Sinclair ZX80 / ZX81 / Z88 Forums

That's why I asked if the Z80A was in a socket, as if it was, it would then be possible to test each multiplexer with a meter by removing the Z80A.It may still be possible but I need to check before posting details. Which means finding some time. Either a dual channel (or better yet, a four channel)...

It's not the composite video modification. Some ZX81 do suffer from with the top line of text slanting or the bottom line being partly distorted. You would get these symptoms if you were using the RF TV output. Which version is the ULA? If you don't know what to look for, post up a photo of it. The ...

Okay, well, at least it looks like there are no short circuits with the data lines to the 4116 DRAM chip data lines.

Mark

The voltages are good, so all the power supply circuitry is fine :D There may be a bit of variation between the resistance tests, on those results I would not suspect IC7 at this stage. Were these to tested the 0V/GND rail or to the +5V rail? I did ask that you test to each. Is IC2 (Z80A processor) ...

Given that you are going to be burning an EPROM anyway, the easiest way is to use a 16K byte (27128). Patch the BASIC part to jump to the ‘upper’ half, where you can have a short bit of code to copy your program into RAM and then set-up the BASIC system. Then jump to the main loop in the BASIC ROM w...

Err, RUN does a RESTORE 0 ...

Mark

Hello Jason Welcome :D I’ve moved your first post to this (ZX Spectrum BASIC) section of the forum. To attach a Z80 snapshot file, you will have to compress it into a zip file. Then attach that. As to the error, are there any READ keywords elsewhere in the program? The error report is saying that it...

After the voltage tests, next I suggest carefully removing all eight 4116 DRAM chips. With the power disconnected, use the resistance range to test between pin 2 of each 4116 socket and then to the 0V/GND rail, then again to the +5V rail. Record each result so that you can compare results. Which mul...

That four black/white vertical bar display can be caused by a number of things, such as power rail problems, RAM problems, multiplexer chip faults... The diagnosis ROM not running indicates that the processor is either not running or it's executing garbage. The later can occur if there is a short ci...

Before you replaced any capacitors, TR4 and TR5, did you do any voltage tests? Did you carry out any voltage tests after you renewed these? If the -5V supply was okay, it would be unusual for all eight 'lower' DRAM chips to all be faulty. If this board does not have the Sinclair DC/DC converter modi...