Is it evil to downgrade a Spectrum...?

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
Post Reply
Firefox

Is it evil to downgrade a Spectrum...?

Post by Firefox »

It'd be really handy if I had a 16k Spectrum to assist in my hardware tinkerings, but they're much rarer than 48k Spectrums and perversely always seem to fetch a way higher price on ebay and other such sites...

Fellow Specchums, do you think the gods of retrocomputing would be displeased if I purchased another 48k Spectrum and gently downgraded it into a 16k?
User avatar
R-Tape
Site Admin
Posts: 6353
Joined: Thu Nov 09, 2017 11:46 am

Re: Is it evil to downgrade a Spectrum...?

Post by R-Tape »

Pervert.
User avatar
Ast A. Moore
Rick Dangerous
Posts: 2640
Joined: Mon Nov 13, 2017 3:16 pm

Re: Is it evil to downgrade a Spectrum...?

Post by Ast A. Moore »

Okay, admins, that’s an immediate ban. :evil:

:D
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
User avatar
Morkin
Bugaboo
Posts: 3251
Joined: Mon Nov 13, 2017 8:50 am
Location: Bristol, UK

Re: Is it evil to downgrade a Spectrum...?

Post by Morkin »

Image
My Speccy site: thirdharmoniser.com
User avatar
1024MAK
Bugaboo
Posts: 3104
Joined: Wed Nov 15, 2017 2:52 pm
Location: Sunny Somerset in the U.K. in Europe

Re: Is it evil to downgrade a Spectrum...?

Post by 1024MAK »

You do know that a simple BASIC command can reconfigure BASIC to think it’s only a 16K machine?

This won’t affect machine code programs. To fool these, a simple circuit made up of wire and a low power SPST (on/off) switch is all that is needed for issue 2 to issue 4S boards.

I don’t recommend trying to downgrade an issue 5 or issue 6A board.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
Looking forward to summer later in the year.
Firefox

Re: Is it evil to downgrade a Spectrum...?

Post by Firefox »

Well, the feeling in the room seems to be that it would be sacre.. sacril... wrong. :D
1024MAK wrote: Fri Mar 27, 2020 10:22 am You do know that a simple BASIC command can reconfigure BASIC to think it’s only a 16K machine?
Oh, I'm talking about tinkering together projects that plug into the back. The upper RAM's a bit in the way if I want to memory-map stuff.

Well, I suppose I could just use the ROMCS pin to drop the built-in ROM out temporarily. That'll make a nice bit of space in the memory map. I don't particularly need BASIC for my tinkering...

Back to patiently watching ebay. :)
User avatar
Alessandro
Dynamite Dan
Posts: 1908
Joined: Wed Nov 15, 2017 11:10 am
Location: Messina, Italy
Contact:

Re: Is it evil to downgrade a Spectrum...?

Post by Alessandro »

I have a boxed, almost mint 16K in my collection. I don't remember exactly how much did it cost me on ebay, but it was not more than a common 48K.

Are they really sought after so much?
Firefox

Re: Is it evil to downgrade a Spectrum...?

Post by Firefox »

Alessandro wrote: Fri Mar 27, 2020 10:44 pm Are they really sought after so much?
I don't know... It could just be the ones I've seen happened to have an inflated price.

I think they're pretty rare, though - I imagine a lot of them would've been upgraded, and after the Spectrum prices were slashed a year after launch or whatever I think most people would've said to themselves, "Might as well pay a few notes more and have the 48k version."
User avatar
1024MAK
Bugaboo
Posts: 3104
Joined: Wed Nov 15, 2017 2:52 pm
Location: Sunny Somerset in the U.K. in Europe

Re: Is it evil to downgrade a Spectrum...?

Post by 1024MAK »

Everyone including Sinclair were rather surprised that the 48K model was flying off the shelves far quicker than the 16K model even in the first year. So the 48K model is by far, the more common version.

Add in people upgrading, and although not rare, 16K models are not easily found. Hence they are relatively expensive on eBay.

@Firefox, there are over 128 free ‘8 bit addressed’ I/O port addresses to play with. More if you use 16 bit address decoding. Or are you intending to memory map something?

If yes, you can always use the ROM area as you suggested. Put +5V on the ROMCS and the ROM disappears from the memory map.

For issue 2 to 4S boards, to disable the "upper" 32k of RAM, take a piece of wire and connect pin 5 on IC23 (a 74LS32) to +5V. (link).

If you wire an SPST on/off switch in series you can enable it or disable it as you see fit. You can even wire in a LED to show the current status.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
Looking forward to summer later in the year.
User avatar
patters
Manic Miner
Posts: 467
Joined: Thu Apr 11, 2019 1:06 am

Re: Is it evil to downgrade a Spectrum...?

