Ast A. Moore wrote: ↑Thu Feb 06, 2020 5:37 pm
Very few +2B boards were fitted into casings with “+2B” actually molded on the bottom. Almost all of them were Issue 4 boards, and of those, most—if not all—were sold in Spain, as far as I know. I guess Amstrad just had a pretty pile of the original cases and didn’t feel like throwing them away just because of a new board revision.
There's loads of UK Issue 4 +2Bs (I don't have numbers but they're not uncommon based on what pops up on facebook etc), it's Z70830s in +2A cases that are rare and only seem to show up from Spain (those and the +3Bs).
Well, I’ll be. I knew the +3Bs were rare, and never encountered an Issue 4 +2B board myself. From what I read, I concluded that they were as rare as the bottom cases with the “+2B” molded on them.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
I was away for the weekend but I kept pondering on it and since everything seems to check out so far I'm wondering if one of the ROMs is bad. Considering they seem near impossible to find/too expensive I was wondering if it would be possible to burn my own.
I found some 27C256-150 EPROMs which seem to match the pinout of the speccy ROMs and I've been looking for an excuse to get an EPROM burner for a while so if that's possible to do then it would be a pretty cheap thing to rule out excluding the cost of the burner.
walde123 wrote: ↑Tue Feb 11, 2020 1:04 pm
Considering they seem near impossible to find/too expensive I was wondering if it would be possible to burn my own.
I found some 27C256-150 EPROMs which seem to match the pinout of the speccy ROMs and I've been looking for an excuse to get an EPROM burner for a while so if that's possible to do then it would be a pretty cheap thing to rule out excluding the cost of the burner.
Not only is it possible, it’s also incredibly easy, if you have the right tools. Have a look at the beginning of this thread for more info.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
walde123 wrote: ↑Tue Feb 11, 2020 1:04 pm
Considering they seem near impossible to find/too expensive I was wondering if it would be possible to burn my own.
I found some 27C256-150 EPROMs which seem to match the pinout of the speccy ROMs and I've been looking for an excuse to get an EPROM burner for a while so if that's possible to do then it would be a pretty cheap thing to rule out excluding the cost of the burner.
Not only is it possible, it’s also incredibly easy, if you have the right tools. Have a look at the beginning of this thread for more info.
Well, in that case I'll see if I can make some. Unless someone has any other troubleshooting ideas I guess I'll have to wait for a burner to arrive until I can update on things
walde123 wrote: ↑Tue Feb 11, 2020 4:53 pm
Unless someone has any other troubleshooting ideas I guess I'll have to wait for a burner to arrive until I can update on things
Does the machine pass the RAM test every time now?
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Some time has passed and I've got my hands on a TL866-II plus EPROM programmer. I haven't got any replacement EPROMs yet but I tried reading the ROMs from the Speccy and since it seemed to fail detecting PIN 1 which apparently is not connected in the ROM so I bypassed the pin detection and ID check and was able to get the contents of the 40093U ROM and the first half of it matches perfectly to the +2A/+3 v4.1 ROM 2 (+3DOS) found on here: http://www.shadowmagic.org.uk/spectrum/roms.html
I'm going to assume the other half of the ROM is fine too since the first half checked out but when I tried reading the 40092U ROM it just gives straight 0s, using the exact same settings as for the 40093 with simply swapping the chip in the socket in between attempts, so seems like to me that the 40092 is toast? or maybe I'm missing something. Anyway, I guess now I'll need to wait for the EPROMs to arrive so I can burn a replacement, I'm guessing there's some pin modification to do as well for using the EPROM since they expect 5V on pin 1?
To read the ROM chips from these machines, it’s best to manually select any brand/make of 27C256 EPROM. But only try to read from it, never try to write/burn to it.
Each of the two physical ROM chips contain two 16k byte ROM images. To see the other ROM image, get your programmer to read from 0x8000 (32768) onwards.
Just to add to what Guesser said... A 27C256 or 27256 EPROM chip can directly replace a ROM chip in these machines. No wiring or other changes are needed.
Mark
Standby alert
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
1024MAK wrote: ↑Sat Mar 07, 2020 1:41 pm
To read the ROM chips from these machines, it’s best to manually select any brand/make of 27C256 EPROM. But only try to read from it, never try to write/burn to it.
Each of the two physical ROM chips contain two 16k byte ROM images. To see the other ROM image, get your programmer to read from 0x8000 (32768) onwards.
Just to add to what Guesser said... A 27C256 or 27256 EPROM chip can directly replace a ROM chip in these machines. No wiring or other changes are needed.
Mark
Yeah I figured that would be the case, the machine is alive now so in the end the 40092U was bad, really glad it wasn't anything worse since in the end I only lost a few euros on some ram chips with some spares, and the eprom was only a few cents excluding the fact that I had to spend 40€ on the eprom programmer. Huge thanks to you and everyone else who helped me out. Still need to actually see if it can do anything but the startup screen is definitely a huge improvement over the garbled mess