Turbo Duo with memory save issue (finally solved)

[turbokon]

I have a turbo duo that doesn't hold memory save in its ram. If I turn off the system and power on right away it holds the save. But after a few seconds it doesn't hold. The voltage at pin 24 of the IC drops continually after power off. I have replaced the super capacitors, the diode and the IC ram and still getting the same issue. I've been working with thesteve and I'm running out of ideas on what to check. I have tried two different type of super caps with no differences. Have any body ran into this type of issue before?

[Marll]

Is it just caps that power the IC for RAM saves? I've never looked in the Duo and always assumed there was a CMOS type battery that did this. Though the cap thing makes more sense, as you can leave a Turbo powered off long enough and everything is lost.

[turbokon]

The super cap is what the duo uses as battery for the IC ram backup. The super caps acts as a battery because voltage is stored and dissipate slowly unlike regular cap.

[turbokon]

It's like something is sucking the voltage after its turn off. I tested the super cap with a battery an it's hold the charges like it should. The orange component is the new super cap I installed.

[NightWolve]

You know, I was just thinking about asking Steve what the best value is to replace that Backup RAM cap with, and, if it's OK to just put a higher value than before. More farads should be safe and just equal a cap that takes longer to discharge, no? But yeah, the highest value my cap kit came with is 1000 uF, so I wanted to find out if that'd be OK to use.

Yours is a Japanese model I take it ? The cap in question is a square black one, like the one I circled with 5.5 V and 473 written on it, right ??



As far as I know, that is the cap for the Backup RAM, etc. I actually made a thread about this in the mod section because I wanted to know which cap it was and to possibly change it to a 3 Volt lithium battery. I guess the square black box in your PCB is a choke thingy enclosed in plastic.

Anyhow, must pester Steve again! Also, what is the value of this orange super cap you installed? Got it from Digikey or ?

[ProfessorProfessorson]

Yeah its the black block. If you want the part info for a suitable NEC replacement its the following:
part number FMC0H473ZF  NEC Tokin America, Memory Back-Up Supercapacitors, THT 5.5V 0.047F

If I remember right anyway...

[NightWolve]

It's in Farads? Oh wow, I was REALLY off then in hoping my 1000uF one would work. It really is a "supercapacitor" then. I can see the .047 on turbokon's orange cap there, so you're probably right, but if it's .047 Farads that makes it 47,000uF, so that's quite a hefty cap then!!! Clearly a single order type item off Digikey or something.

[ProfessorProfessorson]

I'm not sure if Digikey carries the NEC issued one, but you can get the "can" type Turbokon purchased both off ebay, Digikey, and elsewhere for cheap.

[turbokon]

The one I used looks exactly like one used on my pc-duo with the same rating except the one on the pce duo is green.

http://bit.ly/TG3f9f

[turbokon]

I think I solved the memory problem too. Last night, I compare this to another duo and found pin 24 of IC ram traces to R544. The duo with the memory problem didn't have res at R544. Found the same res value from a cordless phone and solder it on R544. Voltage isn't dropping rapidly when turn off and memory seems to save. Powered the unit on this morning the save for gate of thunder is still there!! Woot! Woot!

[NightWolve]

So a resistor went bad ? How many ohms was it ? I thought resistors were the most least likely of components to ever fail.

[turbokon]

The resistor wasn't there to begin with, odd. However the pce duo I compared it to had it an the smd res value is 470ohm.

[NightWolve]

Thought I'd update this, add a new ProTip.

So, it seems judging from console5 that you can replace the super capacitor with a .1F model to double the memory storage time versus the original NEC .047F model!

http://console5.com/store/1f-5-5v-memory-backup-capacitor-for-nec-systems.html

YIKES, THESE ARE RUSTED TO SHIT USED ONES!

Instead of wasting $2.29 to buy one from them though, head over to eBay and buy a 5 pack for the same amount of money! If I'm reading it right, as a 1F, not .1F, that should make it last 10x as long! It's a NEC brand to boot!

http://www.ebay.com/itm/High-Light-5-Pcs-1F-Farad-Capacitor-Supercapacitor-NEC-TOKIN-5-5V-HGCA-/191443047755?pt=LH_DefaultDomain_2&hash=item2c92e5154b

This will only cost you $2.33 WITH shipping!!! I just ordered one for my Turbo Duo.

Make sure item is NEW, like this:

http://www.ebay.com/itm/1Pc-1-5F-Farad-Electric-Double-Layer-Capacitor-Super-Ultra-Capacitor-5-5V-C-/371160797535?pt=LH_DefaultDomain_0&hash=item566ae8515f

$2.47+$1.20 S/H = Not bad!

Compare that to the old link turbokon found with that guy wanting $6.50 for a 5 pack of the .047F model plus $2.25 for the shipping... Bad rip-off and no doubling or more of memory storage time.

Gonna check with Steve on the safety of this, though. A 5.5 Volt capacitor with 10x the capacitance value over the original should simply discharge for a much longer time and not present a problem/risk. NEC not using a higher value than what they did was hopefully just a cost issue and the .047F model simply provided a reasonable amount of memory storage time for the money.


EDIT: The Steve has spoken. The super cap can be as big as you want! Getting a higher capacitance model should merely just equal a longer discharge time and presents no safety issue! It's just a cost issue, but eBay for the win as far as the great deal I linked above!!!

[Brraap]

Thanks for sharing that, just ordered this

[NightWolve]

Cool, hope it works out for ya! Trick is desoldering that old one off.