New QL user & owner

[MetroZodiac]

Hi all,

I have been emailing Vitaliy with regards to the tetroid interfaces. In particular I'm looking at the TDI interface, as this looks like a plug and play device (slots into the expansion port of the QL), so I would be able to preserve the originality of the QLs ROM, whilst allowing me to switch to the interface's minerva ROM and making use of the memory expansion. Also, having an SD card slot helps woth loading software instead of using the microdrives (which would be kept in place anyway, just not used).

He has expressed concerns however that it may not be compatible with the onboard 32k ROM (maybe it would rely on a minimum of 48k)?

What is everybodys thoughts on this?

[stephen_usher]

We don't know what changes Sinclair made between this prototype and the production machines. It's quite possible that it's not even binary compatible with changes having been made to the ZX830x designs.

[janbredenbeek]

That looks like it's an early development machine used internally within Sinclair. The date on the ROMs would be about a month after the announcement of the machine in the media but a few months before the dongle encrusted machines made it into people's hands.

I would be very surprised if the ROMs held a fully working copy of QDOS and SuperBASIC given how early they are.

Tony Tebby claimed in 2009/2010 that JM was ready by March 1984 (see QL Today archive) but early machines were shipped with older versions to mask hardware issues... strange story but lead times for ROMs were long and perhaps Sinclair had piles of EPROMs already programmed with FB/PM and erasing and re-programming would take too long?

[MetroZodiac]

Hi all,

The scart cable finally arrived today! However, plugging it all in, I either get a blue screen, or rarely a black garbled screen.

Also, if I press down gently on the microprocessor chip, I get a continuous single tone beep from the speaker. Any ideas?

[Chr$]

Hi all,

The scart cable finally arrived today! However, plugging it all in, I either get a blue screen, or rarely a black garbled screen.

Also, if I press down gently on the microprocessor chip, I get a continuous single tone beep from the speaker. Any ideas?

Have you removed the socketed chips, cleaned the sockets and re-seated them? Without spare known working chips to swap out and see if anything changes, there isn't really much you can do... apart from obviously chasing around with a 'scope, but having known working chips would probably save a lot of bother. A Minerva ROM could possibly help if there is a RAM problem, but it sounds like it could be more than that. At least it's some kind of screen though and not black, so that probably means the CLA2345/aka ZX8301 (next to the CPU) is ok.

Edit: I wonder if the colour is off and the blue screen is actually a green screen (which indicates a RAM problem). You could also try piggy backing known good RAM chips on each of the installed chips to see if that changes anything.

[MetroZodiac]

Yes I have removed all chips, cleaned the board and each chip with IPA and reseated; still getting the same problem. I'm wondering if its the ULA next to the 68000 chip, as Ive read this is responsible for video signals for RGB.

[Chr$]

Yes I have removed all chips, cleaned the board and each chip with IPA and reseated; still getting the same problem. I'm wondering if its the ULA next to the 68000 chip, as Ive read this is responsible for video signals for RGB.

When they fail you tend to just get a black screen and no video at all, so it might be ok.

[MetroZodiac]

With the blue screen, it looks fuzzy around the edges, so its almost like it tries to dusplay a picture.

I have removed each of the chips in turn, then powered on. Removing the ULA, rom chips and micro processor have an effect on the picture.

[Chr$]

I think personally my next step would be to check the content of those ROM chips and of course try a known working pair (or single 27512 type), written with a ROM of the full 48kb. Those 27128 chips are both only 16kb (as mentioned before) so it's possible it had an external ROM dongle originally, which is now missing.

Might not be that easy though, as one is labelled 0000 and the other 4000 (and the code from 8000 onwards 'was' external. Normally they are 0000 and 8000 internally. So I think would indicate that addressing might be different. Someone else will be able to offer a better insight.

[janbredenbeek]

With the upper 16K missing the RAM test should still work as this lies within the first 16K ROM. Given the fact that the test pattern doesn't appear, it looks like there is another hardware failure.