Chinesium Transistor tester repair (fail?)

This works, believe it or not

This is a post I’m writing mere minutes after completing the last bit (a rarity). Months back a friend bought one of those yellow chinese ‘component tester’ modules from ebay, at the time of writing they can be had for $12.85 USD OBO. It came with a broken screen so you could only see a portion of what was being displayed. He got a replacement, but I took the broken one and intended to buy a replacement LCD and fix it. I bought a replacement ST7565¬†breakout board for $6.99 USD. After much continuity testing and board tracing I came up with this pin layout for the pads the flex ribbon on the LCD used to be soldered to:

I traced the pins to ground, power through some diodes to drop the voltage, some caps, and PD0-PD4 on the atmega. This at least told me I was dealing with 4 data lines. I tried some naive wiring permutations but eventually I checked them with a scope to come up with the guesses of Data, Clock, Enable, and RS. After much more fussing I gave up and resorted to actually research the project that the chinese copied for clues. Here’s where I find all the information I needed.

from the master project document that shows lots of variations

First I find the hackaday article on someone converting the transistor tester into a display for his car (proving that this product is SO cheap that it’s the most economical way to buy this screen and microprocessor together. He has a schematic so I didn’t have to do all that tracing. Next I find this master document on the transistor tester that directly calls out the pins I need to connect because they all apparently use the same codebase (clone or otherwise). So I connect it up and….

um…

It’s backwards. According to the guy who ported this game thing to the transistor tester hardware you have to flip the Y direction for the screens used on these. Which means a normal screen is flipped when driven by one. Great. All that work and now it’s flipped. I also found out that apparently now I have to hold the button to make it work. I think there’s supposed to be a keepalive transistor (on PD6?) that the mcu can use to give itself power after the initial button press, and mine might be blown. I can probably trace that but now I’m stuck rebuilding the code and reflashing it to work with my screen. This was supposed to just be soldering some wires and boom! working unit.

One Response to “Chinesium Transistor tester repair (fail?)”

  1. Chinesium Transistor tester finished (not fail) | Evan's Techie-Blog Says:

    […] is a direct follow up to my completion of the repairs and modification of my cheap chinese component tester. When I last left off the display was wired […]

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