Sinclair ZX80 / ZX81 / Z88 Forums

I can't found a good proven replacement for TR7 about the loud speaker.. I wonder if the C635 I used to replace TR4 would work? I don't even know if it will last as TR4.. I had to cross its leads but gave me 12V rail up again.. Another question is if this replacement can be the cause of bad quality...

The ZX81 (and ZX Spectrum) ROM code is designed to drive the Sinclair ZX Printer. So to fully understand the system used, you really need to see how the ZX Printer works. The ZX Printer burns the conductive metal coating off the ‘paper’ as a stylus moves across the ‘paper’. The stylus is moved by a ...

Not having had time to read all the posts made today, and at the risk of answering questions that have already been answered, nevertheless, I shall give my answers... :mrgreen: I own a multimeter which I can put in "20v DC" as you request, but it's not clear to me how to do the tests you are request...

Better late than never, even if it’s not a video but instead some static photos... Please note that this is an issue 1 board and is a bit different to the later board versions. However, the DC input connector, the modulator and the 4116 (or equivalent, in this case they are NEC D416C DRAM chips) ‘lo...

@Erm, so who was taking the photo? You are making a lot of assumptions...!

Mark

To go from mono to stereo, connect both channels together in the stereo plug. Make sure you attach a label saying “both channels linked together”. To go from a two channel (stereo) plug to mono, connect to the left channel only in the stereo plug and wire to the mono plug. The 0V/GND/screen obviousl...

I did not have time at the weekend to make a video. I will try to find time this week...

Mark

Here is a photo showing a stereo 3.5mm jack plug sitting on top of one of the ZX81’s 3.5mm mono jack sockets. In this case the 9V DC input, but all three (DC input, Ear and Mic) are all the same type. 942BBCD7-1601-4248-B1CB-273457467C71.jpeg As you can see, the 0V/GND connections do not line up :( ...

Also, the supplier I linked to for this: “ROM EL-2364 FLASH EPROM Chips (replacement for 2364 ROM)”. He can arrange to program it for you if you wish. He does charge extra for this service, check with him for the cost.

Mark

Oh, I forgot to say, if the Z80 CPU never executes a HALT instruction, the HALT pin will stay high. The code in the ROM does contain a HALT instruction.

Mark