Garbled graphics on G7200

[HubertF]

Hi all,

I'm new in town and directly have a question -- I tried searching the forums, but to no avail; maybe I just entered the wrong keywords.

Anyway: I'm trying to revive a G7200, but after inserting a module and powering on, it just shows garbled graphics. The patterns seem to be random, and sometimes I get no picture at all.

I checked the PCB for cracks and bad solder points, but after all these years, everything looks perfect. I swapped the CPU, Video Chip and RAM from a functioning G7400, but no luck -- still the same garbled junk on screen.

I got "Super Cobra" up and running one time, so all in all, everything seems to be working, but there's obviously something wrong anyway. I cleaned the module port with a toothbrush and IPA, but still didn't succeed.

So, before I grab the technical manual and the Osc, I'd like to know if anybody here maybe experienced similar problems and can lead me in the right direction? Like I said before, Super Cobra started up once, but I didn't have any luck in repeating that.

Do you think it's a mere mechanical problem? A faulty logic chip, maybe? I'm lost at this moment, since the console obiously works, but somehow fails to initialize properly after a power on.

Any thoughts, ideas & hints are very welcome!!

Thanks in advance,

--H

[manopac]

sounds to me still like a problem in cartridge connection and you got lucky one time ... did you clean the contacts on the cartridge properly, too? and maybe its easier to first get another cartridge and try with that instead of searching for the fault in the G7200

good luck fixing it :-)

[HubertF]

Thanks for your reply, but believe me, I tried 20 cartridges or so, but only got lucky this one time with Super Cobra.....hmpf. (Fun fact: they all work flawlessly with the G7400.)

Anyway, I believe you're right, and there still is a problem with the module port. I guess I'll reflow the solder points and clean that thing thoroughly again......

I'll keep you posted. 

[HubertF]

Hello everyone, here's some exciting news (at least for me):

It's not a mechanical problem at all.......it's the CPU gone mad! I managed to get a friend (who also owns a G7200) to swap CPUs, and with his CPU in my G7200, it works flawlessly. On the other hand, with my CPU inserted in his G7200, it shows the exact same symptoms, e.g. garbled graphics, no sound, etc. Anyway, I still can't tell why I got Super Cobra to run on my (defective) G7200!? But I don't care anymore, since it's offical now, my G7200's CPU is -- at least -- partially fried.

So, what are my options here? As far as I can tell, I can't just insert an 8048 CPU from eBay, since it doesn't have the "BIOS", is that correct? BUT!! Looking at the G7200 schematics / BOM, I noticed there's a 82S129 chip on board, marked as "ROM".

Question 1: could it be the G7200 has a "stock" 8048 CPU on board?

If the answer is "Yes!", my problem's solved, since stock 8048 can still be obtained at a reasonable price on eBay. Anyway, if it's a "No!", this leads to

Question 2: I have a 8748 CPU at hand, which is the EPROM version of the 8048.....but I have absolutely no means to program this 40+ years old bitch! I do own a programmer, but it's "to modern" and can't handle the 8748, which needs (I think) 21Vpp. And here's the question:

Is anybody -- preferably from Germany or EU -- willing to program that chip for me? I'll cover all expenses, of course! (I know there's a project for building an Arduino-based programmer out there, but since this is a one-time job, building the device seems a bit of an overkill to me....!)

I'd appreciate hearing from you, whoever you may be......

Thanks in advance for your answers.

--H

[Xuul]

I found this:

https://videopac.nl/forum/index.php?topic=2859.msg28174#msg28174

[HubertF]

Yeah, I found/read that, too........anyway, the issue's solved, I managed to get a D8748 (NOS) programmed with the O2 BIOS, and now the G7200 is back alive without any problems.

Hooray!!

--H

[Xuul]

Nice, congrats