🇬🇧 dk'tronics Keyboard for ZX Spectrum: Part 3 (Power On - OK!) [TCE #0606]
29Made some progress. First ... before I forget again ... I designed the missing MicroDrive port bridge PCB that was originally included to extend the Sinclair Interface 1 edge connector. Of course, I could've also just made a longer ribbon cable ...
Anyway, I gutted the RF modulator can and just stuck a 100µF electrolytic in there, replacing the 470µF that was originally used for the composite mod. I thought 100µF was sufficient, but the picture looks a little noisier to me. Doesn't really matter as the vLA82 replacement ULA that I'm using has the option for RGB output, which I might as well use.
I did find a short on the underside of the board - two capacitor legs were touching. Didn't solve the issue though.
Without the vLA82 installed the Z80 still heated up very fast. I couldn't find any issue with the voltages - they all measured okay, and I couldn't find any shorts between them. So maybe the Z80 was just fscked.
It's not socketed so never an easy thing to just replace to see if it fixes it. But I've been using the Japanese-made ENGINEER SS-03 solder sucker quite a lot the past few months and it worked really well to remove the Z80 in this case - came off very cleanly.
I installed a socket and stuck a new (2021) Z80 in, still without the ULA. The current draw was immediately a lot lower and the Z80 remained quite cool. Sticking the vLA82 in and the Speccy booted!
Unfortunately it seems the keyboard key switches are a little bit dodgy so might need cleaning, if that's possible with these types ...
00:00 ... Intro
03:10 ... Dodgy dodgy
04:45 ... RF modulator can gutted
05:15 ... Checking underside of board
07:13 ... Z80 replaced
08:10 ... Power on ...
10:18 ... New keyboard connectors
12:45 ... Interface 1 & Speccy installed
14:09 ... Keyboard test
19:00 ... Channel thanks & outro
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From Part 2:
Let's have a quick look at the Issue 4S board ZX Spectrum+ board that came with the keyboard. The ULA was missing as was one of the 4116 16kbit DRAM chips that make up the lower 16KB of RAM. I noticed that the composite video mod. had been done already. Looks like the board might've been used for spares so might not be in a good state.
I used one of vRetroDesign Charlie's vLA82s to replace the missing ULA and substituted a 4164 temporarily in place of a 4116.
https://www.vretrodesign.com/
Looks like some troubleshooting is required ...
Dave of Tynemouth Software has an interesting blog post about repairing an Issue 4S board:
http://blog.tynemouthsoftware.co.uk/2018/06/zx-spectrum-mystery-repair.html
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From Part 1:
Let's have a look at this keyboard & case for the Sinclair ZX Spectrum from dk'tronics. As with the Fuller FDS keyboard & case, the Speccy must be denuded for it to fit. This case is designed to also accomodate the Spectrum's Interface 1 (also denuded) which adds MicroDrive, RS232 serial and network support to the Speccy, similar to the Fuller FDS.
There's not much to it. The keyboard is okay, nothing spectacular. It has a lot of space inside which would allow your Speccy to breath a bit more, although you can also fit your power supply inside as well. It apparently came with a double-ended PCB that you could attach to the MicroDrive port on the Interface 1 to allow your MicroDrive cable to connect from outside.
The Speccy that it came with is an Issue 4S and is missing its ULA (not a major issue). It also has a reset button attached (I assume), although it's floating free rather than affixed to the case.
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