Dead MV1F slot, Black screen, watchdog, wram, no audio [SOLVED / ICs swapp & trace repair]

[Retro Mecano]

Hi again,

I recently had an MV1F slot (the one with the two controller ports) that wouldn't boot.
Basically, when powered on, the red LED wouldn't light up, and the monitor switched the signal to a black screen.
No reset, no watchdog, no click, no sound, absolutely nothing.

I measured a few points on the PCB and there was definitely 5V flowing.

I changed the BIOS to UniBios 4 and Diag, without success.

I spotted a few damaged traces around the battery, so I patched the traces and cleaned up the residue. I even changed the 32k crystal on the other end of the board.

So what should I do? This is the first time I've seen a slot whose LED doesn't light up.

 

[ack]

Sounds like you have hard dip #8 in the 'on' position. When its 'on' it will cause the board to go into a pause state. If enable at power-on you get a black screen.

 

[Retro Mecano]

Sounds like you have hard dip #8 in the 'on' position. When its 'on' it will cause the board to go into a pause state. If enable at power-on you get a black screen.

Checked that already, it'on off position. Could it be some IC controlling rhe DIPs?

Still wired that the LED doesn't lighten up..

 

[ack]

Its possible, but I missed the bit where you said you tried with the diag bios. It wouldn't care if that dip is on.

By chance is J2 solder jumper near the NEO-B1 chip jumped?

 

[Retro Mecano]

Its possible, but I missed the bit where you said you tried with the diag bios. It wouldn't care if that dip is on.

By chance is J2 solder jumper near the NEO-B1 chip jumped?

No J2 is open.
Few pics anyway for it's status.
i made the jumper wires after battery leakage
The 2 ICs 5863 seem wierd to me though..they are different.

 

[Retro Mecano]

Its possible, but I missed the bit where you said you tried with the diag bios. It wouldn't care if that dip is on.

By chance is J2 solder jumper near the NEO-B1 chip jumped?

UPDATE

Following up some old youtube repair videos, i found out that black screen could be from missing clock signal to CPU. And guess which IC handles it... again it's the Neo-D0!

In privious thread it caused missing sound on the MV1Ax dlot.

So i swapped it, and now the slot boots to a watchdog. At least it's alive now i can try to learn how to use a probe..

 

[Retro Mecano]

Made few replacement after NeoD0, including NeoF0 and NeoEo which were getting hot.

But still watchchdog. Next went to WRAM area and couldn't see activity on WE/OE pins on both RAMs. Schematics say it is handled by NeoC1, so i went tghrough and replaced it (it was getting hot also)

I am still a beginner using probe and don't know how to read it properly, but here is what i found now:

RAM @H4:
Pin20: green (low?)
Pin22: yellow flashing(pulsing?)
Pin27: yellow flashing(pulsing?)

RAM@H5:
Pin20: green (low?)
Pin22: yellow flashing(pulsing?)
Pin27: green (low?)

Activity is different on pin27, although i thought they were accessed in parallel.

Can you explain the readings? Does it mean the new C1 is toast too?

 

[Retro Mecano]

@ack any idea how to proceed for this update? Thanks in advance.

 

[ack]

I would check connectivity between the CPU and the bios chip. Honestly that board looks pretty bad with all the rusted pins and corroded traces.

 

[Retro Mecano]

I would check connectivity between the CPU and the bios chip. Honestly that board looks pretty bad with all the rusted pins and corroded traces.

Checked all the traces and patched the few suspected.. Anyways, now just by flexing a little the board i Managed to get the following error with diag bios:

 

[Retro Mecano]

Checked all the traces and patched the few suspected.. Anyways, now just by flexing a little the board i Managed to get the following error with diag bios:

UPDATE

Thanks to the Ram location templates on ack's github, i could focus cheking traces on the lower wram. Finding them all fine, i went straight to swapp it, and finally i could see the sweet "test pass" from diag.

Now the slot is able to play games on Unibios, but without sound.

Diag bios gives following error:

I'am almost there.... your help will be appreciated.

 

[ack]

its almost right, so might just be 2 bad data line traces. I would check SD0-SD7 to the Z80 and D8-D15 to the 68K on the NEO-C1. They might not be a direct connection, I dont recall.

 

[Retro Mecano]

its almost right, so might just be 2 bad data line traces. I would check SD0-SD7 to the Z80 and D8-D15 to the 68K on the NEO-C1. They might not be a direct connection, I dont recall.

Ahh the sweet sound of the Diag cart test pass... "prrrrrrrrrt". Bull's eye @ack

It was defenetly two vias connecting SD1 & SD2 from NeoC1 to RAM6116 to Z80. Connection was actually to the ram, but 2 vias were not making it to z80, knowing that i repaired the whole corroded area before.

Great advice @ack thanks a lot my friend for pointing out the exact area. That spared me whole audio section multimeter testing.

Now it would be silly to ask why the LED is not lighting up, even i changed it .
Nah i will figure that out later..

 

[Retro Mecano]

A quick recap on the whole repair done, ot might be useful for others.

Black screen:
NEO-D0 (swap)
Traces repair near it (battery leak)

Watchdog:
NEO-E0 (corroded pads/getting hot/swap)
NEO-F0 (corroded pads/getting hot/swap)
NEO-C1 (corroded pads/getting hot/swap)
BIOS SOCKET (Weak contact pins/socket swap)

WRAM Error:
WRAM Lower (swap)
Hc32&HC04 (corroded pads / socket inserted)

Garbeled graphics:
2K VRAM (corroded pads / wrong chip ref from previous owner, RAM swapped / socket inserted)
Palette RAM (corroded pads / socket inserted)
trace repair

No audio:
RAM 6116 (corroded / swapped / socket inserted / vias repair under chip)

No LED light
Swapped still no light lol (have no clue )

Thanks all for supporting in this very long repair.