Post by patters »

I had a 16K issue 2 from my childhood and in about 2006 it died as I tried to upgrade it to 48K. I sent it to some bloke on WoS who offered to fix it, and who then immediately stopped answering PMs and stole it basically. I had even sent him a donor 48K Plus I had bought on eBay as well. And I could see he was still active on the forum. Bit of a shame really.

Fortunately for me I kept the perfect condition case from the 16K, so last year I got a very reasonably priced refurbed 48K issue 2 motherboard from Retroleum and managed to replace the keyboard membrane without damaging the original plate.
Firefox

Re: Is it evil to downgrade a Spectrum...?

Post by Firefox »

1024MAK wrote: Sat Mar 28, 2020 4:39 pm @Firefox, there are over 128 free ‘8 bit addressed’ I/O port addresses to play with. More if you use 16 bit address decoding. Or are you intending to memory map something?[mention]Firefox[/mention]
Yeah, I want to map actual memory...
1024MAK wrote: Sat Mar 28, 2020 4:39 pm For issue 2 to 4S boards, to disable the "upper" 32k of RAM, take a piece of wire and connect pin 5 on IC23 (a 74LS32) to +5V. (link).

If you wire an SPST on/off switch in series you can enable it or disable it as you see fit. You can even wire in a LED to show the current status.
Ah! By "downgrading", I was meaning to desolder IC23 and replace it with a socket, so I could put the IC back (for a 48k Spectrum) or put a low-profile socket with pull-up (a) resistor(s) soldered across it in instead (for a 16k Spectrum). But that's even easier!

Thanks very much for the tip! :)
User avatar
1024MAK
Bugaboo
Posts: 3104
Joined: Wed Nov 15, 2017 2:52 pm
Location: Sunny Somerset in the U.K. in Europe

Re: Is it evil to downgrade a Spectrum...?

Post by 1024MAK »

Glad I could help.

Do however double, nay, triple check that you have the correct pin on the correct chip, otherwise it could be carnage!

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
Looking forward to summer later in the year.
User avatar
beanz
Microbot
Posts: 183
Joined: Wed Mar 21, 2018 1:10 pm
Location: Texas USA

Re: Is it evil to downgrade a Spectrum...?

Post by beanz »

I don't see an issue with it, the downgrade can always be re-upgraded.
User avatar
RMartins
Manic Miner
Posts: 776
Joined: Thu Nov 16, 2017 3:26 pm

Re: Is it evil to downgrade a Spectrum...?

Post by RMartins »

patters wrote: Sat Mar 28, 2020 7:03 pm I had a 16K issue 2 from my childhood and in about 2006 it died as I tried to upgrade it to 48K. e.
It appears that it didn't die.
What happened is that you killed it ! :evil: :lol:
User avatar
patters
Manic Miner
Posts: 467
Joined: Thu Apr 11, 2019 1:06 am

Re: Is it evil to downgrade a Spectrum...?

Post by patters »

I posted on WoS at the time that it would only load from tape for the first few minutes of being on then the ULA would get hot enough to burn your finger on. The upgrade stuff didn't cause that. Then it failed completely.
User avatar
RMartins
Manic Miner
Posts: 776
Joined: Thu Nov 16, 2017 3:26 pm

Re: Is it evil to downgrade a Spectrum...?

Post by RMartins »

patters wrote: Fri Apr 03, 2020 12:53 am I posted on WoS at the time that it would only load from tape for the first few minutes of being on then the ULA would get hot enough to burn your finger on. The upgrade stuff didn't cause that. Then it failed completely.
You didn't need to justify yourself, I was just joking. :D

But anyway, the process of upgrading it, since it usually requires soldering of at least the extra sockets, might leave you with the uncertainty of having left some tiny bit of solder, somewhere where it shouldn't be.
And I can assure you this can happen without much effort, specially, if you had to de-solder or re-solder any contact, where you used a manual solder pump for example.

That tiny bit of solder can create some sort of short or intermittent short, that can and will probably lead to something being burned by over heating, since a short usually implies a stronger current somewhere.
User avatar
1bvl109
Dizzy
Posts: 98
Joined: Tue Jun 04, 2019 9:00 pm

Re: Is it evil to downgrade a Spectrum...?

Post by 1bvl109 »

1024MAK wrote: Sat Mar 28, 2020 4:39 pm Everyone ...
Well, maybe except those who owned an 81 with a wuhuhuoooOoobly 16k pack.
"Truth would quickly cease to be stranger than fiction, once we got used to it." - H.L. Mencken
Post Reply