Question about the DUO/R/RX's save data cap

[SegaSonic91]

I'm wondering if it can be increased with a bigger cap?  I have a PCE DUO that I am in the process of re-capping and fixing up in general and I see the (power??) cap on the board but have no idea where it is on the RX or IFU.  I hate the back up RAM in the PCE systems.  I have lost many, many saves over the years due to not turning the system on for a few weeks.  If the time the memory is saved for can be increased AND the amount of save data memory can be increased, that would be awesome!  I never understood why the hell NEC did not just put a battery in the system like the MEGA-CD has.  I still have saves in my MCD from 1993!

[schweaty]

Edit - bad info on my part

[SegaSonic91]

Thanks for the reply.  I will give it a shot in the DUO and see if it helps at all. 

Also, about your SEGA-CD, it's strange that you have to turn it on to keep it charged.  I can go months without turning my JP MCD on and it never loses the internal saves.  My original release day PAL MCD still has all of the saves from 1993 onwards and it was not used for years.  Same with my PAL MCD2 and Victor Wondermega. 

I have the "have to turn on often to not lose saves" problem with my RX.  I don't know how many times I've started Tengai Makyou II, Cosmic Fantasy 4 Chp1, Dracula X, Startling Odysey 2 and many others because of lost data from not turning the system on for a few weeks.  My original PCE I bought in 1996 with 70 odd games was a "suitcase" IFU system.  When I got my RX in 2004, I thought that the internal memory would be far superior to the rubbish IFU internal memory.  I was wrong. 

I guess NEC was too cheap to increase the size and made people rely on the Ten no Koe cards.  When I had saves of the above mentioned games, among others, I deleted them because I did not speak/read Japanese back then.  Very annoying to say the least!

[MNKyDeth]

I thought the SuperCap's were based more on the voltage?

The cap that comes in the consoles by default is a 0.047 uF 5.5volt cap.

It's like a battery so the voltage would need to stay the same at 5.5volts but you can increase the capacitance to say a 1.5 Farad cap and the data should be retained for a much, much longer period of time. I have not tested it but this is assumed,implied I thought.

The normal caps the uF rating needs to be the same but I thought this one particular cap was like a battery so you needed to keep the same volts but increase the Farad rating for better longevity.

Please correct me if I am wrong as I have been putting in these larger caps into my machines.

I use this cap in all my Duo-r type machines. White
http://www.mouser.com/Search/ProductDetail.aspx?R=EEC-S5R5V155virtualkey66720000virtualkey667-EEC-S5R5V155

I use this cap in all my TurboDuo/PC Engine Duo's. Black
http://www.mouser.com/Search/ProductDetail.aspx?R=EEC-S0HD334Vvirtualkey66720000virtualkey667-EEC-S0HD334V

There is a lot more space in the Duo-R's so I was able to fit a much larger cap in it.

[SegaSonic91]

Awesome!    Thanks for the links!   

I will replace both the RX and DUO super caps.  The cap is very easy to notice in the DUO, but I have not seen anything that sticks out at me, super cap wise, on the RX board.  I assume it would be the same as the R.  Where abouts on the board does one find the battery cap?  Thank you so much for your help! 

[MNKyDeth]

The SuperCap on the Duo-R boards is located at C509. In between the A/V DIN and the 7805 Heatsink closest to the Din.

I have a Duo-RX here that needs repair and the PCB motherboard looks exactly the same as a Duo-R.

You can see the large cap just above the RGB amp on this install I did. I put a piece of electrical tape on the PCB then poked the SuperCap legs down into it and soldered the bottom. I did this because there is trace test dot. <-- Lack of better words... Right next to the legs and since the large cap has a larger leg I wanted to make sure it doesn't touch anything it's not supposed to.



This is in a PC Engine DUO. It's the black cap in the bottom middle of the image with arrows on it pointing to the left.

[CatPix]

So the memory is backed up with a super capa? How long can it last?

I know of a PC-Engine Duo that was left stored for at least 3 months (from August to mid-November) and when I powered it on, I saw saves insides. It seems a very long time for a capacitor to hold saves....

