*Solved*Pce-duo Picture fades out and freezes. Then comes back if witched off.

[NichlasEk]

Edit2: it was ic 905 (HSRM20256LM12)
I found on console 5 that snes part CXK58257AM-SRAM
Is the same part. I swapped ic 905 first and got even worse graphic.
I then swapped over ic904 to and got words back on the screen but still garbled.
So i left the snes ram at ic904 and put the hsrm from 904 at 905 and presto!

Think il buy a couple of beer for the weekend to celebrate!
Thanks guys!

PS got the new laser up and running on the other duo to.
Game on!

Edit1:

I took a toothbrush to the board and cleand all the chips with isoprop. Then i touched up all dull looking solderjoints and vias i could find.

Now i get a nice picture (perfect coulors) with stable sync, but with strange sprite corruption.
Where to search next? RAM error? missing continuity between chips? But where?

I have Atatched a picture of the problem, it does however look different in every game. Vigilanty plays almost fine: "https://i.imgsafe.org/fd1248fc37.jpg"

Hi!

I recently got two broken pc engine duos. Got one of them back after recap and mending a couple of vias.

The other one had sync issues and grapich issues from start. It did play hucards with minimal graphical distortions. I did a recap and a clean. No vissible corrotion on the board.
Now however, when i turn it on iget perfect rgb picture and then the picture gets wavy and fades to black or purple then black. I leve it off for 10 min then same story.

I thought it was a power issue so i swapped the 7805s. No difference. I reflowed the huc videochip. Seemed to get picture a bit longer but no dice.

When the picture disappears, the sound goes out to. Would a bad video huC also remove sound?
Seems to me only a processor halt would kill both sound and pictue?

Any ideas where to look? I tried with composite. Same thing. Broken via? Badly soldered cap? But where?

Appreceate any tip or idea.

Thanks
/Nichlas

[SignOfZeta]

A short.

[blueraven]

It sounds like you're losing power to the RGB chip.

Are you using an original power supply? if not what voltage/amperage is it? Also what kind of SCART or JP21 connector are you using to run to the RGB TV? Do you have another to test to rule out the cable?

Also have you checked for a bad ground anywhere or as Zeta mentioned, a short to the chip? Time to get out the multimeter.

Ideas for places to start, anyway.

[SignOfZeta]

I assumed from his way of speaking that a good power supply was being used (must provide a full amp) but normally that's the first thing I'd say. He's losing power one way or another. It's either the source or a short is consuming everything.

Hook a meter inline with the DC supply and watch the problem occur again. Do this with a HuCARD game. If the total current consumption is more than 500mA (probably if more than 300mA) then you have a short.

CD gaming consumes more power and the high current demand is usually only needed when the laser sled is moving. If just running a HuCARD then you shouldn't even need half an amp.

[NichlasEk]

Thanks for the replyes. I cut the red wire and messured amparage. Got a peak of 0.498 (inrush?) then it whent down to 0.482 and held stable for a minute or two. Picture and sound whent out after 10s. So if its a short. Its a small one.

Then i leave it again for 10-15 min. Same thing again.
Could it be a buildup of capacitance within an ic? Maybe a bad decoupeling cap or a bad connection?
I did ohm out the rgb chip and compared with a working one.
Almoste the same resistance.

This one is kind of a headscratcher to me.

[SignOfZeta]

Can your power supply actually make more amps than that? What is voltage across the DC in when the system dies?

[blueraven]

Thanks for the replyes. I cut the red wire and messured amparage. Got a peak of 0.498 (inrush?) then it whent down to 0.482 and held stable for a minute or two. Picture and sound whent out after 10s. So if its a short. Its a small one.

Then i leave it again for 10-15 min. Same thing again.
Could it be a buildup of capacitance within an ic? Maybe a bad decoupeling cap or a bad connection?
I did ohm out the rgb chip and compared with a working one.
Almoste the same resistance.

This one is kind of a headscratcher to me.

This could be a bad cap.

Can your power supply actually make more amps than that? What is voltage across the DC in when the system dies?

This is a really good point. It makes sense that the Hu-Cards are working with a low power draw, and I've had a similar issue with CD boot when using a cheap, generic powersupply. Not enough power to run the laser assembly.

My bet is that the supply is malfunctioning/incorect, or you have a short going to the laser/CD assembly. 

OP, what power supply are you using? Is it the original NEC one or an aftermarket?

[NichlasEk]

Sorry, wish it was the supply. Have tried 3 diffrent supplys. All working on the other duo. Even a 3 amp one.Will look for shorts or bad connections an hour a night.

Have a broken pcengine incoming, if nothing works il tr swapping the huC6860 with that.


Thanks.

[blueraven]

Sorry, wish it was the supply. Have tried 3 diffrent supplys. All working on the other duo. Even a 3 amp one.Will look for shorts or bad connections an hour a night.

Have a broken pcengine incoming, if nothing works il tr swapping the huC6860 with that.


Thanks.

You might want to wait before swapping the chip to compare multimeter reading with others on the forum, or hear what the other techs have to say. Just a suggestion. We're two of opinions of many.

[NichlasEk]

I think thats a good idea. Read a little more. Migt be a SRAM error. Il probe it out and then order some new. Found original sram on aliexpress, hate to wait a month for shipping tho. Does anybody know of a modern replacement for the SRAM?

[blueraven]

There are a few SRAM fixes in the mod forum where you can do an upgrade.

Look in Necromancer's post  Right Here, which collects all of the repair/mod threads.

The thread you are looking for is the BRam Upgrade Hack by wilykat and the FRam Duo Mod by Vimtoman. Hopefully this will keep you preoccupied until the others weigh in. 

[NichlasEk]

Thanks. That looks like a fun project. Will try in the future.
But I was thinking of the SOP28 packages sitting next to the huC6870. They seem to handel sprite data in tandem and they had a lot of old hard flux on them. Might they be callef scratch ram? Or am I way off?

Founf this on Aliexpress: LC3564QM-10

[SignOfZeta]

The correct diagnosis, whatever it is, can be found with a meter.

What is the voltage measured across the DC input as the system fades out and dies?

[NichlasEk]

O, it dosent fade out any more. After cleaning the board and touching up some legs and vias i get a good picture with stable sync, but with grapchical curruption like the image i uploded.

And the voltage after the 7805s is just about 5.1-5,2v. Have a stable 5v on the hucard slot and a lot of the caps to. Som caps have lower voltage then others, but i think its supposed to be that way.

I dont have a logic probe. But i have a small cheap scope that im not used to using. But i guess i have to at some point.
Git new lasers to day. Going to try them now. The one on the unit had a torn ribbon cable.

[MobiusStripTech]

Glad to hear you solved the issue. This was definitely a weird one.