Correction: Dave Curran is doing a blog on the Spectrum clones - not a video :) When I measured the impedance of the speaker, the other point I forgot to mention - it's not just about impedance, its the power rating too (watts).
I don't think the internet is ready for my videos yet, so I'll stick with the words and pictures blogs. The 'How does the Spectrum work' may be a while. I've done the VIC20 and the ZX80, and I'll be doing the ZX81 next (using my ZX81 compatible Minstrel 3 boards) and then will come the Spectrum with reference to the Harlequin. In the meantime, I can highly recommend Chris Smith's ZX Spectrum ULA book if you really want a deep drive into the inner workings of the Spectrum ULA.
Long time ago I put a mechanical keyboard on my spectrum. For connectors I filed down the thickness of some PCB and filed the copper into strips for pins, then soldered on ribbon-cable, worked a treat.
Great video that, given how few logic chips are needed to reproduce the ULA I'm almost surprised these clones weren't more readily available back in the day, a simple design indeed. I could see this being possible to make in Hong Kong backstreet factories, minus the ROM chip for pennies even in 1982.
I just opened up my (unassembled) Harlequin kit from ByteDelight and almost all of the chips are "HC" chips. The exceptions are the RAM chips, the ROM chip, and a Texas Instruments TL712CP.
These are 74HCxx chips, i.e re-implementations of older bipolar TTL functions (74LSxx etc) in CMOS. The modern RAM and ROM are CMOS as well. The Z80 could be either n-MOS or CMOS (both works).
My Harlequin 128 will not start after soldering. It showws only mosaic. I checked every 74hc... chip using eprom programmer. It showed, the 74hc166 (as you point) is damaged. Replacing didn´t help. Z80 seems to be working. Pin 6 shows some square-like wave. Do you have an idea?
It can be tricky to diagnose builds of these boards over the net! I would check that every component is correct, ie. transistors the correct way around, the correct 74 series is fitted in the correct socket, and correct with regards to pin 1. You could check that 5v and ground are getting to every 74 series correctly too. Check the ROM you are using is correct too, and the associated jumpers (if those jumpers are wrong it will not boot correctly).
when i fitted a "clicky" 48k keyboard for a customer earlier in the year it was the type that fits under the rubber keys, though the one in the video can be fitted under rubber keys if you wanted. anyway the membrane slots were mangled and i wasn't getting good contact with them, the replacement keyboard had the same grey ribbon as the one in the video, after checking with the customer i soldered the ribbons direct to the board, and did away with the slots the guy i did it for said he would never go back to the original membrane, so fitting permanent was a good option.
I just got a harlequin 48k board that I purchased in a LO -PROFILE retro Keyboard. The keyboard does work. I inspected the contacts and the sockets and even reflowed the socket solder points on the harlequin RevG. When I connect the keyboard upto an original 48K rev4 board - it works. So something is wrong on the Harlequin board. Sometimes when I press the keys it double registers the key press. Again this is erratic. I don't have any schematics to where the keyboard would be linked to which IC? Do you think its an IC issue? Perhaps the wrong type or failed IC which works the keyboard? Appreciate any of your insight. Your vids are a great masterclass!
Yes, or to decode upper bits of the address to make the chip selects for memories. The ZX80 used only logic gates for its address decode. 138's outputs go low one at a time making it idea for the job, It also was common on some earlier 16 bit designs. I used them in an early 8086 based product to decode PROM and RAM space accesses.
About time someone created a multithreaded Sinclair basic and made one with many 8 bit processors in parallel plus floating point units and improved graphics. Develop a Spectrum for the new millenium, something powerful, user friendly, but with real possibilities in what it can achieve.
Last week I had a problem with a DivMMC that killed one of my speccys and had exactly the same behavior, first black/white screen and after that when checking with the scope signals it started "loading" xD In my case the DivMMC killed some of the address lines of the Z80.
Nice job. I got a Harlequin 128K, but aren't done soldering yet. I was also confused which rom(s) is/are correct to burn onto the Eprom. There are so many rom files, I am confused. Any hint?
With regards to the 128K - honestly not sure! I don't know whether you have a single ROM chip containing 48K and 128K basic or what. On these 48K boards, you can just stick the original Sinclair ROM straight onto a 27C512.
5V logic is generally good to over 6V on the supply. I would suspect a bad socket too. Those are not very good sockets. They only make contact with a single spring element that is formed by bending the metal. A bit of debris or the like can make for a bad contact. Also check PAL vs NTSC video.
