Internal memory upgrade?

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Pr0f
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Internal memory upgrade?

Postby Pr0f » Tue Feb 13, 2018 10:16 pm

Picked up a QL on ebay, was going to be a reference machine for some current project work on the DIY QL.

Opened it up to have a looksee inside and came across this little lot:


Seems the HM50256 is a 256Kx1 DRAM chip...
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Martin_Head
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Re: Internal memory upgrade?

Postby Martin_Head » Wed Feb 14, 2018 11:06 am

I remember this was a service that someone supplied. It had a disadvantage, that the RAM expansion ran a bit slower than an external RAM expansion, because it shared the video memory.

I like the spaghetti by the clock crystal.


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Pr0f
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Re: Internal memory upgrade?

Postby Pr0f » Wed Feb 14, 2018 11:19 am

Martin_Head wrote:I remember this was a service that someone supplied. It had a disadvantage, that the RAM expansion ran a bit slower than an external RAM expansion, because it shared the video memory.

I like the spaghetti by the clock crystal.


It looks a bit heath robinson, but the soldering is to a good standard at least, but very prototype feel with the soldered wire wrap techniques and bent pins to a 'bus bar' approach.

I would image the performance suffers as you say, because this is using the video chip to do refresh I would imagine. I am tempted to unpick it all and return this to a relatively standard build, It apparently suffers from 'black screen' issue, but I haven't powered it on yet. Also one of the keyboard tails has sadly been snapped off, so I will probably have to replace that too. And with no power pack, I need to at least feed this thing with 9V, I can get by without the 15 AC feed at the moment, just for testing it.

Any ideas who supplied these - I have found details of the spem board with the 512K ram expansion, but that used a GAL for the logic and the board plugs into where the zx8301 normally sits, with that chip insterted into the corresponding socket on the spem board. It looks like there are 2 piggy back ttl chips up near the rom socket, and these presumably decode the upper address lines and provide CAS timing and the muxing for the A8 DRAM address line - these look like the only 2 lines not wired to the exising motherboad DRAMS


Martin_Head
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Re: Internal memory upgrade?

Postby Martin_Head » Wed Feb 14, 2018 11:29 am

I think you need +12v for the video circuitry. As for who did the upgrade, I think there used to be advert in the QL magazines.


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tofro
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Re: Internal memory upgrade?

Postby tofro » Wed Feb 14, 2018 11:54 am

Martin_Head wrote:I think you need +12v for the video circuitry. As for who did the upgrade, I think there used to be advert in the QL magazines.


12Volts should be needed only for Composite and Modulator. RGB should work fine without.

Tobias


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vanpeebles
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Re: Internal memory upgrade?

Postby vanpeebles » Wed Feb 14, 2018 12:08 pm

Pr0f wrote:
Martin_Head wrote:I remember this was a service that someone supplied. It had a disadvantage, that the RAM expansion ran a bit slower than an external RAM expansion, because it shared the video memory.

I like the spaghetti by the clock crystal.
I am tempted to unpick it all and return this to a relatively standard build, It apparently suffers from 'black screen' issue, but I haven't powered it on yet. Also one of the keyboard tails has sadly been snapped off, so I will probably have to replace that too.


I always think it's a shame to remove the upgrades on those old custom specials. It's a nice remember of how we used to live :) That would of been someones pride and joy :D


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Pr0f
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Re: Internal memory upgrade?

Postby Pr0f » Wed Feb 14, 2018 12:22 pm

vanpeebles wrote:
Pr0f wrote:
Martin_Head wrote:I remember this was a service that someone supplied. It had a disadvantage, that the RAM expansion ran a bit slower than an external RAM expansion, because it shared the video memory.

I like the spaghetti by the clock crystal.
I am tempted to unpick it all and return this to a relatively standard build, It apparently suffers from 'black screen' issue, but I haven't powered it on yet. Also one of the keyboard tails has sadly been snapped off, so I will probably have to replace that too.


I always think it's a shame to remove the upgrades on those old custom specials. It's a nice remember of how we used to live :) That would of been someones pride and joy :D


It would have been nice, but I do need a 'vanilla' ish QL to test some ideas on...

I may see if I can get it to work at least... I am suspecting the ZX8301 again in this machine, taken out by something unpleasant down the 8 pin din....


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janbredenbeek
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Re: Internal memory upgrade?

Postby janbredenbeek » Wed Feb 14, 2018 3:18 pm

Back in the mid-'80s, when memory upgrades were still expensive, there were two guys here in NL who sold such upgrades consisting of 16 256Kbit RAM chips and some extra logic for the address decoding (they used a PROM for that) and multiplexing. I even have the fitting instructions (which are unfortunately in Dutch). My first QL was modified like that (and in the process an extra serial port was added using an 6850 ACIA - I only needed 2400 baud at that time :D ). Look here for the result ;) . Of course this was not a mod for the novice tinkerer, but a lot cheaper than external memory upgrades (which were hard to get at from overseas anyway).

Earlier, I used a Micro Peripherals internal 256K RAM expansion which consisted of an add-on board placed onto the 8301 socket, with the 8301 again on top of it (much like the 8049 on various keyboard interfaces).

Both expansions were indeed as slow as unexpanded RAM, but at least Quill ran a lot smoother since it didn't have to dump half of its workspace to MDV as you were typing...

regards, Jan.



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