Spectrum Computing

The Z80 is fitted the wrong way round! On ZX81 issue one and issue three boards (an issue two board has never been seen as far as I know), all the chips are orientated the same way round, that is, with the edge-connector/expansion port furthest from you, they have pin 1 on the left. Note that the fa...

Hi. Unfortunately the short could be anywhere where the two lines are close to one another. Although if the Z80 or it’s socket has been worked on, that is the most likely place. Sinclair not using a solder resist layer on top of the board does not help… I presume you have tested using a multimeter o...

But are the photos of the same board version? Amstrad produced various versions. Some of the errors were corrected until the final version had no factory modifications and they eventually fixed the poor sound from the AY sound chip audio circuitry (although the +3s with this board version are R@RE i...

Did you try the ‘suspect’ chips from the ZX81 in the working TS1000? Did it still work? If yes, it proves the swapped chip is good. Can you post a photo of your ZX81 board please. A white screen normally means that the ULA is ‘okay’ (at least, it’s partially working) and hence the oscillator is also...

oO cozy Oo wrote: ↑Thu May 18, 2023 7:19 pm Thanks for that It looks a right bodge job

The factory workers would never have expected anyone to look at their work. It may look messy, but it’s functional.

Mark

The web site that describes Dylan's diagnostic software (as well as the hardware) is here . The LEDs flash in a sequence and at one point will indicate which bit in each byte is malfunctioning. With Dylan's hardware design, a user when running it as a diagnostic device, does not get to choose which ...

The diagnostic card/ROM should indicate which part of the memory is failing.

What did it report or show?

The lower DRAM is IC6 to IC13. Each DRAM chip supplies ONE bit in the eight bit BYTE.

Mark

Umm, there is some interest in Sinclair computers in Germany, as there is a german language forum https://forum.tlienhard.com/phpBB3/index.php

But yes, the increase in the hits to this site is very unlikely to be a sudden surge in people interested in old computers in Germany…

Mark

This one turned up, and I was so quick to buy a spare interface (to try with rotary encoders) that I didn't notice the odd connector. I did wonder about simply soldering an edge connector onto it, but I've noticed something else weird about it. The track connections are upside-down. The pins that a...

A photo of a version for the ZX81 (or ZX80) from Maplin is shown here

Mark

Back in the eighties, there were back planes / expansion boards, that had multiple (female) edge-connectors sockets soldered on. These allowed multiple expansion cards / interfaces to be plugged in. Hence some manufacturers supplied their expansion cards / interfaces with an edge-connector rather th...

LCD TV?

Some of the so called picture improvement settings for LCD TVs can affect the picture.

Mark

A photo of the problem helps ;) The composite modification that uses an electrolytic capacitor is generally considered to give better results than the version that just uses a wire. The capacitor enables the DC voltage level in the Spectrum to not upset the voltage level in an attached TV (the Spect...

I'd imagine the hardware to decide such a scheme would be massively more complex than simply having a definable palette of colours, as other machines did. Keep in mind when comparing complexity, a definable palette requires fast SRAM or registers inside the ULA, which eats up ULA resources. I do ag...

The programming manual for the ZX Spectrum is here . Some web pages describing the screen layout and how it’s display file is laid out are: http://www.breakintoprogram.co.uk/hardware/computers/zx-spectrum/screen-memory-layout https://www.overtakenbyevents.com/lets-talk-about-the-zx-specrum-screen-la...

Well, it depends… a ZX81 display file when fully expanded, is arranged in a more logical manner compared to the ZX Spectrum. Under BASIC, yes, the display file (the normal term for the area of screen memory on a ZX81) is a character based system. It’s actually 33 characters per line, but the last ch...

The loss of one, or even two RGB channels should not result in the screen you have. If there is a manual control for the SCART input, are there also any other controls or settings? Another question, does this TV have two SCART sockets? If yes, normally only one will be RGB input compatible. Mark

Please note, the post below was written before the OP posted their code. With a ZX Spectrum, there are more places to store machine code. And more importantly, this machine has a SAVE and LOAD commands that can save and load code. The ZX81 can only save and load BASIC programs. Hence small machine c...

Also keep in mind that really for the best stereo, you should have two AY chips. One for the left channel and one for the right channel… I can’t answer which is most common, ABC or ACB. But I believe the proportion varies between different countries. In the U.K. ABC may be more common than ACB. So t...

There have also been various expansion/interface cards that add a AY sound chip or other sound chip. Some of these have a stereo output.

Mark

If the through hole plating is no longer present, then I definitely recommend using wires. Making sure both the top and the bottom are soldered. Have a look at how I mounted a Recom type on a ZX81 using wires here . I did not use thermal paste or indeed anything else to hold the Recom. It is worth u...

If the +12V line was at 17V, then there is a very good chance that the +5V rail was also at a very wrong voltage.

Can you post a photo of your Traco TSR 1-2450 please.

The datasheet is here.

Mark

It is possible to damage interfaces via a static electric charge.

The divMMC Future really needs testing on another ZX Spectrum.

Mark

MrRomka the normal problem with modern TVs with SCART sockets, is that they have automatic signal selection via the two control inputs on the SCART socket (pins 8 and 16). If these don’t have the correct voltages, the TV defaults to composite video. This will not work properly for a lead wired up f...

Not wishing to derail the topic, but I can’t resist replying. My Facebook account was actually set up my one of my former workmates (only former because he left the company not because of any other reason) using a new email account also set up by him. Let me be clear, it was not done for any bad rea...