[deubeul]

I replaced the backup cap on my IFU last week for a 1F supercap. Until that, the saved data were gone after 5 minutes off, all I can say is now it holds at least 3 days! 

[wilykat]

It is possible to increase beyond the stock 2k save RAM and use DIP switch or something to select banks.  On Tennokoe2 it is a large DIP chip and it is easy to replace it.  I don't have Turbobooster Plus to check with as picture seems rare.

I'll have to look inside my Duo-R to see where it is and what kind of chip it used.  If it is a DIP style, it could be easy job but if it's SMD or a dual 4-bit RAM chip or something funky, forget it.

I still have a few 32k SRAM (256x8) around that I could hack in with 4 position DIP switch (or a rotary binary switch) to select one of 16 banks.  I will probably need to beef up the super cap to handle larger SRAM.

The hack should be as easy as:
D0-D7 pin for pin
2 enable lines
R/W line
A0-A10 pin for pin
ground and VCC

Then wire A11 to A14 to the switch. 10k Pull down resistor on each of the 4 address to ground for when the switch is in off position, and the switch common to 5v to pull up address line when on.  10k resistor prevents shorting 5v to ground, and pull down to ground is required to avoid floating address that can cause unpredictable result.

[Vimtoman]

I think they are OKI serial memory chips.

[SegaSonic91]

I bought a bigger cap for my DUO I am recapping at the moment.  Will have to see if it works once I have the thing up and running.  I plan to do the same with my RXs', IFU and SG+SCD2 

[wilykat]

Since there isn't much detail I can find about Duo-R and RX saves, I opened my R and poked around a bit. I think I figured which cap is for the save RAM: a tiny 0.022uF but it is the only one labeled for 5.5v and next to the 2kx8 SRAM chip.  The chip is on the bottom of the board at IC512. The pin 24 is VCC and goes to a diode (that looks like transistor) which separates the cap power from the main 5v so SRAM can retain power without having the cap drain dry to the whole system


SRAM on top right side. The 2 large solder spot between R543 and the SRAM are the cap leads.

The cap on the top side:


Replacing that cap with something bigger and is at least 5.5v will help retain data longer.  I don't know if I will replace the SRAM chip with something bigger as it is smaller than I thought.  Tennokoe2 used the larger DIP package that is easier to work with. SMD IC is not as easy to work with.

[Vimtoman]

It is possible to increase beyond the stock 2k save RAM and use DIP switch or something to select banks.  On Tennokoe2 it is a large DIP chip and it is easy to replace it.  I don't have Turbobooster Plus to check with as picture seems rare.

I'll have to look inside my Duo-R to see where it is and what kind of chip it used.  If it is a DIP style, it could be easy job but if it's SMD or a dual 4-bit RAM chip or something funky, forget it.

I still have a few 32k SRAM (256x8) around that I could hack in with 4 position DIP switch (or a rotary binary switch) to select one of 16 banks.  I will probably need to beef up the super cap to handle larger SRAM.

The hack should be as easy as:
D0-D7 pin for pin
2 enable lines
R/W line
A0-A10 pin for pin
ground and VCC

Then wire A11 to A14 to the switch. 10k Pull down resistor on each of the 4 address to ground for when the switch is in off position, and the switch common to 5v to pull up address line when on.  10k resistor prevents shorting 5v to ground, and pull down to ground is required to avoid floating address that can cause unpredictable result.

Binary switch sounds good.
What about using Fram?
No cap then.

[SegaSonic91]

I checked my open IFU that I am going to RGB mod and found the save cap.  It looks to be exactly the same as the green 0.047uf NEC cap that I replaced in my DUO.  Has anyone swapped that cap out?  It is sandwiched between the main board and a smaller board which will make it both hard to remove and also, to replace with the newer, larger radius cap I put into the DUO.

EDIT: In relation to the picture you posted of the DUO, MNKyDeth, I am thinking that I may buy another supercap in the style of the one you have in your boards.  The 1000uf cap I put in is about half the height of the original green NEC cap, but about twice as wide.  I had to solder a leg of a cap under it.  I worry that it may cause a short.  I figure that your style may be better for the DUO and I may try and use the currently installed cap in the IFU, instead.

[thesteve]

the smaller board is socketed so that wont be as hard as it looks