Attic 81's - My collection and attempts to repair

Discussions about Sinclair ZX80 and ZX81 Hardware
Moggy
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Re: Attic 81's - My collection and attempts to repair

Post by Moggy »

1024MAK wrote: Sun Jan 03, 2021 9:13 pm Any of the cheap Chinese programmers will program (blow) a 27C64, or a 27C128 EPROM. But note that they are unlikely to be able to program the older 2764 or 27128 EPROMs, as these normally require a 21V programming supply. All of these EPROMs are obsolete.



Mark
I thought I'd already said that :?

Obsolete but still available albeit used.If one just wants something guaranteed then yep buy new but for us old dabblers theres nothing like the smell of a shorted EPROM in the morning. :lol:
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1024MAK
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Re: Attic 81's - My collection and attempts to repair

Post by 1024MAK »

You did :lol:

Maybe my brain is in slow mode :lol:

This is the ROM image that I’m gonna be using 8-)

Mark
Moggy
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Re: Attic 81's - My collection and attempts to repair

Post by Moggy »

All my zeddies have this ROM image, Mark and it is bloody fast BASIC wise in a lot of cases the MC obviously stays the same, the no screen flicker pause is useful no more FOR NEXT loops needed anymore.
The SQR function is supposed to be quicker so for my own test I printed a screen full of the SQR PI using the ZXpand ROM which took about 1 min 10 sec and using the big bang ROM took 8 seconds!

Also try some of Andre Baunes BASIC games and see the difference.
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Paul
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Re: Attic 81's - My collection and attempts to repair

Post by Paul »

1024MAK wrote: Sun Jan 03, 2021 9:13 pm
I’m going to blow a chip with the latest version of the BASIC ROM later this month. When I do, I will document it in a new topic. I’ve not decided which chip to use yet, other than it will be a 32k byte type (so either a OTP 27C256 or a 28C256).

Mark
Hi Mark, I use Winbond W27C256. They are EEproms but 100% pin compatible to 27C256 so easier to adapt than AT28C256 and electrical erasable. No need for UV stuff. 50pcs normally below 25€ including postage.
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sheddyian
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Re: Attic 81's - My collection and attempts to repair

Post by sheddyian »

1024MAK wrote: Sun Jan 03, 2021 8:38 pm Why Wait - see this topic ;)

Mark
Thanks, I'll order a few of those transistors and try it out on at least one of my Zeddys.

Ian
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Re: Attic 81's - My collection and attempts to repair

Post by sheddyian »

Thanks for all the replies and info about ROMS/EPROMS/EEPROMS.

I think it's a medium term project given the extra cost that I'd rather not spend at the moment, but I'll keep an eye on ebay for cheap EPROM burners. Would a typical burner be able to program both EPROMS and EEPROMS? And would it also be able to erase EEPROMS, or do I need to make sure it supports that as an additional feature?

The ZX81X2 ROM that Mark linked to is the one I'm interested in as well. I'm sure I'll treat myself to an eprom burner in the next few months, especially once COVID starts settling down and things return to a bit more normality (hopefully).

Ian
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1024MAK
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Re: Attic 81's - My collection and attempts to repair

Post by 1024MAK »

sheddyian wrote: Sat Jan 09, 2021 5:34 pm Thanks for all the replies and info about ROMS/EPROMS/EEPROMS.

I think it's a medium term project given the extra cost that I'd rather not spend at the moment, but I'll keep an eye on ebay for cheap EPROM burners. Would a typical burner be able to program both EPROMS and EEPROMS? And would it also be able to erase EEPROMS, or do I need to make sure it supports that as an additional feature?
If you mean new programmers, yes they should be able to ‘burn’ and erase EEPROMs. If you mean previously owned older programmers, it depends on how old it is and what devices the manufacturer included support for.

EEPROMs that can be programmed from a single 5V supply, can be programmed in-system on some 8 bit computers or via a user port or printer port, or by using Arduino or similar microcontroller devices.

