# Sinclair ZX Spectrum 48k+ ## Child of the 80's Like many children of the 80's my first computer was a Sinclair ZX Spectrum. I spent many hours on it playing games, bought magazines, books and even tried my hand at programming. Programming for me at that time meant typing out long pages of machine code that often resulted in several wasted hours. Rarely did it work... ## The motivation It's been a strange week. Somehow the topic of Z80 computers came up and I started doing a little digging. I actually had no idea, or had forgotten, that the humble ZX Spectrum had a Zilog Z80 processor at its heart. Remembering that I still had one complete Sinclair Spectrum 48k+ and a case in it's original box (from my original Spectrum) in the loft, I felt motivated to do something with them. Sadly a day or two later came the news of Sir Clive Sinclair's passing. The man who had inspired a generation of computer enthusiasts with his accessible home computers was gone. The news both saddened me and strengthened my resolve to bring my Spectrum back to life, as a personal tribute to this great man. ## Bringing it back to life My first task was to get the computer and box out of the loft. To my surprise there was also an original Boots cassette player up there too. Unfortunately on inspection the complete Spectrum wasn't in great shape as it had been left in a damp loft for many years. The case that was inside the box however was just as fresh as the day I put it in there in the late 80's or early 90's. The reason the case was empty was that I had bought a better quality case for it with a PC style keyboard. I cleaned off the main board[1] as best I could and took note of the issue number so that I could order a replacement capacitor kit. After doing some reading up and watching youtube videos detailing the restoration process, I ordered a capacitor kit. This kit[2] included a full set of replacement capacitors, a heatsink for the ULA and a 100uf capacitor to perform a composite mod. While waiting for the kit to arrive I tried to assemble the various bits of Spectrum hardware I had laying around. I managed to find a power-play joystick interface and a Currah Speech interface along with its manual. Unfortunately I couldn't find the PSU or cassette cable... *WARNING* - If you have an old computer such as this, do not attempt to power it up without first changing the capacitors. It is likely they have dried out and are way out of specification. Attempting to power up the system could result in destroying other sensitive electronic components on the board or even a fire. ## Capacitor replacement Replacing the capacitors was a little fiddly but I knew what to expect after watching several youtube videos. I did the composite mod first, then I replaced the capacitors one by one, making sure I replaced each with the correct value and in the correct polarity. The whole process took me an hour or so to complete and I was fairly satisfied with the result[3]. ## Cleaning and reassembly I spent some time cleaning up the edge connector with a fibreglass pen and removing any remaining solder flux. The board was then given a light scrub with contact cleaner. On checking my original case, everything was in good order and just required a light clean inside and out before beginning reassembly[4]. The computer is now back in one piece[5] and awaiting a modern switching PSU to arrive so that I can test the system. ## PSU arrived (20/10/2021) It doesn't work... The power supply arrived about a week ago but I was too disappointed to do anything more with it. The past few days I have been investigating the issue with a multimeter and reading up online. It seems that a common fault with these old spectrums is the lower memory modules become bad, either with age or from other issues that affect the voltages going to the chips. The result is garbled colours on the TV or black & white bands and other vertical lines. ## Lower Memory The lower memory consists of 8 x 4116 chips[6] and requires 3 separate voltages (-5v, +5v and +12v). If any one of the voltages goes too far out of specification it can damage the chips. Having checked all the voltages everything seems to be within specification, so I can only assume they have just expired through age. From what I have read they are quite prone to failure and also becoming increasingly hard to come by. Thankfully there are options to replace the problematic 4116 chips: 1) Purchase an all in one Lower RAM replacement board[7] 2) Use 4164 upper memory modules Both options require removal of all 4116 lower memory chips. ### Lower RAM replacement board The easiest, and cheapest, repair is option 1. The board requires soldering only the necessary legs from the daughter board to function, rather than all 16 legs of every replaced chip. It does however not look pretty, IMHO, so if you are hoping to keep your spectrum looking original then you may want to consider another option. It does use modern chips and a single voltage however, so it should be more energy efficient, generate less heat and be more reliable. ### Use 4164 memory modules Using 4164 chips, which seem to be more robust and available, is an option I