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M5126 Macintosh Portable & MacEffects 8Mb Memory Expansion Screen STRANGE Backlight Flickering


New member
Hi all, 

First post here - I have been trying to restore a Macintosh Portable m5126 (backlit) model and I'm running into some problems when using the MacEffects 8Mb Memory Expansion card (https://maceffects.com/products/8mb-memory-upgrade-for-macintosh-portable-m5120-m5126). 

I have 3 memory cards total; the stock 3 MB (4MB?) card, and two MacEffects 8Mb Memory Expansion cards

So with the stock 4mb card, things seem to work just fine. Here's video to show it's working normally: https://youtu.be/3rL3qQXVArk

With one of the MacEffects 8Mb Memory Expansion cards, things work most of the time, except in certain situations, the backlight will flicker uncontrollably when triggered by certain software (so strange). Here's a video of the flickering card: https://youtu.be/1LRcpIBafWs - the flickering seems to occur when the RAM and or the hard drive are being read / written to. When I exit the program in the video, the screen goes back to normal (illuminated) but does flicker every 3 seconds or so. Restarting results in the card working again (until certain programs are loaded). 

Then with the other MacEffects 8Mb Memory Expansion card, I can’t boot successfully, with it always producing “bus error” messages. Here's a video of that card: https://youtu.be/z6e9smBmTxY

Both times when using the MacEffects 8Mb Memory Expansion card I have the jumper on limit 7 mb and hooked up with a jumper wire as instructed to the PDS slot. 

Has anybody that bought these cards? Is anyone else having problems with them, especially anything similar to what I mentioned above? The strangest part is that the 2 seemingly identical MacEffects 8Mb Memory Expansion cards are producing errors, but distinctly different from each other.

Let me know what you guys think. I took a very close look at the motherboard and it seems ok, and my recapping checks out, though I think someone might have tinkered with this particular unit in the past, so who knows what might be bad on the motherboard. I also tried the above tests using a scsi2sd and the original hard drive but both produce the same results. Initially I thought it was a voltage problem since the MacEffects guy mentioned that these new cards consume a bit more power than the stock card, but now I am not so sure. 

Basically, I want to narrow down the issue to the motherboard or the MacEffects 8Mb Memory Expansion cards. 

Any advise or ideas are appreciated!



Well-known member
Sounds like a power issue on the machine itself. Make sure you are using a known good power adapter (recapped, or replacement) and a fully charged battery. 

The cards must have the 7MB limit set so the machine sees a total of 8MB. Otherwise, it clashes with the address space that the backlight control resides on. You can also remove that jumper and place the original PC Pin jumper back on the card for testing, the unit will only see 5MB of RAM at this point but it will help rule out any issues that might be present in the upper address space. 

I have used them in my M5126 and I have not had an issue as of yet. 

I did notice the MacEffects version are using ultra bright LEDs. I am unsure of the current draw of these LEDs, whether they exceed what the system can give the unit. But a lot more people would be having this trouble. 

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New member
Hey Techknight thanks for getting back to me. The plot thickens, but I can rule out the cards as the issue, as the stock card is triggering the bus error now on boot as well. 

Though taking your advice, and setting up the cards for 5MB, it seems to work fine now, no boot problems and no flickering with that one working card in the 5 MB configuration, but the other card  that didn’t work in my fist post when configured for 5 MB won’t boot at all (just chime and nothing no bus error either) 

With all the examples in my previous post, the jumpers were set at the 7MB on position (pins one and two closed) with the jumper wire going from the right AS jumper pin to the rom slot pin 28. So that’s another mystery to why my unit was behaving like the 7MB cap was off (but only triggers the flickering when running programs like conflict catcher). 

The battery is new and the power supply was tested within voltage. The 9v battery is also new too. Runs for hours on the battery with the screen backlight on. I think maybe I might have a damaged IC or some other component somewhere that’s increasing the sensitivity to the power supply.

Do you think it’s salvageable? Any idea where to start looking on the system board for the culprit?