Graphics Glitch - DUO

[thesteve]

often if touching the pin changes the pic its a bad trace, but an open chip could do the same
what pins made it change?
if it was an address line, its not getting connection to the vid chip

[mamejay]

Finally got around to getting some memory chips.  Sourced them from Germany

Started with the first one.  one leg was stuck and ripped the pad up so had to trace back to a point to solder a wire to it.


Decided to try it before changing the other one.  Success!!!


Thanks to all for the advice guys.  Another DUO saved from the scrap heap.

[thesteve]

awsome

[Keith Courage]

May I ask where you bough the chips from?I cannot seem to find them from anywhere that doesn't require an order of like 50 or more.

[mamejay]

May I ask where you bough the chips from?I cannot seem to find them from anywhere that doesn't require an order of like 50 or more.

http://www.ebay.com.au/itm/170895817675?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
This is the guy i brought them off

[HercTNT]

love a happy ending, nice work!!

[Sensato Black Lion]

I've got a Duo with a similar problem here.

Some screens look perfectly fine, some are incredibly glitched. The glitch display pattern is different from one screen to another but pretty much the same pattern for a said screen each time I encounter it.

I do not know if the problem is only related the the Hucards since the system is unable to read discs at this time.

I have changed every caps, I've swapped IC 904, 905 and 906 with known working ones... no results, I get the same glitches.

Any idea what I should check next? I'm thinking about reflowing the 6270's pins since it seems to communicate directly with IC 904, 905 and 906.


Sample pictures:

[mamejay]

Yeap that looks definetly like the memory modules issue to me.  I would be replacing those.

[Sensato Black Lion]

That's what I thought too. The only thing is, I've already replaced them and it didn't solve a thing.

These screenshots were taken after I replaced the memory chips. There are exactly the same as they were with the original memory chips.

[Sensato Black Lion]

Well well, after countless hours or probing with an oscilloscope and replacing ICs, I was about to give up and put this system aside for good. That is when, out of nowhere, my eye spotted some corrosion UNDER the Hucard slot. I don't know why I lifted the slot to look under it but, there it was, a LITTLE corrosion spot on a via. This is what it looked like after I cleaned it (can't really see well...):




It appeared rather innocent but just in case, I cleaned it and did a continuity test to see if everything was ok. Turns out that little corrosion had cut the trace. I couldn't believe it! Could that be it? I redid the trace like this:



Tried the system one last time, and it worked! At last! I must have spent a dozen hours trying to fix this.

It was definitely related to the VRAM chips but for some reason, when comparing the signals on the chips with a working Duo, I couldn't see any major difference.

That via was nowhere near a leaky cap, I'm really wondering just how it got eaten by corrosion like that.

Thanks to everyone who helped!

[mamejay]

Another one brought back from the scrap heap.  Well done on the find!!

[Fidde_se]

This is because of moisture in the air, when the pcb manufacturer makes the circuit board out of laminate (glassfiber) and copper they are blowing liquid solder over the whole board so that the copper don't corrode, sometimes this doesn't get everywhere and the copper is exposed, especially in the vias, usually a green varnish is covering the parts that are suppose to not get soldered, time and the elements will corrode exposed copper in time

[Fidde_se]

I just thought I should give you all a crash coarse in VIA fixin.

From the picture you seemed to fix it by just finding where it leads and then taking a simple wire, while it works terrific, when doing other stuff while it's open you might get stuck in the cable and rip something apart and the pro way is also so much nicer, anyway this is how, no astronaut stuff but here it goes.


Heres a VIA thats not working


Here it is again, a little closer =)


Take a scalpel and scrape some of the pads surrounding it, do it on both sides.


Take a single wire, theres lots of different diameters for vias, take one that fits.


Bend the wire over the scraped part, on both sides.


Solder it, both sides, DONE! check for continuity, it should now work.
Note that it may only work on PCBs 2000 and older as newer ones can have
like 16 layers and be connected at several places inside the via, but for PCE
stuff no worries. Take a cottonstick and some alcohol and take away some
of that flux.


Here is just another PIC with a ballpen to get the feeling of how small
they can be, even if this was a fairly large via.