Yes, an ATmega328P is just two bucks. You need an ISP programmer (3 bucks) or an Arduino with the ISP sketch. k and m-firmware work fine with old tester versions.
Thanks a lot for your informations. I got a friend that could help me with the programmer... let's see.
Another question: I bought another tester as a gift for a friend, but when I opened the package I found a broken display and the seller has sent me a refund. I'm trying to find a new display: the old looks like an ST7565, but the flat cable has just 12 pins, while the similar displays on eBay and Ali have much larger connectors, with 18 pins or more. Any suggestions are welcome... Many thanks.
Probably the cheapest source I've seen mentioned for displays (they are also one of the larger sellers of displays on eBay if you would like to pay a little more for the same thing there)
http://www.buydisplay.com/This is a search for ST7565 based displays:
http://www.buydisplay.com/default/graphic-display?cotroller_ic=445Tutorial on ST7565's from a reputable source:
http://www.ladyada.net/learn/lcd/st7565.html If you really really want to replace the display exactly, it's probably more simple to just buy the whole clone again. Most of the displays sold come with breakout boards so that people don't need to solder ribbon cables directly. However, IIRC, AliExpress had some sellers listing overpriced components specifically listed as "Transistor Tester replacement [x, y, z]." They usually use whatever hair-brain-idiot brand name they made up to sell a clone (hiland, kkmoon, etc.). These names have absolutely zero meaningful value. Others have had issues with the same unit as you and have posted information. Watch the indexes I created and posted on the last page or 2 of this thread to find this information visually.
As an inexperienced hobbyist myself, I would attack this replacement display issue from a different perspective. Simply look at the issue from the perspective of someone that is building the device from scratch. Look at the documentation on the official PDF and add any display you like. Simply trace out and note the pinout you already have on your PCB and match it to the documentation then pick a matching display or solder wires yourself to add whatever you want. The makefile (a page that walks you through all of the code options step by step) will help you figure everything out to configure the code to match any display options with a supported controller (see official PDF).
I have been through almost every bit of documentation for this project on all of the different forums. Of all the displays I've seen, I would probably chose one of the NT7108 based units, I haven't had one in my hands but they look huge. The color stuff seems rather silly if you get a chance to see how slow the MCU is at clearing the screen. I plan to record this in a video at some point while comparing the speed with 8, 16, and 20mhz xtals.