Author Topic: help identifying previous mod/repair to japanese Duo R + troubleshooting  (Read 158 times)

tonydanza666

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Hello all,

thank you for accepting me into the forums and taking the time to read my post,

have always had an interest in these NEC machines however never owned one as I don't believe they were sold in retail stores over here (Australia), I have just received 2 rough looking Japanese Duo R machines from a junk lot untested, half expected there to be problems so I'm prepared to do a bit of leg work to maybe get them back up and running if its even possible.

Only opened/tested one machine first, still waiting on AV cable which hopefully arrives today but noticed a few things straight off the bat with this first machine, hoping someone can point me in the right direction or shed some light on what's been done in that past to it.

before powering it on i took the case off and inspected the board and it looked great, caps were fine and no damage it seemed so i powered it on expecting to see some kind of LED but no luck. thought maybe the LED only lights up with a disc so put a disc in, no laser movement or any attempt to read it (I had the cable for lid connected that tells the drive its been shut) - seeing as i don't have an AV cable yet my first question is does the machine have a power LED? ie does the 'busy' LED light up and then blink when the disc is being accessed.

Afterwards i checked a few points with the multimeter while powered on and got readings between 1-5v at various spots most notably the av port 5v on one of the pins which i guess was a good sign

lastly i powered it off and took the whole board out to look underneath and found 2 areas that have either been repaired or modded and hoping someone here can shed some light on what has actually been done so i can get a better understanding.

The first image is IC512 and looks like the original chip has been desoldered and replaced however the legs don't line up and only a couple of legs have actually been connected to the pads. After a bit of googling it looks like some type of 32k static ram, would this have been some type of upgrade or dodgy replacement attempt?  Also are there any type of service manuals or schematics for these machines floating around? I've found the cap list and some IC information but that's about it so far

Second image is the underside of the controller port, looks like a trace has been cut and then bridged to the point next to it, I'm assuming this is a repair?

Anyway, thanks for reading. looking forward to learning more about the machine and will find out when i get the AV cable if there's any type of signal. Still haven't opened the other one to take a look but judging by the outer case I'm not expect much from it either. Hopefully i can get one machine working out of the 2


tonydanza666

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Re: help identifying previous mod/repair to japanese Duo R + troubleshooting
« Reply #1 on: December 11, 2021, 12:27:59 AM »
so the AV cable arrived, getting a video signal but just a white screen (no card or cd inserted) switched it on the second time and now getting a pale blue screen

tried second console and that gets a beige screen (still haven't opened that console)

currently poking around with a logic probe, i'd assume these screens indicate something failing before it gets the all clear and boots the bios.

Keith Courage

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Re: help identifying previous mod/repair to japanese Duo R + troubleshooting
« Reply #2 on: December 14, 2021, 12:06:13 AM »
Looks like someone went to replace that chip and didn't finish the job for whatever reason.

Can you solder? I'd definitely solder that chip in there correctly before doing any more testing.

What you see at the controller port is normal. I've seen this type of thing done on a whole bunch of DUO-Rs(stock).

tonydanza666

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Re: help identifying previous mod/repair to japanese Duo R + troubleshooting
« Reply #3 on: December 15, 2021, 02:42:32 AM »
Looks like someone went to replace that chip and didn't finish the job for whatever reason.

Can you solder? I'd definitely solder that chip in there correctly before doing any more testing.

What you see at the controller port is normal. I've seen this type of thing done on a whole bunch of DUO-Rs(stock).

Thanks for the reply, I think you're right. I've left that machine for now and moved onto the second machine which i've had some success with.

First time i turned it on i got a 'beige' screen, not white but an off white color.  I ordered a couple of turbo everdrives which showed a few days ago and lo and behold the machine with the beige screen booted into the file explorer and i can run all of those games fine!

Next i loaded the CD-ROM bios off the everdrive and tested a genuine game disc and it loaded fine! So it seems everything is working on this machine but it doesn't load the CD bios if there is no card inserted.


tonydanza666

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Re: help identifying previous mod/repair to japanese Duo R + troubleshooting
« Reply #4 on: December 17, 2021, 06:38:54 PM »
So i've de-soldered that dodgy chip,

I've taken out the 2k x 8 chip SRAM Chip from a Ten No Koe 2 which is identical but a different size, I've wired it up like a modchip and checked my work with a multimeter. There's no markings for pin 1 so I assumed bottom left when looking at the writing on the chip the correct way up.

I have no way of telling if the chip from the Ten No Koe 2 is good or not but i do have a pile of others i can salvage from if need be, I powered it on and same pale blue screen.

Just for the record after i desoldered the bad chip and cleaned it up I tried powering it on without the chip at all and got the same blue screen. I'm fairly confident I've taken care of this SRAM chip but I'd love to get some clues on what the blue screen relates to if anyone knows. I'm sure its an error code of some sort that could narrow the troubleshooting down a bit.

The other console is working fantastic, plays CD-R's without any adjustment and everything works like a charm