MVS MV4 dead, solid light blue picture

[dragonpt]

Hi guys

So since my 1fz lost its sound due to an z80 error, i went and got my mv4 out of storage

Last time i used it was probably ~8y ago, it worked fine.

Now, all I get when trying to power it up, its an Solid light blue picture.

(Will post a picture later)

I've taken the upper board out, and with just the bottom board connected, same thing, just an solid light blue picture .

Went and check the current
( using an wall PSU 5v @8amp) , since the mv4 is +5v only modded

At the jamma pins ( with just the bottom board):
- getting +5.13 to +5.15 v
(this seems good)

- getting around 2.1 AMPs on the +5v jamma ( not sure of this is OK)


I've already recapped some of the bottom board caps with new ones , no change

No battery leak damage, since I took the original battery out when I got it ~9y ago

Checked DIP switch's , they all seem good, putting all of them ON, doesn't get to work ram test, just the same light blue picture

Any hints, to what I should check now?

Much appreciated, I would love to revive this board

 

[ack]

I would check for activity on the address/data pins of the cpu, to make sure its doing something. I would imagine it is or you would be getting the click of death. I would also check on the 2x 74LS273s near the palette ram to make sure their inputs and outputs look sane.

The diag bios + diag m1 will provide beep codes specifically for this case were the screen is jacked up, assuming sound is working on the board.

If you have credit leds, my updated version will also display the error code on them

GitHub - jwestfall69/neogeo-diag-bios: Disassembly of smkdan's Neo Geo Diagnostics BIOS with added features

Disassembly of smkdan's Neo Geo Diagnostics BIOS with added features - jwestfall69/neogeo-diag-bios

github.com

 

[dragonpt]

Thanks for the hints

Unfortunately I don't have diag bios nor a logic probe
( been trying to find an logic probe with audio beep for some time on eBay, recommendations???)

Just found out that with stock bios, I get the light blue screen only, as already described

https://imgur.com/HrelRip

BUT, using unibios 3.3 I get instead an black screen, BUT

Pressing START, 3 times and then down I can hear the MVS sound test: right, left , center just fine

( this doesn't work on stock bios )

So it is actually booting, just nothing on screen, I guess unibios allows to pass some issues...

Could it be the video RAM?

I know it can't be any cabling issue, as it works with 1 slots, and same cable worked with this 4th slot years ago

I know that's located at the bottom board, those 6 smd rams:

video ram
video ram
work ram
work ram
backup ram (lower)
backup ram (higher)

Thx


EDIT:

The 2x 74LS273s and palette RAM i suppose are this ones?

https://imgur.com/yotKfpl

 

[ack]

For logic probe I just have one of these

Elenco Electronics Lp-560 Logic Probe Electronics Testing Tool - Circuit Testers - Amazon.com

Elenco Electronics Lp-560 Logic Probe Electronics Testing Tool - Circuit Testers - Amazon.com

www.amazon.com

That is the palette ram and 273s I was referring to in your picture.

 

[dragonpt]

ok i've fixed it

using my super awesome finger on the video rams and pressing them would cause the screen to show some few artifacts on the corners

went ahead and replaced the uper video ram, mv4 finnaly show picture . but the text was corrupted
replaced the lower video ram, and now its awesome, working great , good quality picture, zero artifacts

i used SONY CXK58257AM-10L (taken from a broken 1fz), instead of the stock SONY CXK58256MM-12 their datasheet seems the same, i think it's fine.

just so happy to have my baby working again

https://imgur.com/zwis424

https://imgur.com/bCKlgp4

https://imgur.com/YbnHdto

thx for the help i also reflow the 273s just in case.
waiting for a logic probe that i order, this will help a lot in the future

there's some ebays sellers that sell DIAG bios, i'll probably buy one when my paycheck comes

cheers