Spectrum Computing

Ok, so you think lower ram possibly. Does this mean you can rule out upper ram? Or could it still be upper ram? Also, if I was to get parts to make repairs and see where I get with it. Is there ways to test a chip when you remove it from the board? Thanks RPS At this stage, it looks like the ROM, t...

By connecting +5V to pin 5 on IC23, you are overriding the signal from elsewhere in the circuit.This point was deliberately chosen, as the existing signal comes via a resistor (R70) which limits the current flow so that the logic gate that feeds resistor R70 is not damaged. Pin 5 is an input to a lo...

Ast A. Moore wrote: ↑Sun Jun 17, 2018 8:02 pm

rps wrote: ↑Sun Jun 17, 2018 7:40 pm Do you know what number pin the +5v is on the IC23? Can’t find a pin diagram that shows it.

Pin 8 is V_DD, pin 16 is ground: http://pdf1.alldatasheet.com/datasheet- ... 4164B.html

Okay, how much beer have you drunk?

Mark

Hi, Do you know what number pin the +5v is on the IC23? Can’t find a pin diagram that shows it. On IC23 (a 74LS32, quad 2-input OR gates), pin 14 is Vcc (+5V). 0V/GND is on pin 7. I should point out that the method given in the earlier post about how to disable the 'upper' RAM only applies to issue...

The 'lower' RAM are 4116 DRAM (16k bits each) chips which run warm, with some running warmer than others. Sometimes when they fail, they may get hotter. But only if the supply can supply the extra power. Otherwise the switching transistor for the +12V and -5V dies. The 'upper' RAM are 32k bits each ...

Actually none :) By the way, by Beta 128 you mean Tr-Dos, right? Yes, except that TR-DOS is a, well, DOS —a disk operating system, whereas Beta (128) Disk is the name of the actual interface. Granted, the two were developed by the same company to work in tandem so are essentially synonymous in many...

Guesser wrote: ↑Fri Jun 15, 2018 3:52 pm Hmm, what if you use both 3" and 3.5" drives on a +3, would you vote for both?

"You may select up to 3 options"...
So yes, vote for both if you use both...

Mark

What floppy disk drive system do you own AND use? By use, I mean you actually use it regularly (more than twice a month) or occasionally (more than six times a year). Not that you have one and have used it a few times when it was new to you . I've listed the most common systems, but feel free to inc...

Before doing any further work on it, and certainly before replacing any chips, or cutting any chip legs, you should follow the instructions here over on World of Spectrum, to disable the upper RAM chips. Don't worry about oscilloscope tests that are also in that post. Disabling the upper RAM may all...

I gave some helpful hints to someone with a similar problem over on Sinclair ZX World in this thread

Mark

Controversial subjects do sometimes have this effect, especially if it's in the news or similar. With regards to the ZX Vega+. I'm not surprised, but it is very disappointing that bickering, fighting and what looks like deliberate sabotage, as well as possible incompetence has resulted in this outco...

Don't forget to replace C1, C2 and C9 before powering on (assuming that they have not been changed and are still the originals). These are all in the PSU.

Mark

That looks like it has lost it's serial number sticker (often a paper label). If coming from the U.K. with a U.K. 13A standard mains plug, it's most likely a U.K. spec. machine. There is plenty of help over on StarDot including how to convert a U.K. spec Beeb PSU to work on 110/120V mains. Mark

Richard (tricky) is currently working on a new Scramble demo/game for the Acorn BBC Micro. Here is a video he posted last month:
https://youtu.be/nMgHZjkSvJM
It's moved on a bit since then. He's not yet sure if he will develop it into a full game.

Mark

Seven.FFF wrote: ↑Thu Jun 07, 2018 2:07 pm That was a nice Defender.

I just picked up a model B on eBay, I’m stoked. Rare as hens teeth from US sellers.

U.K. model, USA model, or German model?

Mark

Jam and banana for me.

In white bread of course

Here's one link
And another...

And what is this wedding that you speak of? On second thoughts, don't bother, I'd rather not know. Blooming soap operas...!

Type the names / manufacturer names into a search engine... Search for pictures...

Mark

Mark

On any system, the Motorola 6845 CRT controller (which was also available from other semiconductor manufacturers) ONLY provides timing signals and address control lines for screen memory control. It has nothing to do with pixel data. Other circuitry has to be provided to generate the pixel informati...

Do you have, or have access to a logic probe or an oscilloscope, or maybe a logic analyser?

If yes, then it should be possible to determine if the system is trying to write data to the AY chip.

If you have a multimeter, you can test the power supply pins of the AY chip.

Mark

Not sure how quickly data in the workspace gets overwritten, but if using string functions does use the workspace, you may need to use PEEK and POKE to copy the data somewhere else (I'm assuming that simple functions and commands do not need to use the workspace). Of course using a small bit of mach...

Are you asking if BASIC can access this information, if machine code can get it, or if the information can be got from an emulator?

Mark

Yes, machine code in non-contended RAM will always be faster on a ZX Spectrum than a ZX81 running in FAST mode. Hence why in my original post I worded it very carefully. With machine code in, or using contended RAM, it very much depends on what it is doing and when it it doing it (compared to where ...