Hardware detectives for FrankenQL?

[olifink]

I'd be interested in your opinions on the specimen in front of me right now... I've picked up a battered and bruised QL from eBay and upon opening found the following additions I'm not sure about. Obviously the previous owner is did a lot of DIY tweaking here (replacing the BT connectors with DSub9).

The first board sitting upside down on 2nd ROM socket I guess could be a homemade ROM to EPROM converter board?

Then - I'm not sure if IC25 (left to the ZX8302) was normally connected like this (ISSUE 6) on an additional socket with resistors soldered to it?

Finally there are then also prototype wires going from a chip soldered with some pins (others cut off) on top of IC19 (part no seems to have been scratched off) going to a soldered board with another two chips (almost unreadable again, one shows ti F8005, the other ti PHILIPPINES 428CR:

anybody able to venture a guess on what all these could be?

O

[martyn_hill]

Hi Oliver

Interesting! I can't readily decipher what that strip-board assembly is trying to accomplish, but the rest look like:

a) EPROM converter board - I agree. Interesting approach to mounting (its quite tricky trying to mount right-ways up in the space available, so I can see why the inverted mounting was chosen.)
b) That connection between the RS232 line driver and the HAL is curious and not a standard mod that I've ever seen. The connection itself is between the TX1 input to the line driver (driving SER1 TX) and the near-by ground pin of the HAL via a resistor. As the TX1 input is driven by the ZX8302, I guess the resistor is to provide a stronger pull-down to the output from ZX8302 - perhaps it was flaky or the modder observed a slow skew-rate and applied the mod to potentially create a sharper edge to the SER1 TX line.

I'll take a closer look at the picture of the strip-board connections - its probably just to repair a busted 2-4 (address) multiplexer.

[EDIT: I notice that the std 64kbit DRAM have been replaced by 256kbit devices, so that mod to the 2-4 address multiplexer plus the strip-board assembly is probably a home-brew internal memory upgrade.]

Does it power-up?

[olifink]

spot on - thanks. Yes, it does power on and takes longer than a normal QL during RAM check. The keyboard membrane was totally gone, so I had to borrow one from my home made GST 68k QL system quickly.

With that it does report a VERS$ as "JS" ROM and looking at SV.RAMT at peek_l(163872) gives me 655360 (640k) instead of 262144 (256k) on a normal QL.

Interesting indeed...

O

[mk79]

I've picked up a battered and bruised QL from eBay

Ah you bought that one I watched it, too, but because of the obvious hardware changes I refrained from bidding much Well, at least it's pretty unique...

[olifink]

Ah you bought that one I watched it, too, but because of the obvious hardware changes I refrained from bidding much Well, at least it's pretty unique...

Right, I wasn't expecting much as was more after the Germany PSU and the box of mdv cartridges were a nice addition. Some interesting things on there (so far I have only re-felted a few) I'm quite surprised that after that 30 years they do work surprisingly well. Good choice, Sinclair!

[Nasta]

It is a 'built in' mod to get 512k, which is why the original 64k x 1 DRAM pins have been replaced with 256k x 1, so it needs one more multiplexed address lines. I would be VERY interested in the way this was implemented because I don't see how it can reliably refresh the RAM...

[olifink]

I would be VERY interested in the way this was implemented because I don't see how it can reliably refresh the RAM...

I would try to untangle the wires and see where they lead, at least a couple go to the underside of the board... though I'm rather hesitant as - knowing me - I would trip up somewhere and probably kill that delicate creature...

I could send you the complete thing if you want...

[janbredenbeek]

It is a 'built in' mod to get 512k, which is why the original 64k x 1 DRAM pins have been replaced with 256k x 1, so it needs one more multiplexed address lines. I would be VERY interested in the way this was implemented because I don't see how it can reliably refresh the RAM...

It was a very popular mod here too in the mid-'80s. I even have the circuit diagram and fitting instructions somewhere, don't know it off-hand but IIRC it consisted of a PROM for the extra address decoding and an extra 74LS257 mux. I can post them if you like (but you'll probably need a bit of Google Translate since the instructions are in Dutch ).

Jan.

[Nasta]

Yes please!

[vanpeebles]

I love seeing those old home spun QLs, they look truly fascinating. And very Heath Robinson