considered. Unfortunately it works out more expensive and is quite a bit more work. It would however retain the aesthetic of the original unit. If I had gone this route I would have socketed all the lower memory, so that future replacement would be fairly trivial. The 4164 uses only a +5v feed and so requires some modification to the chips, or the board, to remove the unnecessary voltages and supply +5v to pin 8. I wanted to avoid making many changes to the board and make the changes easily reversible. The 4164 requires no -5v to pin 1. Looking online people have solved this by simply cutting off the leg of the chip, this saves breaking any tracks on the board, but obviously you are damaging the chip and preventing later use for some other application. The +5v to pin 9 can remain in place, but we need to provide a +5v feed to the pins which provided +12v to the 4116 chips. The only neat way I could see of doing this was to cut the 12v supply track somewhere near the positive terminal of capacitor 44[8] of my model 4B board. Then a short bridge wire could be installed between the nearby +5v and previous +12v rail to provide the required power for the chips. *NOTE* - The above 4164 modification is speculative. This modification is untested by me and I have no source proving it would work. ### Removal of 4116s (23/10/2021) Knowing this was going to be tricky, I ordered a good quality solder sucker to make the job a little easier. Even with the premium solder sucker it took me the best part of 3 hours to carefully remove the lower memory[9][10] without damaging the chips. ## Ordered Parts (24/10/2021) Placed order with retroleum.co.uk for: 1) lower memory module 2) switching power regulator 3) mono cassette cable 4) 8x 16 pin IC sockets ## Parts arrived (30/10/2021) I was quite excited to receive the package in the post this morning, so I quickly got all the soldering gear out and set to work. I replaced the power regulator first, followed by the memory module, taking care not to get the legs too hot. Unfortunately, upon testing, there is still a problem. The thick black and white bands have now gone, but the coloured blocks that are alternating background and foreground colour remain. I don't know what the problem is, practically everything has been replaced. The only notable thing is that TR7 is rather hot and there is a quiet wheezing noise coming from the speaker... At this point I have put around 40GBP and 6 hours of my time into restoring it and I'm about all out of enthusiasm to invest any more time or money. ## Ordered Parts (09/11/2021) Placed order with retroleum.co.uk for: 1) 1x 28 pin DIL socket 2) 1x ROM replacement module After emailing Phil at retroleum.co.uk and explaining my continued issues he suggested that it would be best to try identifying the problem with a diagnostics ROM, rather than blindly changing components. For less than 10 pounds, including postage, it seemed like a sensible thing to do. The side benefit of this approach is that the ROM module has a switch and can be programmed with two ROM images. I chose the standard Sinclair 48k ROM and his diagnostics ROM ,so if there is a problem with my original ROM the new one can be left in place. ## Parts arrived (12/11/2021) I took my time desoldering the ROM module and then proceeded to solder in the DIL socket. The DIL socket will allow easy replacement of the ROM in future. Once the socket was installed I fitted the ROM card and connected the board up to a TV and PSU. To my surprise the Sinclair copyright logo appeared! It would seem that the issue was with the original Sinclair ROM. I switched it off and connected up the keyboard but unfortunately only some of the keys worked. At this point I knew the system was working and needed a replacement keyboard membrane. I figured having gone this far I should get one ordered. ## Ordered Keyboard Membrane (24/11/2021) After reading on the retroleum.co.uk website why Phil doesn't supply spectrum + membranes and reading on his blog that he had a good experience with one provided by RAWP. I proceeded to order one from them via sellmyretro.com[11]. Unfortunately not the cheapest option at almost 20 pounds, including shipping. ## Membrane arrived (03/12/2021) I fitted the membrane without issue and on testing all keys functioned as they should, result! I installed the 'ZX Tape Player' app to my android phone and, with the volume turned up to full, managed to load and play a game or two of 1943 & Jetpac. [1](gopher://gopher.icu/I/phlog/Computing/images/spectrum/before.jpg) [2](gopher://gopher.icu/I/phlog/Computing/images/spectrum/refurb-kit.jpg) [3](gopher://gopher.icu/I/phlog/Computing/images/spectrum/after.jpg) [4](gopher://gopher.icu/I/phlog/Computing/images/spectrum/base.jpg) [5](gopher://gopher.icu/I/phlog/Computing/images/spectrum/complete.jpg) [6](https://sinclair.wiki.zxnet.co.uk/wiki/DRAMS) [7](http://retroleum.co.uk/zx-spectrum-chips) [8](https://spectrumforeveryone.com/wp-content/uploads/2017/08/ZXSpectrumIssue3b-Layout.gif) [9](gopher://gopher.icu/I/phlog/Computing/images/spectrum/lower-ram-fr.jpg) [10](gopher://gopher.icu/I/phlog/Computing/images/spectrum/lower-ram-bk.jpg) [11](https://sellmyretro.com)