Spectrum Computing

It may be that the problems with the keyboard existed before you opened the case. Were you able to test it before opening it? The keyboard uses a membrane, which itself is wired as a matrix of "switches". The "normal" keys (those that are the same as in a rubber key model) use a ...

With faults, I much prefer members to start a new topic. This saves confusion. However, I'm not an admin or moderator here.

Mark

So, just the few instructions needed to switch banks then I guess? I was expecting a bigger speed penalty to bank switching. The latch chip that stores the extra address bits for the memory is just as quick as the Z80. The limiting factors are what you have to do in your software routine and the OU...

I assume you were using an original Sinclair power supply unit (model UK1400 9V 1.4A). This is not a universal mains voltage type, as it requires a nominal 240V AC 50Hz mains input voltage. It will not produce enough output voltage if connected to a 110V – 120V 60Hz mains supply. The good news is th...

Yes, it has definitely been modified. The (phono) output connector on the modulator (what was the UHF TV output) will now output a composite video signal. I can't tell which version (there are more than four...) of the composite video modification has been done. If you want to know, you need to care...

Oh, and during the RAM check that the ROM does, it may be possible to check for some RAM faults that the ROM code does not test for. It's not possible to pick up all RAM faults, because the intention of the ROM routine is to simply work out how much RAM is fitted, NOT if it works correctly. Hence th...

Nice 8-) The next step would be an instruction trace, Often knowing at what point the Z80 is no longer executing the expected sequence can help identify the problem, or at least narrow it down. If there is no input from the user, the machine should make it to the "copyright" screen with th...

It's called bank switching or paging, but at the hardware level, the value on the data bus from the OUT is stored in a latch (register). Then some of the bits are used as extra address lines to the memory (ROM and RAM). The effect of this is that as described above, the Z80 can only see a "wind...

CP/M became a big thing and certainly helped make the Z80 successful. I don't know if during the design of the Z80 CP/M was considered. But it may have been. As far as I can recall, the 6502 did not have a direct equivalent to CP/M back then. There was FLEX for the 6800, and then later on a version ...

To be fair, the 6809 came along a lot later, and because it was late to the party, and hence not established (so not as cheap) only made it into a small number of computer models.

Yes, it was a good and powerful microprocessor.

Mark

This is probably more of a general Z80 question rather than applying to the Spectrum specifically, but do you think when Zilog designed and implemented the Z80's instructions and assigned them to either 1 or more byte opcodes that they always made the right choice? I'm not really talking about hypo...

For the game, see also
https://www.sinclairzxworld.com/viewtop ... f=11&t=289
and
https://www.sinclairzxworld.com/viewtop ... f=4&t=1317

For the details on how hires works, this site is a bit more readable (apart from the ASCII diagrams)

Mark

Sounds like a lack of volume issue.

Mark

That's diode D13 (1N4148).

Speakers unless the cone is damaged, either work normally or are completely broken.

Mark

And the last part of that post appears to have got lost. It should have ended:

'It will be hard to work out exactly what the problem is".

Mark

Okay, best if we calm down. Right, so there are some points I want to comment on. First off, we now know far more about how high speed digital signals are affected on PCBs now, compared to the 1980s. And Sinclair did have problems. Yes, the ZX Spectrum was okay, but the QL board had to be redesigned...

I'm curious to know whether the Spectrum can make use of a 2nd joystick button (or Master System pad buttons for example)? As Andy says, it depends on the actual joystick interface. By this, I mean both the type and the actual revision/version. This is especially relevant for Kempston or Kempston c...

You might be able to fit a composite connector to that monitor, it has markings for cvbs input, on a lot of those rebadged Philips (cm8833) monitors you can. Will not help if it lacks the PAL colour decoder circuitry... Does scart need voltage for it to switch? "Notice the +5 volts applied to ...

Although most TVs support composite video inputs on their SCART sockets, not all monitors do. So the first thing is to check any documentation for your monitor. The fact that you can get an monochrome red, green or blue image if you use one the red, green or blue RGB inputs without having to provide...

Thanks for reporting back

Have fun

Mark

Beware, the thinnest hair width solder splash can cause utter chaos...

Mark

Replacing IC14 is unlikely to make much, if any difference to the dot-crawl. The real problem is a design limitation. The 16K/48K/+ uses two different oscillators to produce the pixel clock and the colour sub-carrier/encoder. Hence they are not locked to each other. That's the problem (well, the mai...

Yeah, it's now okay

Will watch it later.

Mark

See also this topic.

Probably best to post any comments about this problem in the linked to topic rather than continue this topic.

Mark

The real problem here, is that many built in functions use the search even though the user or member may not be aware that said function is using the search system. For example, using the quick link 'active topics' (top left drop down menu) uses the search system. The second problem is that some oth...