ZX80 Repair.
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- Posts: 45
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ZX80 Repair.
Hi all,
Looking for some advice. I bought a ZX80 about 5 years ago of Ebay. Only things i could see that we're obviously wrong was IC6 (74LS157) was cracked and I replaced this quite early on. Since then the computer has been sitting in my 'to-do' pile. Today I pulled it out and replaced the resonator, which was taped to the back of the PCB when I received it way back when.
Only thing else I have noticed is that there is piece of wire connected to pin 13 of the ROM. Should this be connected somewhere, to another pin on the ROM? The ROM is a Hitachi HN462532.
Cheers in advance
Andy
Looking for some advice. I bought a ZX80 about 5 years ago of Ebay. Only things i could see that we're obviously wrong was IC6 (74LS157) was cracked and I replaced this quite early on. Since then the computer has been sitting in my 'to-do' pile. Today I pulled it out and replaced the resonator, which was taped to the back of the PCB when I received it way back when.
Only thing else I have noticed is that there is piece of wire connected to pin 13 of the ROM. Should this be connected somewhere, to another pin on the ROM? The ROM is a Hitachi HN462532.
Cheers in advance
Andy
Re: ZX80 Repair.
A quick search of the forum will bring up a topic or two on the ZX80 ROM.
For example...
https://www.sinclairzxworld.com/viewtopic.php?t=3281
A couple of pictures showing the required mods for 2732 and 2532 EPROMS.
I can vouch for the 2732 version as I have tried it and it works, as for the 2532 I have no actual experience and can only presume the mod as shown is correct.
For example...
https://www.sinclairzxworld.com/viewtopic.php?t=3281
A couple of pictures showing the required mods for 2732 and 2532 EPROMS.
I can vouch for the 2732 version as I have tried it and it works, as for the 2532 I have no actual experience and can only presume the mod as shown is correct.
- Attachments
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- s-l1600.jpg (15.33 KiB) Viewed 968 times
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- eprom2732.jpg (35.86 KiB) Viewed 968 times
Last edited by Moggy on Sat Dec 30, 2023 2:50 pm, edited 1 time in total.
- 1024MAK
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Re: ZX80 Repair.
A photo would help...
Pin 13 is a data bus line. It's unusual for any wiring to be connected to any of the data bus lines.
Mark
Pin 13 is a data bus line. It's unusual for any wiring to be connected to any of the data bus lines.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
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- Posts: 45
- Joined: Sun Nov 03, 2019 9:56 am
Re: ZX80 Repair.
Hi thanks for the replys.
I have taken a couple of pictures already. But I'm assuming I have to use a photo hosting site to upload. Can anyone suggest a free one as I'm loathed to pay a fee for something I will only use on the odd occasion.
Cheers
Andy
I have taken a couple of pictures already. But I'm assuming I have to use a photo hosting site to upload. Can anyone suggest a free one as I'm loathed to pay a fee for something I will only use on the odd occasion.
Cheers
Andy
Re: ZX80 Repair.
There is a function for attachments. You'll see it at the bottom of the post. I'd recommend reducing the resolution to a reasonable level, as some cameras these take take gajillions of pixels. I normally reduce mine to about 1,200 pixels on the longest axis, or less if it still looks reasonable.
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: ZX80 Repair.
I believe the forum software shrinks photos to fit Perhaps Mark could clarify?
Just use the ATTACHMENTS tag, the ADD FILES tag, it's self explanatory from there.
Just use the ATTACHMENTS tag, the ADD FILES tag, it's self explanatory from there.
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- Posts: 45
- Joined: Sun Nov 03, 2019 9:56 am
Re: ZX80 Repair.
Hi guys.
Cheers for the help. Please see the picture.
I have no background on this machine, other than the solder looks professional rather than kit built. TBH the wire could have been jammed in there for 'reasons'??
There appear to be no other roach or bodge wires anywhere on the PCB or on the ROM. Certainly there appear to be no lifted pins etc.
Only other thing for me to do is change the 7805 as a matter of course. Again, the liklihood is this machine is unlikely to have been powered up in 35+ years. I'm not a big believer in changing components for the sake of it, but.
Andy
Cheers for the help. Please see the picture.
I have no background on this machine, other than the solder looks professional rather than kit built. TBH the wire could have been jammed in there for 'reasons'??
There appear to be no other roach or bodge wires anywhere on the PCB or on the ROM. Certainly there appear to be no lifted pins etc.
Only other thing for me to do is change the 7805 as a matter of course. Again, the liklihood is this machine is unlikely to have been powered up in 35+ years. I'm not a big believer in changing components for the sake of it, but.
Andy
Re: ZX80 Repair.
Looks wrong at a guess.
I would think the mod shown in the top picture I posted is probably correct as I seem to remember that this EPROM needs to have its programm voltage pin held at 5 volts when in use and the mod as shown would certainly achieve that.
I would think the mod shown in the top picture I posted is probably correct as I seem to remember that this EPROM needs to have its programm voltage pin held at 5 volts when in use and the mod as shown would certainly achieve that.
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Re: ZX80 Repair.
Yes, photo/picture/image files will be automatically compressed to save space.
There is also an absolute restriction on file size for any attachment. Also, the number of attachments and the allowed file types.
That looks, from your photo, like an off-cut of a piece of wire that has got lodged there. I don't know of any reason for this wire being there. If that was mine, or someone had asked me to service or repair it, I would carefully remove the EPROM to check the socket.avrovulcan wrote: ↑Mon Jan 01, 2024 3:24 pm TBH the wire could have been jammed in there for 'reasons'??
If you don't have experience of removing chips from sockets, please ask me to point you to some advice.
7805 voltage regulators are generally speaking, reliable devices. The primary reason that they get replaced now, is that they are not very efficient and they produce a lot of heat. Hence DC/DC converters/switching regulators (which run cool) are preferred if people are not bothered about keeping their machine 'original'.avrovulcan wrote: ↑Mon Jan 01, 2024 3:24 pm Only other thing for me to do is change the 7805 as a matter of course. Again, the liklihood is this machine is unlikely to have been powered up in 35+ years. I'm not a big believer in changing components for the sake of it, but.
If you suspect the 7805, supply the board with a 7V regulated supply and measure the output (+5V) with a multimeter.
If the output is within spec (4.75V to 5.25V) then it's likely to be fine.
If you do decide to replace it with another 7805, do buy a legitimate part, not a cheap substandard part from eBay or other trading site.
Agreed. The VPP pin needs to be connected to the +5V supply. Being connected to address line A12 is not recommended.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: ZX80 Repair.
Is there any way of telling these substandard parts from the legit ones, perchance? ... asks the person who certainly did not, in any way, shape or form, just buy some of these https://www.ebay.co.uk/itm/155949855428 from ebay.
Michelle.
All that I've learned - https://msknight.com/bbc/index.html#zx81