vg 8235 /19 black screen

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By zett

Hero (608)

zett's picture

25-02-2018, 20:09

check fuses

By Philip

Champion (380)

Philip's picture

25-02-2018, 22:58

And does it work without diskdrive ?
And doublecheck the two wires that were soldered on the motherboard...

Otherwise the usual checks, voltages, starting a cartridge which produces sound without interaction, etc.

By Hans41

Expert (71)

Hans41's picture

25-02-2018, 23:51

Thank you for your suggestions !

Please correct me if I'm wrong, but there's only one fuse near the L1 elco that I had to replace with a wire ?
Or are there more ? I checked that fuse, was ok.

I've disconnected the diskdrive already. Doesn't make a difference, sadly.

I did try a cartridge (Car Jamboree), that didn't work.

Does a loud click (switching on the CAPS) mean/indicate anything ?

Although I didn't hear (besides the CAPS switching on), see or smell anything, I did find a small bit of goo/plastic (lying on the motherboard) near TP13/C25. Could of course have been there before, only started to look at the mb closely after the MSX stopped working. Maybe, I've fried the pcb with the monitor and printer connections ? Can take one from one of my 8235/00's, but run the risk of those getting damaged as well. Bummer.

Good suggestion to check the wires on the underside of the mb, but I kinda wanted to check that as a last resort, cause it would mean taking the mb out again. If nothing else fixes things, I shall absolutely have to. And the MSX booted once, shouldn't that indicate they were (and hopefully still are) connected ?

By the way, I have a jumper (connecting 1-2) next to the diskrom, not a cable like shown in Bas' instructions.

By Philip

Champion (380)

Philip's picture

26-02-2018, 14:23

The click is it the motor relais or the caps ?
And can you post a picture of the goo/plastic ?

Did you check the voltages ?

The jumper seems normal looking at some naked vg8235/20 pics on the internet Smile

By Hans41

Expert (71)

Hans41's picture

27-02-2018, 13:04

I couldn't tell the difference between the clicks, to be honest.

But, it sounds like the click you'll hear when you start H.E.R.O.
But, that always results in CAPS on AND Motor On, if I'm not mistaken ?

I've removed the small piece of goo/plastic already. It did leave a small stain on the motherboard, so I assume it was at least warm, maybe even hot. Again, when that happened, I don't know. May have been there before.

In the WIKI section, the picture of the jumper next to the diskrom indeed looks the same as the mb of my 8235/20.
I assume the cable in Bas' pictures doesn't make a difference when it comes to the modification(s). That would make it a different vg-8235/xx.

I have not yet checked the voltages. Is there a checklist of some sorts ?

Again, thank you for your suggestions. Cool

By Philip

Champion (380)

Philip's picture

27-02-2018, 19:56

Well, I think the click means the bios is not being started. At least a 8250 does this when you remove the bios. Also it does this when I installed a 7mhz kit and managed to damage one of the address lines when removing the cpu (and I did cut out the cpu and I was really carefull...) Anyway I managed to find it using a logic probe as there was no activity on this address line on the roms.

So probably the only easy thing left to check is if the voltages (5V, 12V and -12V) are correct. These can be measured on the cardridge slot for instance.

Otherwise you will need to use a logic probe or scope to check if all the relevant signals (clock, interrupts, address lines etc etc are working) Just read some of the black screen topics in this forum.

Or you can just check if the wires on the bottom got loose Hannibal

By Hans41

Expert (71)

Hans41's picture

04-03-2018, 22:01

Philip, thank you.

I connected a pc diskdrive connector to the MSX power cord and connected both ground wires to line 11. Ouch.
Did the (pc) drive because of that get 12v as well, and that caused probs with my vg-8235/20 ?

Is it possible I messed up the 12v circuit ?

Have checked the power connector from power supply to mb and it gives me 5.12v on red and black and 12.15v on yellow and black, so no probs there.

When I have the motivation to pull out the mb and check the wires, I shall. Right now, I don't. Maybe tomorrow.

Still, when modifying a vg-8235/00, you have to disconnect two lines on the mb and solder two (new) wired ones. On the /20, you only have to solder two wires and disconnect no lines.

By Hans41

Expert (71)

Hans41's picture

16-03-2018, 22:17

The new rom I used, works in a vg-8235/00, so I assumed it wouldn't work in a vg-8235/20, since the /00 is a three rom machine and the /20 a single rom machine. Long story short, I ordered a new rom from Bas to be sure.
Plugged it in...yay, MSX logo, memory amounts, etc. But, no basic screen. I switched the machine off.

That was like earlier experiences, so I feared what was to come next.

Switched it back on. Yes, black screen again. Sad

I am glad that the MSX gives me some encouragement, but if I'm killing the eproms, it's going to get expensive. Next to that, I haven't found the reason for it not functioning properly.

By Grauw

Ascended (10685)

Grauw's picture

16-03-2018, 22:23

Are you sure it’s not the RTC? Disconnect the battery so it always resets after being off for a while…

Since the EPROM does work fine for a while, and it shouldn’t just die like that I think.

By Hans41

Expert (71)

Hans41's picture

16-03-2018, 22:37

Grauw, thank you for your suggestion.

Do I have to cut the wires to the battery or is there a more civil method ?

Also have to be careful with discharges, cause with this weather and dry air it's lightning all over the place.

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