC was fitted to the board. This fixed the fault, and the game displayed all graphics correctly. The Q*bert multi-kit was reinstalled and is working great. So why did the IC pass testing? Basically the output is unable to drive all the Ram in circuit, but on its own no problem, so it passes test. To be honest, I never rely on any IC tester for this very reason. If I suspect an IC is faulty and I remove it from the board, I always fit a new one. Regards, Johns-Arcade.

Replace and socket all the IC's in the vector output section Mark, makes it a lot easier in the future. Looking at the image it doesn't look like a DAC issue to me. Regards, Johns-Arcade.

Are they driving past Hitler in that shot? :017:

Remove the chassis and send it to Joey @Jomac Regardless of the fault, I think it best you let an expert take care of it. Regards, Johns-Arcade.

I've been warning people about this guy since the old RGVAC days. Why people continue to associate with this guy is beyond me.

Give joey a call.

What happened to the one in the chassis?

Well you sure gave me a good laugh imaging that Rat :lol

I have boards, but no idea if they are working (most likely not).

Until you swap one of the wires from the vertical windings with one of the wires from the horizontal windings, then the fun comes to a sudden stop.

Does it need to be working? And yes, it's non-Jamma. Regards, Johns-Arcade.

It's corrosion. The reason it's green is because it's copper.

I'm just saying, if you don't want people making remarks about your offer, take it to PM.

A low ball via PM would have been a better option.

Maybe suggest Kev, but he won't be cheap either.

Kev maybe (KFE)? :unsure The biggest issue with these clone boards is to be able to work on the PCB, you first need to make a harness to be able to plug the thing in. That's an hour+ operation in itself. You then need to fault find the issue, repair it, and you're now talking possibly many hours in labour. I personally think it's un-economical to repair these PCB's myself, or overly expensive to try (and the owner obviously doesn't want to pay). He's do better finding someone to convert it to an LCD and sticking a 60 in 1 board in it.

And this is the new world we live in :rolleyes Funny how I would wander the streets as a kid with my BB gun and no one batted an eyelid, or the kids in army cadets with their 303's flung over their shoulder waiting at Blacktown railway station of an afternoon, again, no one concerned. Now pink, blue or polka dot (insert any colour) guns on video games are considered illegal. How could this stupidity be allowed to happen FFS?

Are any fuses blown? Regards, Johns-Arcade.