Spectrum +2B Issue 1 Rom Fault

[SpaceFlightOrange]

Hi.

Picked up a pristine +2B (Z70833 Issue 1) the other night, poly boxed, for £35. Unfortunately, it had a 48k PSU, but given the condition, it was worth a punt. Got it cleaned up and powered but after a brief flash of the copyright message, the screen turns to black with a white border.

I stuck my Smart Card V2 in and ran diagnostics, and everything checks out fine, apart from when I run the 128k rom test. Rom 0 & 1 both fail the test, 2 & 3 check out fine. I can load a 48k rom in fine, and run a little program, and running the 4.1 48k rom, I can load a game from the cassette player. Loading .tap files via the smart card works fine too.

I have no experience with these machines, but I assume roms 0 & 1 reside in rom chip A. My mate has left his with me so I can try out his roms (he has a +2B issue 2) but I'm a bit reluctant as I don't want to stick his rom in only for some other fault to kill his too! Is that even possible? I was going to lift the roms out of mine and try them in his, but havent gotten around to it yet.

I understand that I can use SST 27SF256 EEPROMs in this. is this correct?

[Guesser]

The first thing I would do is remove the ROM and put it back in, in case it's simply a bad connection in the socket.

[SpaceFlightOrange]

The first thing I would do is remove the ROM and put it back in, in case it's simply a bad connection in the socket.

Yeah, sorry. had tried this, but no change

[SpaceFlightOrange]

Update.

Did the old switcheroo with the ROMS.

Mine in the other +2B have the same issue. the ROMs from the other +2B in mine work fine.

Gonna take an image of them all and then when my EEProms arrive, I'll burn em.

[1024MAK]

I understand that I can use SST 27SF256 EEPROMs in this. is this correct?

I don’t know the specs of a SST 27SF256, so can’t answer your question.

However the ROM sockets in the +2B machines are compatible with 27256 and 27C256 EPROM chips. New windowed 27C256 (UV erasable” types are getting hard to find, but non-windowed OTP (one time programmable) types may be easier to get and as you will only be programming (burning) it once, that’s all that matters.

To program (burn) a 27256 and 27C256 EPROM chip, you do need an EPROM programmer.

Note that an EPROM is not the same as a EEPROM, and an EEPROM is not the same as a Flash ROM. Although they are all versions of similar technologies.

Some Flash ROMs and EEPROMs are mostly pin compatible with 27256 and 27C256 EPROM chips, but they are not always electrically compatible.

Mark

[1024MAK]

SST 27SF256 devices appear to have been discontinued many many years ago. Hence the only supply is used parts available on sites like eBay. Buying such chips is a risk, as you never know what you will get.

You may get genuine ‘pulls’ (real chips pulled out of previously working equipment).

Or you may get chips that have been cleaned, the pins re-tinned with shiny new solder, the original markings removed, and then new markings screen printed on them, so making them look like new chips. But you never know if the chip you get will actually be a 27SF256 or if it is some other chip. And of course, if it is not a 27SF256, it won’t program (burn)...

So I don’t recommend buying anything described as a 27SF256 unless you trust the seller.

Mark

[1024MAK]

27C256 OTP EPROM £1.11 + VAT + P&P.

Mark

[SpaceFlightOrange]

Thanks Mark for the reply. I got the info about the 27SF256 off the +3e ROMS page on world of spectrum here.

They are from a seller ive used before for obtaining 27128's for burning diagnostic ROMs for my Oric and Beeb. Never had any problems with them.

However, thanks for the link to the OTP chips. never thought of those. I'll order a couple and use the others for trying out different images.

[Ast A. Moore]

By the way, the +2B uses ROM version 4.1, not 4.0 like the +3. Keep that in mind.

[SpaceFlightOrange]

By the way, the +2B uses ROM version 4.1, not 4.0 like the +3. Keep that in mind.

Thanks. I've got them from Philip Kendall's site. They are supplied as 4 16k roms. Presumably I just need to concatinate image 0 & 1 for ROM A and image 2 & 3 for ROM B. Is this correct?

One thing i did want to do was grab an image of the original ROMs from my machine and my mates, for comparison, but Im struggling to find an ID for the chips to set on the Minipro.

I've done this with the Oric ROMs in the past, just by using a 27128 from the same vendor, but I'm not sure here. do you have any suggestions?

[1024MAK]

On your programmer select any 27C256 or 27256 device. But only read from it.

Mark

[1024MAK]

Guessers web site is also useful when it comes to the +2A, +2B, +3 etc... models, so go and visit the Spectrum section here

Mark

[SpaceFlightOrange]

Fantastic! Thanks Mark!

[SpaceFlightOrange]

Imaged the 2 ROMS, and there's 7 bytes different to the ROM-A image i've created from the individual images on Philip Kendalls site. ROM-B is identical.

[SpaceFlightOrange]

Thanks for the tip on the Proms from Farnell. Ordered a bunch. Just programmed one and its working great in the machine. Everything checks out.

[1024MAK]

Thanks for the tip on the Proms from Farnell. Ordered a bunch. Just programmed one and its working great in the machine. Everything checks out.

Mark