Dead pc engine duo

[Mrwoodchuck]

So I pulled ic520 from both units. They are still acting the same as before, checked around the cluster of Hudson chips still can't find anything.

Man these are a pain in the butt.. Lol

[thesteve]

Yes they are
Without a cart, and 520 removed, probe all the address and data pins at the slot (pinouts on line)
The data pins (D0-D7) should be high
The address pins all pulse

[thesteve]

If good,  insert cart
Recheck data pins (now pulsed)

[thesteve]

If all good replace ram chip

[Mrwoodchuck]

this is gonna be a long one.

system 1

without card

1 h
2 dead
3, 4 l
5 - 10 h
11 - 14 dead
15 - 17 h
18 gnd l
19 - 23 h
24 dead
25 h
26 dead
27 h
28, 29 l
30, 31 h
32, 33 l
34 dead
35 - 37 h
38 5v h


with card

1 l
2 dead
3 l
4 - 6 h
7 - 10 l
11 - 14 dead
15 - 17 h
18 l gnd
19 - 23 h
24 dead
25 h
26 dead
27 h
28 , 29 l
30 , 31 h
32 , 33 l
34 dead
35 - 37 h
38 5v h

system 2

without card

1 h
2 d
3 pulse
4 l
5 - 12 pulse
13 dead
14 pulse
15 - 17 h
18 gnd l
19 - 23 h
24 - 29 pulse
30 l
31 pulse
32 l
33 pulse
34 h
35 l
36 h
37 h
38 5v h


With card


1 l
2 dead
3 pulse
4 l
5 pulse
6 pulse
7 - 12 pulse
13 dead
14 - 17 pulse
18 l gnd
19 - 23 pulse
24,25 pulse
26 pulse
27 pulse
28 pulse
29 pulse
30 l
31 pulse
32,33 l
34 pulse
35,37 h
38 5v h

System 2 IS ALIVE!!!  apparently pin 13 was dead the connection from ic906 and pin 13 was damaged even though i looked and the trace was fine still no continuity.. I popped in my only jap game and it worked, so at this point put chip 520 back in and try again i assume? and if the 520 is back in and it does not work i assume replace that chip.

System 1 is just all over the place, it seems like the 6280 is dead?

[thesteve]

sys1 isnt  clocking
check clock pulse (likely good)
replace 6280

[Mrwoodchuck]

Awesome, thank you for all your help thesteve!!

I don't have my oscilloscope its in storage I will have to grab it later.

Is there any location you know of to buy the 6280 or is that a situation where i will have to pull one from a dead system?

I feel like I should bake you cookies or something for all your help. and i'm being serous.

[thesteve]

gotta pull one

[Xenogears]

I have the same issue on a duo my friend asked me to check. Bios won´t boot, HUCards work finde, if I use a System Card and press Start, the screen shows "Please wait..." without the Detector switch for the Lid closed. I would like to start checking Traces from the Bios-Chip but do not know, where it´s stored. Could you help me out ? THX a lot !

[thesteve]

xeno your system has a fault in the interface
it could be a dead IC501, but more likely is a bad trace to IC501 or 1 of the small logic chips near the cart slot not running

[Xenogears]

I thought so but it just a simple VIA next a CAP. C519 Ground VIA leading to IC 517 was dead, so the bios did not start to boot. Connection reestablished and it worked. Once again a via issue... but thanks a lot Mr. TheSteve. Without your posts a lot of Duos would have been faded away 

[thesteve]

 thats what i was saying about the logic chips not running

[trapexit]

thesteve, thanks for this info. Are there any service guides for the Duo, Duo-R, Duo-RX floating around? Original or like the info in this thread? A step by step of what to check?

I just picked up a Duo-R that at the moment I don't have the history of unfortunately but it appears to be a botched video mod. The 6280 and 6260 were wired up and partially covered in silicon rubber. The wires were snipped so it's possible the mod was fine but the Duo-R stopped working so they just snipped the wires to get the components back.

Either way... the device turns on. Fuse and 7805's look fine. When on it displays a white or occasionally off white or blue or pinkish screen. Placing a HuCard in does nothing. I can post images of the 6260 or 6280 if interested but as far as I can tell there aren't any shorts or unconnected pins. I removed all the silicon rubber (that was a test in patience) and desoldered the wires left over and made sure to reflow the pins.

I don't have an oscilloscope or probes but with my multimeter it looks like the data pins are high as are the address pins.

Suggestions?

If I'm reading the thread correctly it was recommended to disconnect IC520?

[thesteve]

removing IC520 splits the system into PCE and CD system
that lets you rule out the cd system in troubleshooting
its not where i start, but if everything looks good it helps
also i have seen IC520 dead causing the issue

[trapexit]

And the IC520 on the Duo-R the same as Duo? Must it be removed or can a pin or two be lifted to accomplish the same?

I noticed C947 is not populated. Anyone know if that's expected?