Duo giving corrupted graphics on power up

[D-Lite]

Ok, the title is not telling the whole tale. 

Working on a Duo for someone and the problem is that on power up, you get one of these events:
1.  solid color screen, sometimes with a hum
2.  graphic and sometimes sound distortion (jumbled, not blurred/wavy)
3.  perfect startup and play

Now this happens with both HuCard or the BIOS screen, so it doesn't appear to be slot related.

Things I've tried so far with no change in outcome:
1.  Replaced all large caps
2.  Swapped AC inlets
3.  Replaced the fuse and diode
4.  Different power supplies
5.  resoldered all cart slot points
6.  Resoldered at heat sinks/voltage regulators
7.  Checked all IC contacts for shorts

The only thing I can find that seems a bit unusual is that the voltage at the voltage regulators is coming in at 12.4V whereas on other systems I have it's more like 11.2-11.4V.  The regulators are putting out the normal 5.0V, but I'm wondering if the voltage coming in is the problem.  The problem there is that like I said all points leading into the regulators have been either swapped or checked and seem fine. 

WHAT AM I MISSING????

[SignOfZeta]

RAM?

[kattare]

Is there any pattern to the 1/2/3 events at boot?

eg, always 1 after it's been sitting an hour, always 3 after it's been on for 5 mins, etc, etc, or does it appear to be completely random?

I think my next step would be to replace the 7805's, but that's mostly a stab in the dark.

[rag-time4]

My Duo is consistently giving symptom 1: solid color screen, sometimes with a hum (but mine always has a hum)

[D-Lite]

Is there any pattern to the 1/2/3 events at boot?

eg, always 1 after it's been sitting an hour, always 3 after it's been on for 5 mins, etc, etc, or does it appear to be completely random?

I think my next step would be to replace the 7805's, but that's mostly a stab in the dark.

Totally random which makes me think it's a power problem.  The leg into the regulators is already high, don't know how or why.

[blueraven]

D-Lite,

Does it look anything like this? hucards gameplay worked fine on this one:

https://www.pcengine-fx.com/forums/index.php?topic=6033.msg101922#msg101922

[D-Lite]

D-Lite,

Does it look anything like this? hucards gameplay worked fine on this one:

https://www.pcengine-fx.com/forums/index.php?topic=6033.msg101922#msg101922

Sometimes yes.  But there are times where it just completely fails on power up with only the solid color screen. 
Did you get the RAM swapped?  SoZ, any experience with the RAM failing like this and affecting overall startup?

[rag-time4]

D-Lite,

Does it look anything like this? hucards gameplay worked fine on this one:

https://www.pcengine-fx.com/forums/index.php?topic=6033.msg101922#msg101922

Raven you never finished off that thread. What happened with round 2? Did you post a separate thread on it?

[kattare]

D-Lite, if you plug the same power supply (ac adapter) into another duo and test at the input side of the 7805 what do you get?

I'm still thinkin' I'd replace out the 7805's, but if the voltages at the inputs are different on a working system with this same adapter, maybe there's a cap leak induced short somewhere along the line causing random behavior?  Or maybe a broken solder joint on something that should be causing a voltage drop?  kinda like the DIN solder points that crack and are impossible to see, but video doesn't work until ya fix 'em...


Blueraven, I'm really curious too, whatever came of your RAM swapping project?

[SignOfZeta]

SoZ, any experience with the RAM failing like this and affecting overall startup?

Nope, none at all. I was just throwing out the only thing I could think of.

[unclebugspayton]

Shit D What kind of person would send you a duo like this?