Duo-R saving issues

[wagamamalullaby]

Hello all,

I bought a Duo-R from a retro games shop here in the UK a few weeks ago, and I'm having issues with the file cabinet. I can press select on the bios screen and format the memory ok, but games don't recognise the file cabinet. Rondo of blood says backup memory not available after I press the run button, (then skips the prologue for some reason) and Ys says save format error when I try to save.

I bought a new supercapacitor from Console5 and fitted it, it hasn't made a difference. I noticed that the maximum voltage I can get on the supercapacitor is 4.78V, it won't go any higher, no matter how long I leave the console on. Does this sound right? The regulator outputs 5.10V and I don't know if this reduced voltage is my issue, though the spec sheet for the SRAM says it works between 4.5 and 5.5V, if I'm reading it correctly.

I managed to find an identical SRAM and replacing it hasn't made a difference, and I'm halfway through a full recap just in case a dodgy capacitor is bringing down the voltage leading to the SRAM. So far nothing has made a difference. I'll replace the rest of the caps next week but I'm not confident it'll fix the issue.

Does anyone have any advice or experience of this? I'm running out of things to check. Apart from the save issue, the Duo works great, plays CDs fine, and I RGB modded it while I had it open and I'm otherwise very happy with it. But the save issue is stopping me from playing Ys 1&2, and playing Rondo properly

If anyone can offer any advice, I'd really appreciate it! It's not a common issue at all from my hours of searching.

Thank you in advance.

[Keith Courage]

Check for bad traces going to or from the LC3517 memory chip. Right in between the Heat sinks and the Large memory capacitor.  That would be my guess anyways. If no bad trace is found there, there look for bad connections/traces to the Large D91317GD chip.

[wagamamalullaby]

Thank you for your reply and advice. I'm buzzing out all the traces using my multimeter and drawing up a diagram. I've spend about 5-6 hours in total hunched over this board now over the last week!

I lifted the Vcc pin 24 of the SRAM and soldered on a cable directly from the output of the 5V regulator and the problem remains so I'm convinced it isn't a voltage issue anymore. I checked the areas you mentioned and everything looks fine so far. A few near breakthroughs, until I discover a via hiding underneath the glue holding the IC. A couple of areas I've still to investigate, I'm suspicious of a transistor directly below the super capacitor at the moment. I followed one of the traces from the SRAM to there, and it seems that the base pad isn't connected to the copper trace running away from it. The trace is tiny though and barely visible, leading to a resistor. I'll need to do some more investigation before soldering a cable to bypass just in case I cook the transistor. I'll also need to take pictures too as it's such an uncommon issue and should be documented in case anyone else has this in the future. Assuming I find the problem though.

Again, thanks for your help. I'll update if I discover anything new.

[Keith Courage]

I've only come across a save issue problem on two systems. One had a bad trace. 2nd had a bad memory chip but you already changed that.

[wagamamalullaby]

I fixed it. It was the tiny transistor that I was suspicious of. On the spec sheet for the sram, the pin this trace is part of is ‘write enable’, which was my issue to begin with, so I was very hopeful that this was the problem. Here’s how it looked (zoomed way in):

https://ibb.co/Tbzpqt2

That tiny break between the base and the trace near it was the issue. I soldered a tiny cable between the base and resistor. I’ve no idea if it was a problem that developed over time, or if it came like that from the factory originally. But I’m over the moon that I found the issue.

Anyone discovering this in the future, as Keith Courage says, check those traces closely!

Thank you for your advice. Now for some playing!

[Keith Courage]

Glad you found the problem. Weird how that spot/trace was messed up.