PC Engine Duo - Super System BIOS problem

[CloudGamerX]

Subject:
PC Engine Duo

Problem:
Super System Card bios does not work despite regular hucards inserted working fine,  signs of previous region mod present and repaired by individual. Full cap kit was installed by previous owner.

Attempts:
-Reflowed RAM
-Reflowed previously severed card slot pins
-Reflowed Sony chip associated with CD Drive
-Voltage check, passed

[Keith Courage]

What happens if you try use system with your own CD system card? This can help determine what's at fault.

Also, was that a gamedoctorhk DUO? Looks like the super tiny capacitors he uses in your pic there.

[CloudGamerX]

I do not own a Super System Card sadly, and this was from gamedoctorHK.

[Keith Courage]

I've worked on a lot of these which is how I could tell who had worked on it prior. Basically anything gamedoctorhk sells that is listed as junk usually has some pretty odd issues. Otherwise he would have fixed them himself since he sells systems as well. In all honesty I would get a hold of thesteve here in the forums. This problem sounds like it could be a bad chip on the motherboard and that type of repair is right in his wheel house. 

Oh, one more thing I just thought of. It might be bad traces going from the pins of the Hu card slot. This can also cause the no bios on startup. Especially since you said a region mod was done before. Maybe whoever did the region mod damaged something. Check the traces underneath the board to see if they all have continuity for the pins that had been tampered with.

[CloudGamerX]

I checked the underside of the console and I got nothing. The traces aren't broken for the HuCard slot. Nor do i see any broken traces anywhere on the board. Testing continuity for the underside, connections are solid. So I am convinced it is either bad RAM or a bad BIOS.the BIOS part will be next to impossible to replace without sacking an original Super System Card

[Keith Courage]

typically the symptoms of bad Ram is that the system will still turn on and work but you will get glitchy looking graphics. so most likely not the ram.

[Eddiesamma]

There is a multiplexer chip above the hue card slot, seems to be functional mostly as it is loading the hue card roms but isn't switching to the on-board rom when the slot is not detected. If you can find the pinout of said multiplexer you should be able to determine if it's held low or high when the slot is present and go from there. Also could be that it's a short on the slot continually holding it high as if a card is present. Google hue card pinout and check for +5 on any pins that shouldn't have it.

[mickcris]

I have a duo-r that has this same problem.  i messed with it a bit before giving up.  i assumed it was a bad IC somewhere as I couldnt find any issues with traces

[Eddiesamma]

Did a little research (google) and seems pin 1 is card detect. Hope this helps. If you can shoot me the label on the chip to the top left of the slot I can find a datasheet for the multiplexer and maybe help a little more. But for now you can check the voltage in pin 1 with and without a card inserted to see if it's stuck reading that a card is active in the slot. Or hit theSteve up who probably has this stuff memorized and can point to point tell you exactly what's wrong lol.

[Eddiesamma]

Edit* top right of the card slot.

[thesteve]

I mapped and posted the mapping chip
Search it on here, full pinout in text file

Sent from my HTC One_M8 using Tapatalk

[CloudGamerX]

Okay, so i found the problem immediately. Pin 1 on the connector has 5v running on it  . The traces seem fine, so why is 5v running on Pin 1? That pin is Card Detect. I think when i checked the pin connector originally, i checked it with power off  :oops:

[thesteve]

thats not it
that pin has 5V without card and ground with

[thesteve]

almost every time its a missing address signal to the mapping chip under the board
most of the 22uf caps by the card slot are power filtering for buffer chips on the address bus, so a missing voltage there will do it
also checking signal at the mapper with a scope or logic probe should quickly find it
http://www.pcenginefx.com/forums/index.php?topic=16503.0
that has all the signal info to solve your issue