Hardware detectives for FrankenQL?

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olifink
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Hardware detectives for FrankenQL?

Post by 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?
IMG_20181117_131604.jpg
IMG_20181117_131556.jpg
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?
IMG_20181117_131659.jpg
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:
IMG_20181117_132030.jpg
IMG_20181117_131638.jpg
anybody able to venture a guess on what all these could be?

O


martyn_hill
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Re: Hardware detectives for FrankenQL?

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[EDIT: I notice that the std 64kbit DRAM have been replaced by 256kbit devices, so that mod to the 2-4 address multiplexer plus the strip-board assembly is probably a home-brew internal memory upgrade.]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

Post by 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


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mk79
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Re: Hardware detectives for FrankenQL?

Post by mk79 »

olifink wrote:I've picked up a battered and bruised QL from eBay
Ah you bought that one :D I watched it, too, but because of the obvious hardware changes I refrained from bidding much ;) Well, at least it's pretty unique...


olifink
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Re: Hardware detectives for FrankenQL?

Post by olifink »

mk79 wrote:Ah you bought that one :D 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! :D :o


Nasta
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Re: Hardware detectives for FrankenQL?

Post by 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
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Re: Hardware detectives for FrankenQL?

Post by olifink »

Nasta wrote: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...


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janbredenbeek
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Re: Hardware detectives for FrankenQL?

Post by janbredenbeek »

Nasta wrote: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
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Re: Hardware detectives for FrankenQL?

Post by Nasta »

Yes please! :)


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vanpeebles
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Re: Hardware detectives for FrankenQL?

Post by vanpeebles »

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


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