Spectrum Computing

Some spectrum joysticks could assign anything that had a key... The logical conclusion would be to avoid joysticks and have your control system specify keys. Then you can assign up to 40. Way back I remember making a "cockpit" out of an old fridge box, lots of sticky tape, and rewiring a s...

I learned basic z80 code on the Spectrum and it got me my first job as a z80 programmer in a video game factory R&D department. It was an awesome job to have as a kid... Anyway, the Spectrum isn't ideal to learn machine code on. Get an emulator and learn on that if you can, then transfer that kn...

I'd say it's extremely unlikely to be the capacitors. Looks like a stuck address bit... Address Bit 0/7 - Pin 5 to all the DRAM chips... Probably stuck low. On the ULA/4116 side of the resistors. There's only 1 or 2 capacitors on most speccys that can cause trouble with age. Most of the others won't...

4116 RAM chips are inexpensive and easy to get from China presently. And if uncertain, a 4116 DRAM tester is also relatively cheap. 8118 should also be OK, but will require changing rails as you noted. Though if the pins really are NC on 1 and 9, it probably won't matter much whether the board is mo...

Or, since the important signals are available at the expansion port, you could just make an external PCB with the missing components, and make the entire thing external with 1 or 2 drives, and a Spectrum bus interface.

Another option is MFM modulation, like in floppies and early hard drives. It would double the speed. Or RLL... But the challenge is doing it in software. At some point external hardware is required to support the solution and recover the clock. Even the Spectrum software based solution can be impro...

They even made a video camera that used audio cassettes, so cassette bandwidth is actually pretty impressive if pushed to the limits.

https://www.popularmechanics.com/techno ... cassettes/

Did it involve switching to 48k compatible mode? Or did it use the 128K banks?

Did you check the alignment of the ROM selection jumpers? Not all roms are the same, and this varies even between batches of the same model.

And yeah, it's not going to work with it missing either, for obvious reasons.

Time to get an oscilloscope

More than the M1 gets damaged by misaligned interfaces... And frequently it killed the entire spectrum. I suppose the M1 fault is simple a fault that doesn't result in the machine's immediate failure as it wasn't really used for anything. So when this was the only resultant, it's likely no one reali...

Most faults with spectrums are the lower 16K ram bank.

Most ram bank faults looks similar.

Most repairs begin the same way. Check the voltages to the lower RAM and see if it's -5, 5 and 12v.

After than a diagnostic cartridge is the next step.

Power is only used when the joystick has active circuitry, or is analog or is a mouse. It is possible to build a Kempston interface that populates both the Joystick register and the Mouse register at the same time, so both items will work in it like an autodetect, though I'm not sure that all softwa...

It's not trivial, but you could use the microdrive sector map as a hash of sorts and see which drive matched it, but it would have to search the maps. Or you could set an unusual name on the drive, and read the motors and once you had a sector header, see if it matched the cartridge name and then sw...

So some chips came in and I built the video card out of 6 chips - 2 would have been GALs and one the memory chip (64K x 1) but the other three could have been latching or tristating buffers that act as arbiters and latch the video signal for the output stage. I built the proof of concept PCB and tur...

Colour me impressed, any by colour I mean with attribute clash...

But still impressed nonetheless

Nice work!

Not broken, because the CPU can read and write it just fine.... Just out of tolerance.

Write a basic program to write bits to the screen to work out which one it is, and replace it.

It's an issue that only seems to affect Greys.

David

It's not like it's difficult to replace a ULA. https://www.tindie.com/products/CharlieIngley/vla82-spectrum-48k-ula-replacement/ Though that might not be the issue... There's a range of troubleshooting steps you could take first - though the video breaking up may be the ULA. I'd probably check the s...

I've usually only seen the top left one, and I think maybe the bottom left way back in the day. There was also a plain unmarked box that said "Receipted Postage" and had no other identifying marks, except the recipients address for people who got their early Spectrums by Mail Order. It jus...

Sounds like some broken components if you're reading +9v on Pin1 of the 4116 sockets.

If you dont need the negative rail, then 12v is only needed for the video output circuit.

They affect which pin the select signal goes to on the ROM and address differences in the ROM. One way the send ROMCS ( Decoded ROM chip select ) to Pin 20 as normal, and send MREQ to Pin 27 The other way, they send MREQ to Pin 20 and ROMCS to Pin 27. I can't remember if it was differences in the RO...

Voltages to the RAM chips?

You should never change the rams before you check the voltages, or you may break the replacements.

Make sure -5v and 12v are present and reasonably accurate on the chips ( within 10% )

First check your voltages - you need -5 12 and 5v for the lower 16K to run. Measure these on the chip. https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.evolutional.co.uk%2Fmedia%2F4116%2F4116-pinout.PNG&f=1&nofb=1&ipt=7a778a22f742284476792ebb5e89a4e5ae4614d984303b9a7c8f4b8...

Thanks again for the input and clarifications. Being self taught in electronics, these are the sorts of discussions I learn loads from. I need to go away and study. :geek: Nothing wrong with that - This is *exactly* how I started too. In fact, pulling out a "Shadow of the Unicorn" dongle ...

You would do it the same as the Interface 1 does. You always assert ROMCS when you want to run your ROM. If you replace the BASIC ROM you can leave it asserted. Having a copy of the BASIC ROM in your own rom and paging works OK too. Select your chip via an open collector and a pull-up resistor. Conn...

Interestingly, also in 1985, two different kinds of video ram were appearing, static video rams and dynamic video rams. Dynamic video rams were dual-port, but required a complex video controller as the line address had to be written into the video ram from the computer side of the bus, so some conte...