Mark
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mrtinb
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Re: Attic 81's - My collection and attempts to repair

Post by mrtinb »

I have built this one - the MEEPROMMER. A shield for the Arduino.

I used the gerber files and ordered some in china. They are just PCBs so you have to add the components yourself. I can one the for a few euros + shipping.
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ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
sheddyian
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Re: Attic 81's - My collection and attempts to repair

Post by sheddyian »

mrtinb wrote: Sat Jan 09, 2021 11:16 pm I have built this one - the MEEPROMMER. A shield for the Arduino.

I used the gerber files and ordered some in china. They are just PCBs so you have to add the components yourself. I can one the for a few euros + shipping.
Thank you, I will have a look at that. I am aware of Arduinos but don't have one and have never used one, so there could be a learning curve for me here.

Also my electronics skills may be lower than I imagined.. see next post.

Ian
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Re: Attic 81's - My collection and attempts to repair

Post by sheddyian »

Yesterday I fitted an internal 16K upgrade to ZX81 #3. I also moved the late revision ULA to this machine, where it gives a better picture than it did when fitted to ZX81 #1. No shadowing, no flickering, lovely crisp bright display from the UHF on a colour TV.

To upgrade to 16K, I followed the Tynemouth instructions, accessed via Wayback machine : https://web.archive.org/web/20200929054 ... rsion.html This is the reversible version that doesn't require any track cutting - I felt this was safer for me :lol:

My soldering was a bit clumsy, but I checked it out with a meter : continuity is good and no shorts are apparent.

I powered it up, and got the K cursor. Success! (maybe)

I successfully ran the CLKFREQ.P program and showed the expanded ZX81 runs faster (separate post) and was happy with this.

I then tried to load some 16K programs. This is where it went downhill.

Using TapeUtils Java program running on a Linux laptop, which has worked well for me with 1K programs so far, I tried to load 3D Monster Maze .

The Zeddy craps out within 1 second of starting to play the audio into it's EAR. Back to a K cursor. I downloaded a different copy of 3D monster maze, this does the same thing.

I tried Mazogs, same result - it fails within 1 second of starting to show the loading noise on the TV.

I then randomly chose Dragon Maze which I hadn't heard of before, and this loaded OK and ran.

I've tried Mazogs and 3D monster maze again today, they still fail.

I note the program size may be relevant. Shown here, as reported by tapeutils :

3D Monster Maze 10553 bytes
Mazogs 12832 bytes
Dragon Maze 4751 bytes

So.. the smaller program loads but the larger ones fail very quickly.

I wondered about memory faults or a failure on my part installing the upgrade.

I found this test program https://sinclairzxworld.com/viewtopic.php?t=2664

Here I compare the results this program tells me with the example shown in the post above :

Code: Select all


RANGE			ME		EXAMPLE
=============		===		========
0K TO 8K IS RAM		NO		NO
8K TO 16K IS RAM	NO		YES
16K TO 24K IS RAM	YES		YES
24K TO 32K IS RAM	YES		YES
32K TO 40K IS RAM	NO		YES
40K TO 48K IS RAM	NO		YES
48K TO 56K IS RAM	MIRROR/16K	MIRROR/16K
56K TO 64K IS RAM	MIRROR/24K	MIRROR/24K

MEMORY  FOR BASIC	16K		16K

PEEKing RAMTOP shows 32768, which I beleive indicates the ZX81 thinks it has 16K.

I don't know the author's configuration, and I'm not very familiar with ZX81 memory layout.

So, advise please :

What do you think of the output from the program? Does anything look wrong?

Why might a 16K program fail to load within 1 second of starting the loading?

Is there a different/better memory test program that perhaps POKEs and PEEKs all/most available locations to see what is available and detects faults or incompetent wiring by 3rd parties (ie, me)

Thanks

Ian
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