Dead pc engine duo

[Mrwoodchuck]

Hi all,

I recived 3 duos from japan all with issues, i have so far fixed 2 of them..  O:)

But this last one has me stumped, I did some cleaning, replaced all the caps and all i get is a white screen mocking me when i power it up.

I replaced both 7805's and it reads 5v when the unit is powered on, i checked the cpu and all 5v pins are reading 5v.

There is no cards in the slot it should show me the load cdrom but it does not.

So i'm at a loss here, any input would be welcome..

Thanks

[pulstar]

Have you tried a HuCard/CD to see if you are getting any activity from the unit itself. Could be an AV port or output problem.

[Mrwoodchuck]

Sorry I failed to mention that,

I tried both jp, and usa cards nothing..
I hit the run button to make the drive start up like normal when you turn it on with no card in it, nothing....

thank you for the reply!

any other ideas?

[SephirothTNH]

Try doing an svideo type mod on it.  You only need to do the luma and see if you get an image.  That will bypass all the av stuff in the console since you solder straight to the Luma pin on the gpu. 

If you still don't get a picture than I would try replacing the ram chips.   Then eventually the big chips HuC62XX.

[Mrwoodchuck]

I think your on the right track with the ic's..

I tried to region mod one of my working ones and now it has the same issue as this one, white screen..

if i turn the power on and off quickly it changes colors, blue green white.. so on and so on..

I think i might have fried something when i was attempting the region mod, the fuse blew and everything..

So ya now i have 2 dead systems.. 

[BlueBMW]

Id wait for thesteve to chime in before you junk any systems.  There are other components on the hucard data lines that have beenknown to go bad and cause the same symtoms youre describing.

[thesteve]

Its changing colors/white screen, the 6260 looks good
Its likely just a broken connection
Logic probe if ya got it... start with the card slot
All logic pins must read a valid logic state

[Mrwoodchuck]

Thank you for the reply!

I Dont have a logic probe..
Right now all I have is a volt meter, I know not helpful in that situation.

I guess I will go and check for continuity on all the ic's starting with the 6260.

[Mrwoodchuck]

so I spent the better part of sunday tracing and coming up with nothing, I get payed on friday so i think i will spend a little bit of cash and get eather a usb logic analyzer or a logic probe.

what do you recommend?

I'm assuming the analyzer because i can save the data and easily compare it to another working console.

but it would be a cheap $50 and below one..

[thesteve]

a simple probe is all you need unless your reverse engineering a data bus

[Mrwoodchuck]

Ok, I will hopefully get one this weekend.

Is there any guide to see what signals i should be seeing?
I was thinking of comparing my working system, but it is acting a little funny too..

thanks for all your help thesteve, I appreciated it alot.

[Mrwoodchuck]

Well I am back, I got bought tools i figured i saw some of the saleae knockoffs and i would try one because they were so cheap.

I get my probe tomorrow but i tried the knockoff to see if there was data on the lines.
So my first power up and i found there was no data on pin 20 of the hucard connector.

i compared to my good one and on boot there is data on that pin.

Now the fun part, I reconnected it and wanted to make sure i was right on pin 20, well no pin 20 now had data but another pin "pin 22" had no data... and every time i power cycled it would bounce around..

so i am not sure if the logic analyzer is junk or what.

I will get my probe tomorrow and will report back what is going on then.

[thesteve]

lol, no they do that
your concern first is the data bus D0-D7 (the pins you clip for a region mod)
if any of them are stuck you have a shorted chip
if stuck there is a small bus chip connected by the slot (i have seen several die) pull it and test with card as bios will not be connected

[Mrwoodchuck]

Ok so i got my probe today, I have a pin stuck low every power cycle so it is down to that bus chip.

What is the ic number so i don't accidentally pull the wrong chip? Lol

In addition my second dead one has all high on the 15 - 23 pins not 18 as that is gnd..

[thesteve]

all high says the 6280 isnt addressing
your looking for IC520
note all 3 hudson chips and the ram chip by the card slot share that data bus and 1 or all of them could have a short do the same
pull IC520 first as its small and splits the system into a TG16/PCE and SCDR2 som you can work on the core system first