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Zenith Z-Note 425 Lnc Video Issues.

FParker

Member
Joined
Feb 6, 2023
Messages
29
Okay, I have taken some time off from the Packard Bell to focus on an old project: the titular laptop. It's an IBM Thinkpad 300 with a different coat of paint.

It wouldn't boot when I initially received it in 2021, and because I'm a novice when it comes to computer diagnostics, I bought an old one that booted to BIOS off of EBay to aid me in that venture.

20230221_214743.jpg

As you can see, the motherboard has two levels: top level has processor and RAM, bottom level has power and drives. I should note that the left board (top) is from the "new" computer and the right board (bottom) is from my computer in this picture. The top board of my computer had some bad CMOS battery corrosion on the traces. I fixed those, and although it's not tidy, it works perfectly, as it is connected to the "new" bottom power board, and has booted to Windows 95 (my computer has a 160 mb HDD). Therefore, I have determined that the bottom board from my computer is the issue, and looking at it now, I think I've found some bad capacitors on it.

Before I bought the new computer, I read the description, and it noted video issues.

20230221_213929.jpg

I'm assuming the video is on the bottom board, since the issues stated in his EBay posting have carried over, despite the top board being from my computer. Granted, I cannot be 100% sure of that fact, but I just find it unlikely that it could be anything else.

The question is: how does one go about fixing this? I reckon the easiest way to fix this issue (assuming that the bottom board controls video) is to pull the passive components I need off the new computer's board and put them on mine.

I'm sorry if this is unclear. I will be happy to provide further elaboration, should it be needed. I've said "board" a lot😂.
 
Try taking the display out and throwing layers of tape where the lcd screen meets the frame on left and right sides. Sometimes a little pressure can fix horizontal lines. Done it on a few lcd's , usually with good results.
 
I tried it, but it, regrettably, did not work. I think it is related to whatever is causing this:

20230227_233632.jpg20230227_233634.jpg

What could cause something like this?
 
I would say that your video ghosting problem is the capacitors.

As for your problem with the line in the screen... I would take the bezel off of the top half and have a look at the screen itself. Maybe you have a problem with the soldering points between the brown or gray flat flex cable and one of the video driver boards.

Some people have had problems with the screens in Nintendo Game Boys and Sega Game Gears, caused by the separation of the cable from the conductive glue attaching it to the glass. It's usually fixed by being careful and pressing a hot soldering iron against the plastic tape-like cable. (It's heat-resistant. How do you think they attached it to the glass in the first place? ;) )

I would suggest that you post pictures here of what the flex cable looks like first, though, so we can make a determination.
 
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I have begun to open the bezel of the screen again, and now it smells like a dead, rotting fish in there. I'm assuming that would be the bad capacitor getting worse. I have been told in the past that a leaking or exploded capacitor smells absolutely terrible, but I've never experienced one first hand.

I will get it open and order new caps, inspect the flex cable, and post pictures here once it's done.
 
AHA! I knew it was bad capacitors! I've seen a similar ghosting, again, on a Sega Game Gear. I installed the wrong value of capacitor when I first repaired my now-departed original Game Gear (I have another one now, repaired as well), and it caused a weird white line to pop up on the display, and didn't go away until the system had warmed up a bit.
 
I have begun to open the bezel of the screen again, and now it smells like a dead, rotting fish in there. I'm assuming that would be the bad capacitor getting worse. I have been told in the past that a leaking or exploded capacitor smells absolutely terrible, but I've never experienced one first hand.

I will get it open and order new caps, inspect the flex cable, and post pictures here once it's done.

The dead fish smell means that the capacitors are actively leaking and need to be removed ASAP. Do not power the laptop on further until you replace the capacitors, because the leaked electrolyte is conductive and will cause electrolysis corrosion. The electrolyte is also corrosive and will eat the conformal coating/masking off of traces and can seep inside the PCB and cause irreparable damage.
 
Okie dokie, I finally got around to replacing the capacitors, and this is the final result:

20230314_005539.jpg

Sadly, the video errors did not resolve themselves (aside from the grey line across the screen). Looks like the guy I bought the computer from was right: there is something wrong with the display section of the computer.

To refresh, I am using the logic board from my computer and the power board from the "new" computer (mine did not even power on). This motherboard is a sandwich design. The LCD and VGA plugs are on the power board. What would cause these errors and how could I fix this?

20230314_010432.jpg

Also, despite the outcome after today, I still am pleased with the piece of work I managed in soldering all those capacitors. SMD is not my forte by any means, so the desoldering of the old and the resoldering of the new capacitors is most satisfying.

20230313_215148.jpg
 
If the graphical corruption is moving around the screen, I'd suspect either bad RAM, bad video RAM or a broken trace to the video chip, wherever it is.
 
I found the GPU:

20230314_025619.jpg


This link discusses it (although I wish it had more info).

I would assume the chips next to it are VRAM?

I don't even know how I'd go about testing for continuity or anything like that on this board.

I guess it's time to learn.
 
The chips next to the VDP are generic DRAM, either EDO or FPM. With their proximity to the VDP, they're probably for the chip.

Since that laptop is a sandwiched design, you couldn't do the normal tests, like pushing down on different parts of the chip while running to see if any broken connections come into contact again.

For continuity checks, you can get a magnifying glass and a fine pair of tweezers and poke the individual legs on the VDP carefully to see if any of them are loose. If there's a pinout, you could check from the legs of the chip to the various DRAM chips.

As for checking if the DRAM itself is bad, you'd unfortunately have to pull them at random and replace them with known good chips, since there's no easy way to test them.
 
I thought as much, but I just wanted to make sure I wasn't leaving any possible skills to learn on the table, if you know what I mean.

Hopefully I can find these chips.
 
Yeah, to the left, those are VRAM chips.

I wouldn't worry too much about the brand that you get. Just get pin and voltage-compatible RAM. As long the RAM type (just as an example: 262,144 x 8 bit) matches between the old and the new, you shouldn't have any problems.
 
This is where I get lost. Truthfully, I don't know the first thing about chips, especially when it comes to the stats that matter. Is there a site online that's a "one stop shop" for learning stuff like this, or do you just acquire the knowledge over time?

That said, would these work?
Screenshot_20230314_152045_eBay.jpg
 
Noted. How about these? It says FK60L instead of NK60L on the chip, but all else is the same. So far, I have not found any chips that match the model number exactly; this is the closest match.


Screenshot_20230314_154931_eBay.jpg


Thank you all for helping me. For someone who has very little experience with chips, y'all's guidance has been most appreciated.
 
It's unfortunate that no datasheet seems to be available for the NK variant chip.

I'd say that they'd probably work, but there's no guarantee that they will work. The only thing you can do is try them.
 
What’s the model number of the LCD? Looks like a Sharp LQ9D01A, same panel used in the PowerBook 180c.
 
I might just pull the chips off the original power/VGA board. It's unfortunate because I wanted to diagnose why that board never fired up. I guess I won't be doing that any time soon. Still, at least I'll have identical chips; at this juncture, that's what matters.

I am 99% sure that's what the label said re: LCD model number. I can't look now, as I have it all bundled up again. Still, I glanced at it enough to have reasonable confidence in that being the display.
 
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