ZX Spectrum Projects – Diagnostic & Repair

November 1, 2019

Now I’m back on my retro computers I’ve put together this quick guide for those looking to diagnose and repair ZX Spectrum computers.

Schematics and Service Manuals:

Having a set of schematics or even better a full service manual is the good thing to have before starting any repair. Fortunately for us, full schematics and service manuals for the all ZX Spectrum models are available on the web. I have my Speccy schematics printed out on the biggest paper size I’ve got access to, namely A3. The service manuals are a great place to start when looking to diagnose a fault.

Schematics and Service manuals can be found at:

World of Spectrum

Spectrum for Everyone

IC Data sheets

wikipedia
7400 series
4000 series
Zilog Z80

Diagnostic Software Tools:

Happily the ZX Spectrum has quite a few diagnostic software tools to help the would be fixer in his fault diagnostics. Most of these are based on external ROM device which avoids the need to have a fully working Speccy or the problem of loading diagnostic software from tape.

Here’s a few ROM based diagnostic tools

Brendan Alford on github has “ZX Diagnostic”

Paul Farrow of fruitcake has the following ROM tools: 128K RAM Tester & ROM Tester
he also has the official Sinclair Test ROM as well
Phil Ruston of Retroleum has the following “ZX Spectrum Diagnostic ROM”

Tools needed:

Hand tools
Side cutters
Pliers
Screw Drivers: Philips and flat blade
IC extraction tool

Soldering Iron
De-soldering tool

Multimeter

Advanced
Oscilloscope
Power Supply (Adjustable/current limited)

Diagnostic software tools (see above)

TV Monitor/Screen (or car reversing monitor for composite video)

Repair mat
Anti static wrist or foot strap
IPA Wipes (no not the beer) – Isopropyl alcohol to clean edge connectors and contacts

Good web sites:

If the your own best efforts have not yet found the problem then there several good web sites that share their repair achievements where you can search. I like the following sites:

Dave Currah of Tynemouth Software

nightfallcrew

If you’re still no wiser, then try asking on one of the various Retro Computing Forums or general electronic forums in their repair section if they have one.

Remember to share as much information about the Speccy model, what it is not doing and what you have tried so far. Avoid simple statements like “Speccy not working please help”. It goes without saying that following the forums etiquette for posting will usually get you a more productive and polite response.

World of Spectrum forums
https://www.worldofspectrum.org/forums/

These are more general forums:
atariage forums

EEV Blog fourms


ZX Spectrum Projects – HD Video output

October 28, 2019

I’ve neglected my retro computer collection for a while now, so recently I’ve been dusting off my collection, starting with the ZX Spectrum to start some new projects with them. Whilst I have a few that need repairing I quickly got distracted into wanting to make a cool project for them.

Getting the Speccy to work with modern TV’s is becoming more of a problem. I’ve made composite video modifications to my Speccys in the past, I even made a small PCB that fits into space where the existing video modulator sits. But I want to see if HD / High Definition video was possible. By HD video I mean either VGA, DVI, DisplayPort or HDMI.

A quick web search found me Victor Trucco’s TK Pie. This is an interesting way of using a Raspberry Pi Zero to provide a High Definition (HDMI) video interface to the Speccy. It uses a mix of external hardware (CPLD) and the processing power of a Raspberry Pi Zero to capture writes to the Speccy’s video RAM and convert the pixel data into HD video via the Pi’s HDMI. There’s a similar project for the BBC Micro called RGDtoHDMI.

Here’s a link Victor’s web site and TK-Pie source code files

There are couple of useful reviews of TK Pie by GozdniJezek, Building TK-Pie by Victor Trucco

and martin@8bity, HDMI output for Sinclair ZX Spectrum – TK-Pie

Some more searching found me the next two devices. They don’t seem to be DIY projects but I thought they looked interesting.
Ben Versteeg at ByteDelight has ZX-HD: The story of the ZX-HD

and also Goran Radan with his ZX-VGA-JOY


No eDay this year

September 27, 2019

It’s around its time of year I would be getting ready some projects for our local eDay and like our local Maker Faire, eDay too has been cancelled 😦

But fear not after speaking to the organisers I’ve found out it’s been cancelled due to building work that is happening at the venue. So here’s hoping eDay returns back to its usual time next year.


Need a controller that is more powerful than an Ardunio but smaller than a Raspberry Pi?

August 9, 2019

Like most makers my staple for controller boards has been a mix of Arduino Nano, Uno and Mega for small embedded type applications with modest computing capacity and memory and the Raspberry Pi Zero, 3’s and 4’s for bigger computer type applications with much more computing capacity and memory. But what if you want something in between? What other boards are out there?

There are two recent developments that have caught my eye.

First is the new Teensy 4.0 Development Board from PJRC. I’ve used Teensy boards and supported previous PJRC Kickstarter campaigns in the past and found them to be really good boards with good software and great support. The latest board from them shows a significant increase in computing capacity, program memory and data memory.

Here’s its specs.

Processor: NXP iMXRT1062, ARM Cortex-M7
Clock: 600 MHz
Memory: 1024K RAM, 2048K Flash
Storage: none
Sensing: 14 x ADC
Actuation: 31 x PWM
Connectivity: 3 x SPI, 3 x I2C, 7 x Serial, 2 x USB, 3 x CAN Bus, 2 x I2S, 1 x S/PDIF, 1 x SDIO
I/O: 40 x GPIO
Operating System: none

The other board that I’ve been watching is the GiantBoard from Groboards. They have just finished (8/09/2019) a successful crowd funding campaign on crowdsupply.

Their board is based on Adafruits Feather form factor and has the following spec:

Giant Board Specs:

Processor: Microchip SAMA5D2 ARM Cortex-A5 Processor
Clock: 500 MHz
Memory: 128 MB DDR2 RAM
Storage: microSD card
Sensing: 6 x 12-bit ADC
Actuation: 4 x 16-bit PWM
Connectivity: 1 x I2C, 1 x SPI, 1 x UART. 1 x USB
I/O: 20 x GPIO
Operating System: Linux kernel 4.14

Neither of the boards have native WIFI, BT or Ethernet. Nor do they have any native video capability.


RC2014 enhanced prototype board now on Tindie

July 19, 2019

I’m please to announce that the enhanced prototype board/PCB for the RC2014 Bus I blogged about back in May is now on Tindie.

Also it’s schematic is here.


New Raspberry Pi 4

June 24, 2019

A bit out of the blue, comes a new Raspberry Pi. The 4th major revision of the popular SBC.

It’s spec looks very good. Faster processor, more RAM (choice of 1GB, 2GB or 4GB but at a price of more $$$), dual HDMI video, USB-C, Gigabit Ethernet, WIFI, Bluetooth 5.

Some things have changed on the new Pi. The connector positions have changed, so you’ll need a new enclosure and power is now provided by USB-C connector so you’ll need a suitable USB adapter or a new USB-C PSU. The dual HDMI are micro HDMI connectors instead of standard HDMI.

From earlier interviews with the Raspberry Pi foundation it wasn’t expected to be available until 2020 but it looks like Broadcom was able to get their latest SoC ready a good 6 to 9-months early.


No more Maker Faires ?

June 10, 2019

Very sad to read that TechCrunch reports financial troubles have forced Maker Media, the company that runs the Maker Faires and also the company behind Make magazine, is laying off its entire staff and stopping all operations.

This follows on from the sad news last year that Maker Faire UK had stopped.