Spectrum Computing

dfzx

I have an issue 3 board which has a faulty 12V supply (reads a wobbly +1.2V). -5V works correctly. I've never tried to fix a DC-DC problem before, so I thought I'd start from first principles. The board has had a DC-DC mod of some sort, so I've had a good look at it and taken notes. Here's an annota...

dfzx

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 t...

dfzx

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 the only v...

dfzx

Whenever someone pops up asking for help with a broken Spectrum, the initial investigation asked of them is always the same: measure the voltages, tell us what test equipment you have, then do some initial signal checks based on what they can do with the equipment they have to hand. Would it not be ...

dfzx

If the QL had looked like Rick Dickinson's redefinition, it could have had the mechanism from a clockwork mouse inside it and it still would have flown off the shelves.

dfzx

chernandezba wrote: ↑Wed Feb 28, 2024 3:05 pm 2 Menus. "several screens" is exaggerated
...
Nothing further your honor

I found it complicated and confusing. Sarcastically dismiss the feedback if you like.

dfzx

I think you are exaggerating Are you really serious it’s difficult to get to the menu save screen? :oops: I'm not exaggerating. That STL screenshot took me about 10 minutes to make. Getting to the menu isn't difficult. Getting a screenshot of what I wanted proved very difficult. The problem is that...

dfzx

However, I think it should be possible to develop the module on a two-layer PCB, and the price difference here is significant. Earlier in the thread you said the price difference at JLCPCB between an order for 2 layer boards and 4 layer boards is about $5. Here in the UK that's less than the cost o...

dfzx

Here's one, screenshot from my slicer:

Very clever.

The option in ZEsarUX is all but impossible to use though, it took me ages to get that!

dfzx

That's a really nice piece of work, Tom, great job. I was thinking about making something similar to house my recreated ZX Spectrum Expansion System project, but there was a problem I couldn't see an easy answer to: the PCB for a project which is housed in such a case obviously needs an edge connect...

dfzx

You wait until you get tin whiskers. Then you'll be puzzled.

dfzx

They say that you can pay through paypal with a credit card if you log in as guest but I just cant see that option on my screen I'm pretty sure it means logging into Paypal as a guest. i.e. you don't need a Paypal account. So make your order at Retroleum, click to pay via Paypal, when the Paypal wi...

dfzx

Ah right, I suspected people were doing this unrolled. It just eats in to the RAM, but I think I've got enough space left, plus I can move some of the non-in game graphics in to low RAM. I can probably free up 2kb or so, and I'll give this a go... here is where I find out this is exactly how the co...

dfzx

Adrian45 wrote: ↑Sun Feb 11, 2024 8:50 pm SUCCESS !!!

Hurrah!

Adrian45 wrote: ↑Sun Feb 11, 2024 8:50 pm but no sound from spectrums speaker when game playing

OK, power up into BASIC and try

Code: Select all

BEEP 1,0

If you hear the tone from the internal speaker then it's clearly working. If not, that needs looking at as well.

dfzx

i dont think its volume ... im thinking it is a hardware issue - would old failing caps possibly effect the signal going into the machine Here's another thread on the topic on another site. Here's another . It isn't out of the question that a capacitor is causing a problem, there's a bit of filteri...

dfzx

Are you supposed to hear the noise of software loading from the spectrums internal speaker during loading ? Yes! The tape loader screeching noise is absolutely characteristic of the machine and you should be able to hear it as the tape loads. If you're not hearing that, you're missing out. So is th...

dfzx

There's a bit of information in this thread about volume and amplification and the options open to you. Probably other threads as well if you search the archives, it's quite a common subject. If you want to investigate your apparent upper memory issue I suggest you start a new thread with a suitable...

dfzx

Your machine is a 48K, the DRAM slots in the lower right are all populated. It sounds like it was sold to you as a 16K because the upper RAM isn't working? You might still be able to load a 16K game, though. What device are you using to play the tape? Spectrums require significant volume from the ta...

dfzx

That's really interesting, I've never heard of a CPU NOP tester...

dfzx

And, once past the 4-pixel position, ... And excuse my ignorance as well, please, what is the 4-pixel position? The original thread suddenly started talking about 4 pixels, which didn't make sense to me because attributes are aligned to 8 pixels. Hence I lost track of that discussion. But clearly 4...

dfzx

Some issue one and some early issue two boards have extra daughter boards to correct I/O contention issues. This was then incorporated in later issue ULAs. Some may have escaped modification... Is that what's going on here ? I noticed that auction yesterday, and was rather surprised to see an uncas...

dfzx

PROSM wrote: ↑Tue Jan 30, 2024 11:53 am again, this has been a fruitless endeavour.

Nevertheless, I am in utter awe of your audio signal preprocessing abilities...

dfzx

SkoolKid wrote: ↑Fri Jan 26, 2024 11:50 am And now I have an import duty/customs clearance bill of over $100 to pay before I can receive the package.

You would have always expected that, though, would you not?

dfzx

Many thanks for all the help. I'm using an RP2040 attached to the edge connector to sample signals and understand what's going on with the CLK line. Nothing is taking over the machine, and the Spectrum isn't expected to be doing anything useful while I conduct these experiments. I was seeing odd val...

dfzx

Thanks Mark. Unfortunately, in my attempt at brevity, I didn't quite ask the question I wanted to, which was this: If I assert the Z80's /RESET pin (via a device on the Spectrum's edge connector), and hold that /RESET pin asserted , am I guaranteed that memory contention will never happen and the UL...

Spectrum Computing

Search found 677 matches

DC-DC mod query

Re: Hardware diagnostics interface (Pico based)

Re: Hardware diagnostics interface (Pico based)

Hardware diagnostics interface (Pico based)

Re: Sinclair QL Design issues

Re: ZEsarUX 11 Beta

Re: ZEsarUX 11 Beta

Re: New open lower RAM module design (photoessay)

Re: ZEsarUX 11 Beta

Re: Replacement Case for Interface 1

Re: Recap Problem.

Re: Who do you buy your spare parts from

Re: Beating the C compiler...

Re: Cant load anything

Re: Cant load anything

Re: Cant load anything

Re: Cant load anything

Re: Cant load anything

Re: Contended memory with the Z80 in reset

Re: Another ATTRibute scroller, But At Pixel Speeds

Re: Timing differences between different versions of 48K ULAs?

Re: ZX Spectrum code on The IT Crowd DVD ?

Re: ROTW units shipping soon

Re: Contended memory with the Z80 in reset

Re: Contended memory with the Z80 in reset