vg 8235 /19 black screen

Resident (45)

29-01-2018, 21:23

my vg 8235 has black screen
i open first time all ak after one reboot black screen
after 5 reboots something on screen as invalid instruction and after that black screen
replaced z80 (i socketed time ago) with new working one
tried rams if become hot is all ok
i think to recap all electrolytics
psu recapped 2 months ago and all voltages is ok 12 -12 5

but black screen ,any ideas what to do next

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By Grauw

Ascended (10768)

29-01-2018, 21:31

Could be that one of the ROMs has bitrotted.

By Wierzbowsky

Guardian (3606)

29-01-2018, 21:34

Or RAM on the 2 last pages is unstable.

By Grauw

Ascended (10768)

29-01-2018, 21:44

I think the RAM chips are the same as the VRAM chips? (81646) If so, could try swapping them to see if that’s where the problem lies… bad video RAM chips do not prevent the MSX from booting, bad RAM chips do. Also, if the bad RAM is used for video output, it’s fairly easy to diagnose from a picture which of them went bad.

RAM issues are definitely more common than ROM issues, so it’s one of the first suspects. After RAM, logic ICs I think, and caps. VDP / Z80 don’t break down very often judging by reports I’m reading here.

By subzero79

Resident (45)

29-01-2018, 21:48

im awaiting for new 4464 ram chips for replace i will soket all ram replace with new and test chips after one to one,
rom is ok burn new set with my programmer and compare old ics all ok

By subzero79

Resident (45)

05-02-2018, 18:46

4464 chips replaced
ls chips replaced
z80 replaced
reset clock present still black screen
i think rtc

By Grauw

Ascended (10768)

05-02-2018, 19:06

Yeah, I’ve heard about the RTC causing this symptom before. It wasn’t even a malfunction, just certain bad data which can block the MSX from booting like this. Did you disconnect the battery?

By maxis

Champion (512)

05-02-2018, 19:39

@subzero79
Try to put MSX1 BIOS instead of MSX2 main ROM. If the problem is in RTC, the machine will boot.
Start it with SHIFT, since the mapper will not be initialized and DISK ROM initialization will crash it.
If you will put CX5MII main BIOS it's even better, since it will initialize the mapper correctly, but will be still using MSX1 hardware. Then you can use the disk drive and run some diagnostic utilities from floppy.

By Leonardo Padial

Expert (73)

05-02-2018, 19:48

Think this MSX have EPROMs memories.
The code in EPROM have one time over 20 years garantie.
One sigle bit desprogramed is enoug for change one DATA or OPCODE. This can put black the MSX
If you think the problem is your EPROM, I can reprogram your EPROM if you send me the .ROM

By subzero79

Resident (45)

06-02-2018, 11:24

thanks i have programer and equipement
motherboard travels to france to mr jipe

By Hans41

Expert (71)

25-02-2018, 19:46

Folks,

I'm afraid I ruined a Flips VG-8235/20.

Followed the instructions Bas has on his site. Replaced the eprom with an 8245 60hz one I got of Markplaats quite a while ago. Altered the cable to use a pc drive. I had soldered the drive to be an a-drive some time ago already. Fired it up, looked fine. MSX logo, memory amounts, etc. Did not get into basic/disk basic though. Stayed on a blue screen. If I remember correctly, the drive didn't do a thing.

Second time I booted it, black screen. And the machine immediately switches to capitals and lights up the corresponding CAPS led. Sometimes a white screen after a reset, but in general nothing. Conclusion: I've messed (it) up somehow.

I've tried the original eprom, same thing. I've tried a memory mapper, same thing.

Do you guys have some suggestions that I can try with my limited knowledge to somehow get this machine working again ? I have converted drives/cables on a few nms-8245's and one vg-8235/00 (successfully).

TIA.