Spectrum Computing

That, but also because of how the ROM code detects how much RAM is present. The ROM is not testing to see how much working RAM there is, it's only testing to see how much RAM there is. This is an important distinction, as the test used assumes that all RAM that is present is fully working. The ROM c...

Adrian45 wrote: ↑Thu Feb 15, 2024 9:05 pm Just spent 20 min on Retroleum.co.uk , 16 items in my basket , went to pay and they only take paypal.

Have you tried contacting the site owner to ask about paying by credit card. He is normally very helpful.

Mark

Oh, and I feel that the small minority with an "80K" RAM upgrade are being left out :cry: Technically it is also possible to have a 32K Speccy (16K rubber key with 16K of expansion RAM). I don't know if anyone ever made expansion packs or fitted suitable DRAM chips internally for this thou...

Yeah but, no, but... Are we speaking about "straight" AY sound chip data, music notation, samples or what? 6K bytes of AY sound chip music data <> as data for samples. Then there is the mass storage system being used. Real tape LOADing on a real ZX Spectrum is rather slower than being LOAD...

Last one I had was okay...


Mark

No problem.

It's a lot easier when a DRAM chip fails and produces a binary 1 regardless. When they produce 'random' outputs or bianry zeros, it's a bit more tricky.

Mark

And artists are often capricious people ;) They may draw some stuff that won't fit you from a coding point of view, as the others said. If you tell them to redraw it, they will get offended and leave. That's it, I'm done with this, I quit, you can finish this topic on your own... :twisted: Mark PS ...

strangely the speaker makes no sound when i connect the meter - still reads 39 ohm , the diaphram looks good , moves nicely - does not appear to be held up from vibrating , but no noise - can i put 5 volts into it ? Err, not if you want it to work after. Wire a 220Ω or similar resistor in series to...

So… I was doing some AY music for an upcoming game by @gabriele amore. The actual game is under 48k, so I figured I'd have over 80k for the music, since it can only play on 128k machines. :shock: Oi! My AY card for the rubber key / + Speccy says otherwise... :dance As this is a hobby, I went for op...

I will be replacing every cap in the machine Just the electros I presume? Apart from C5 to C8 I mentioned above, the ceramics don't normally cause any problems. took the speaker out , getting 39 ohms across the terminals , from reading , thats good Yes. Does it click if you tap a meter lead as you ...

I feel your pain. Buying items from abroad is now a right pain. The U.K. leaving the E.U. has not helped. The real problem is IMHO called VAT. But let's not get into politics. Else we will get into trouble (in this forum, talking politics is almost taboo). The owner of Retroleum is very helpful. But...

Tell ya what, here a link to the seller I recommend

Mark

Adrian45 wrote: ↑Wed Feb 14, 2024 5:55 pm its a 128K +2 B Mark

Opened it up and had a look - what I think are 4 ram chips , socketed

one of these work ?

Only if shoehorned in.. These are 64k X 4 bit types, hence the pin-out is not the same.

Mark

Post above edited.

So, I'm back :!: :P :lol: For a replacement chip, you either need a TMS4532 - 15NL3 (which are long out of production and nearly as rare as a live Dodo). Or a 4164 DRAM chip, preferable a Texas Instruments (TMS) one. Although various other makes will work as well. If you find any or intend to buy so...

Yes, different DRAM chips are used for 'lower' and 'upper' RAM. 4116 are not suitable to replace a upper DRAM chip.

Be back later, as the site is about to go off-line...

Mark

H2G2 detected

Mark

Thanks Mark, I believe using my multimeter I can identify the base so I will just use that as the reference point and hope for the best. Oh no, you don't get off that easy.... https://youtu.be/nCryJU2sh3c?si=olLFSk2XCuEBt19D https://i.postimg.cc/Y4Nmqy8T/IMG-7800.jpg https://i.postimg.cc/c6hMc6RP/I...

I'll get a real one out later and take a photo.

Mark

the replacement must either be the exact correct 32K DRAM chip. Or a 64K DRAM chip that has the same row/address layout.

Mark

So, the reason for those test values is because we really want four different binary test patterns. With the RAM in a Spectrum, it's divided into the 'lower' RAM and the 'extension' or 'upper' RAM. The 'lower' RAM runs from 16384 (0x4000) to 32767 (0x7FFF). The 'upper' RAM runs from 32768 (0x8000) t...

It's a hang over from the ZX80 (which only had a 4K byte ROM). The ZX81 ROM built on the ZX80 ROM (now 8K bytes in size). Then the ZX Spectrum ROM is a development of the ZX81 ROM... Sinclair wanted maximum features for lowest cost (read keep something that worked, and make everything fit in only 16...

Here's a circuit simulation. Because it does not include a potentiometer, I've used a fixed resistor. Also not included is a LDR, so I have used a clickable logic level input (swaps between L and H) a diode and a fixed resistor. This very crudly simulates day/night as if there was a LDR. https://www...

Let's play spot the difference! Front cover #1 https://i.postimg.cc/fJMrGVvq/IMG-7768.jpg Front cover #2 https://i.postimg.cc/KKrFcVRr/IMG-7769.jpg So which is for the +2 (grey) and which is for the +2A / +2B? Maybe a side view would help... https://i.postimg.cc/CBBNsykb/IMG-7775.jpg Okay, I'll open...

For the 128K, the +2 (grey) manual is useful. It includes a big, big chunk of the original ZX Spectrum rubber key manual. Not to be confused with the later manual for the +2A/+2B machines which are different again.

Mark