For a short period of time it might be OK, but a quick glance over a few 74 series datasheets and that tells a different story! They normally have a max operating voltage of 5.25v, some maybe 5.5v. CMOS chips tend to be OK over 5v though - eg. some of the the MOS parts on the C64.
@@GadgetUK164 The parts only meet specs at the 5V +/- 0.25 AKA 5%. They don't get damaged up until about 7V. They also tend to fail when hot. My main point was that I doubted the voltage regulation was an issue.
I didn't notice any! I would be surprised if there was any lag as it's pretty much an exact copy of a Spectrum! My TV possibly introduces some lag, but I've never noticed it!
One thing I don't get is why should those chips be HC and not HCT or LS? Well, LS are power-hungry, so I can see why you don't want to use them. From my point of view there is no need for pure CMOS, i.e. HC chips. The real issues were the transistors mounted the wrong way and the use of a 74138 instead of a 74166. The board should work with both HC and HCT.
The parts list I was provided specifies HC parts! But I agree LS and HCT in many places on there would probably work! HC is faster than LS I believe, besides which the different logic levels. Since more than 50% of the board was HC already, it makes sense for the rest of it to be HC too. When you mix HC and LS you can get timing issues you might not have intended in certain parts of the system. My understanding is the original ULA was probably a CMOS part.
Correction: Dave Curran is doing a blog on the Spectrum clones - not a video :)
When I measured the impedance of the speaker, the other point I forgot to mention - it's not just about impedance, its the power rating too (watts).
I don't think the internet is ready for my videos yet, so I'll stick with the words and pictures blogs. The 'How does the Spectrum work' may be a while. I've done the VIC20 and the ZX80, and I'll be doing the ZX81 next (using my ZX81 compatible Minstrel 3 boards) and then will come the Spectrum with reference to the Harlequin. In the meantime, I can highly recommend Chris Smith's ZX Spectrum ULA book if you really want a deep drive into the inner workings of the Spectrum ULA.
Another quality repair as always Chris, love the work you do keep it up 👍
Long time ago I put a mechanical keyboard on my spectrum. For connectors I filed down the thickness of some PCB and filed the copper into strips for pins, then soldered on ribbon-cable, worked a treat.
Great video that, given how few logic chips are needed to reproduce the ULA I'm almost surprised these clones weren't more readily available back in the day, a simple design indeed. I could see this being possible to make in Hong Kong backstreet factories, minus the ROM chip for pennies even in 1982.
Great repair, those types of kits are super cool.
Thanks =D
Never knew about this, Wouldn't mind having a go at it!
Great video as always❤️👍
I just opened up my (unassembled) Harlequin kit from ByteDelight and almost all of the chips are "HC" chips. The exceptions are the RAM chips, the ROM chip, and a Texas Instruments TL712CP.
These are 74HCxx chips, i.e re-implementations of older bipolar TTL functions (74LSxx etc) in CMOS. The modern RAM and ROM are CMOS as well. The Z80 could be either n-MOS or CMOS (both works).
My Harlequin 128 will not start after soldering. It showws only mosaic.
I checked every 74hc... chip using eprom programmer.
It showed, the 74hc166 (as you point) is damaged.
Replacing didn´t help.
Z80 seems to be working. Pin 6 shows some square-like wave.
Do you have an idea?
It can be tricky to diagnose builds of these boards over the net! I would check that every component is correct, ie. transistors the correct way around, the correct 74 series is fitted in the correct socket, and correct with regards to pin 1. You could check that 5v and ground are getting to every 74 series correctly too. Check the ROM you are using is correct too, and the associated jumpers (if those jumpers are wrong it will not boot correctly).
when i fitted a "clicky" 48k keyboard for a customer earlier in the year it was the type that fits under the rubber keys, though the one in the video can be fitted under rubber keys if you wanted.
anyway the membrane slots were mangled and i wasn't getting good contact with them, the replacement keyboard had the same grey ribbon as the one in the video, after checking with the customer i soldered the ribbons direct to the board, and did away with the slots the guy i did it for said he would never go back to the original membrane, so fitting permanent was a good option.
