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# 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)
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