NEC — PC Engine LT
An epic of strife, perseverance and adaptation. The NEC PC Engine LT is the 1991 laptop-format PC Engine with a built-in colour LCD. Almost always dead from cap leakage. This one needed a full recap, a new voltage regulator, and an off-the-shelf voltage inverter module to replace the T500 LCD bias transformer, killed by the electrolyte. Without that, the screen stays dark.
6.5V regulator (M5291FP)
M5291FP-600C, a Mitsubishi (now Renesas) regulator in an SOP-8 package, marked 5291, sourced from UTSource. The 6.5V regulator that feeds the board's 5V regulator. It had quietly failed and was why the console stayed dead after the recap; replacing it brought back sound and backlight.
LCD bias module (T500 replacement)
NOYITO MC34063A inverting converter module, sourced from Amazon. It takes the board's +5V (its input range is +3.6V to +36V) and inverts it to the negative bias the LCD needs, adjustable from -1.5V to -36V on the onboard trimmer, standing in for the dead T500 transformer that the electrolyte killed. Small enough to tuck into the recess in the top shell.
Turbo Everdrive Pro
Turbo Everdrive Pro by Krikzz, the PC Engine flashcart used to run games during the LCD testing and diagnostics.
A while ago I acquired a PC Engine LT that would power on but do nothing at all. Today we'll have a look at why and at its journey to its final destination. Stay a while and listen.🧵👇 #pcengine #RETROGAMING #repair #restoration
As you can see, there was heavy electrolyte leakage on the board, near the 5V regulator and power input jack, even below the board. I start by wiping that off and by immediately deciding, I'd have to remove the HuCard slot and the Ext Bus connector.
Starting with the HuCard slot, as suspected there was leakage under it so I proceed to clean it. I also inspected the bottom part and there were signs of corrosion near the 6.5V regulator.
Removing the Ext Bus connector and the 5V regulator, it's much the same, heavy leakage all around. So I doused the board in white vinegar and let it sit for a while to neutralize the electrolyte.
Next I put the board through the ultrasonic cleaner. Also did the same with the bottom part of the shell because there was bound to have electrolyte there too. We end up with a fairly clean board and no visible broken traces that I could immediately tell.
After recapping the board, it's still no different than what it was before, so I soldered on and started to investigate.
After much probing and a fuse replacement later, I started to suspect the 6.5V regulator (M5291FP), so I removed it, inspected under it for broken traces but found none. So I ordered it and waited a fair bit, replaced that and tested.
There we go, this little part was preventing the console from coming alive as this regulator feeds the 5V one and it was not generating the 6.5V as it should. Now we have something to work one. We have sound and backlight but no picture, on the LCD. Onwards we march!
A lot of head scratching later I found out that the LCD needed a negative voltage on pin 10 of the LCD connector to allow the pixels to twist and allow light through. Turns out this is generated by T500 and it had one of the wires on the output side broken.
I knew I could repair it but I decided to try and remove the casing to get a better look. Turns out that was a really stupid idea... That destroyed the transformer there was still some goo inside so maybe it would fail long term if repaired. 🤷♂️
So next I decided to test if the screen would work with the voltage present, or if I had to replace it. Using my bench PSU and slowly dialing the voltage up, the screen came alive. So I began a quest to find a circuit that I could fit inside the shell to do this job.
After some trial and error I managed to find something that did just the trick and fits neatly into the recess on the top part of the shell. Finally my LT is working! This was one hell of a ride!
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