I just got a harlequin 48k board that I purchased in a LO -PROFILE retro Keyboard. The keyboard does work. I inspected the contacts and the sockets and even reflowed the socket solder points on the harlequin RevG. When I connect the keyboard upto an original 48K rev4 board - it works. So something is wrong on the Harlequin board. Sometimes when I press the keys it double registers the key press. Again this is erratic. I don't have any schematics to where the keyboard would be linked to which IC? Do you think its an IC issue? Perhaps the wrong type or failed IC which works the keyboard? Appreciate any of your insight. Your vids are a great masterclass!
Nice one. 74xx138 is an address decoder. Very common on 8-bit computers. Used to map hardware to an address in memory.
Yes, or to decode upper bits of the address to make the chip selects for memories.
The ZX80 used only logic gates for its address decode. 138's outputs go low one at a time making it idea for the job, It also was common on some earlier 16 bit designs. I used them in an early 8086 based product to decode PROM and RAM space accesses.
About time someone created a multithreaded Sinclair basic and made one with many 8 bit processors in parallel plus floating point units and improved graphics.
Develop a Spectrum for the new millenium, something powerful, user friendly, but with real possibilities in what it can achieve.
Good morning my friend.
Decaf coffee and watching the vid.
=D
hello graet video again keep them coming .. do you have a pdf for the amstrad 464 mainboard please
I don't have a pdf - CPC schematics can be found here:- www.cpcwiki.eu/index.php/Schematics
Last week I had a problem with a DivMMC that killed one of my speccys and had exactly the same behavior, first black/white screen and after that when checking with the scope signals it started "loading" xD
In my case the DivMMC killed some of the address lines of the Z80.
Could you use stripboard for the keyboard connectors?
Better use dupont connectors and call it a day (IMHO). 😁
Nice job. I got a Harlequin 128K, but aren't done soldering yet. I was also confused which rom(s) is/are correct to burn onto the Eprom. There are so many rom files, I am confused. Any hint?
With regards to the 128K - honestly not sure! I don't know whether you have a single ROM chip containing 48K and 128K basic or what. On these 48K boards, you can just stick the original Sinclair ROM straight onto a 27C512.
@@GadgetUK164 Okay, I will take another look!!
ZX-Spectrum - это моё детство! / ZX-Spectrum is my childhood!
What is the 'nagic' Flux you used in the Video? -Mark.
Chip Quik flux!
I saw those and thought, just give me an FPGA. 🤣
i would check all the transistors too, its dead easy even for a pro to fit them the wrong way round.
It looks like the connectors for (what I’m guessing are) the keyboard flat-flex look a little battle-worn!
5V logic is generally good to over 6V on the supply.
I would suspect a bad socket too. Those are not very good sockets. They only make contact with a single spring element that is formed by bending the metal. A bit of debris or the like can make for a bad contact.
Also check PAL vs NTSC video.
For a short period of time it might be OK, but a quick glance over a few 74 series datasheets and that tells a different story! They normally have a max operating voltage of 5.25v, some maybe 5.5v. CMOS chips tend to be OK over 5v though - eg. some of the the MOS parts on the C64.
@@GadgetUK164 The parts only meet specs at the 5V +/- 0.25 AKA 5%. They don't get damaged up until about 7V. They also tend to fail when hot. My main point was that I doubted the voltage regulation was an issue.
Was there lag on the joystick when you played manic minor? It sounded like it.
I didn't notice any! I would be surprised if there was any lag as it's pretty much an exact copy of a Spectrum! My TV possibly introduces some lag, but I've never noticed it!
Was that lens flare directed by Michael Bay?
LOL! =D
One thing I don't get is why should those chips be HC and not HCT or LS? Well, LS are power-hungry, so I can see why you don't want to use them. From my point of view there is no need for pure CMOS, i.e. HC chips. The real issues were the transistors mounted the wrong way and the use of a 74138 instead of a 74166. The board should work with both HC and HCT.
The parts list I was provided specifies HC parts! But I agree LS and HCT in many places on there would probably work! HC is faster than LS I believe, besides which the different logic levels. Since more than 50% of the board was HC already, it makes sense for the rest of it to be HC too. When you mix HC and LS you can get timing issues you might not have intended in certain parts of the system. My understanding is the original ULA was probably a CMOS part.
Дядя, где набор брал?
I think byte delight may sell them, or ZX Renew. www.bytedelight.com/?page_id=9 zxrenew.co.uk/
You need one of my Spectrum Gamepads. So much better to play with. :)
Sweet👍
nice vieo mate
Thank you
What the hell is that keyboard. Clickbait.
LOL!!!!