stardot.org.uk

Would this other Dave happen to live in Scotland? And have his own web site detailing mainly a computer that was a competitor to the Sinclair range of computers?

Mark

If the SMPSU (switch mode power supply unit) internally has earth (ground) connected to any of the DC output connections, it's not a floating output. Some SMPSU have earthed outputs, but most do not (and their outputs are floating). The documentation should say which type it is. Or you can test it. ...

Is it worth having a ground/earth terminal post on a bench PSU? Yes. However, how it is used is another matter... When it comes to ground/earth, there are two types of power supply arrangement. Grounded / earthed and floating . With a grounded / earthed arrangement, one of the DC output conductors i...

I'm using MOS 3.20 for two reasons, first, it's the "standard' Master 128 MOS, secondly, I have never got around to upgrading the MOS in any of my Master 128's (I have two in working condition, but only one has a backup battery fitted, I also have a Master 512, but the keyboard needs a lot to TLC). ...

We'll, we now know that at least everything after the Videoproc (Video ULA) is working... Are you running with a 32k byte configuration (or trying to)? Ignoring other potential problems and concentrating on the video display system fault... It appears that the most likely problem is that the wrong a...

Forget the tin foil. Just put up a load of shelving and line up a row of at least ten working ZX Spectrum computers per outside wall, each running Manic Miner...

The resulting RF interference will confuse the hell out of whatever equipment "they" are using

Mark

An ideal capacitor should never get hot. Real capacitors in low power signal paths don't get even slightly warm, let alone hot. By low power, I mean low current. Electrolytic capacitors that experience high ripple currents (smoothing in power supply sections), some output stage coupling capacitors i...

Sooo, SPI as your next project?...

Mark

This brings up an interesting question. Apart from buying direct from the manufacturer, how would you know which sellers are selling a genuine programmer?

And along the same lines, if you already have a programmer, is there an easy way to tell if it is a genuine one?

Mark

Spares... (mine has a damaged case )...

Regarding the Starfighter joystick- PM sent...

Mark

Hi Tricky For the BBC A and B machines, the following applies for the OS ROM socket. /CE ( /CS ) CPU address lines A14 and A15 are decoded by IC21 to map the ROM to the C000 - FFFF range. This is the primary address decoding. This signal tells the ROM chip to get the data from it's memory at the add...

Good, the only mouse to have is one that works

Mark

The Beeb's OS ROM socket uses both /CE (/CS) and /OE, with the different signals coming from separate sources. So no, I don't think it would work without problems.

Mark

Stuart I think I have an AMX mouse somewhere, but it's likely in storage :( However, the principles are not too hard to understand. There are two signals for left / right, and two signals for up/down. I don't know what AMX called these signals, so I will call them X1, X2, Y1 and Y2. So when you move...

You took your time spotting that one
I been watching it for days...

Mark

I don't think using the analogue inputs would make any difference. I think this fault may be a problem with the electron beam scanning system. It looks like the horizontal scan may be partly working, but it appears to me that vertical scan is not working. Most CRT displays, when the brightness and c...

The other inputs are analogue red, green, blue and sync inputs (all terminated at 75 ohm). When using with a Beeb, you can ignore them. When using the DIN socket, the switch needs to be in the TTL position. I'm on a phone at the moment, so can't see the photo very well. Is it showing a bright horizo...

Elminster wrote: ↑

Thu Aug 16, 2018 9:31 pm

So /RSTA (pin 34 on 6522) goes low on power up only, and RST on pin 3 on 555 IC16 always flips on warm or cold rest. So that should be fairly easy to monitor while I poke about in other place.

Yeah.

Mark

The NE555 reset circuitry can certainly cause "lock-ups" / "freezing". At a past ABUG, I had a machine which did this when the Beeb had been on for a while. It turned out to be a contaminated PCB in the area where the NE555 and it's timing resistor and capacitor are located. After a good clean, it n...

The normal reset system uses a NE555 timer. This times whenever the system is powered up, or when the break ("reset") button is pressed.This reset signal resets the 6502 and also the user port 6522 and various other chips. This reset is available as inverted and non-inverted (/RST and RST). It's eas...

If you have a known good working Beeb, try any suspect 6522 VIAs in this...

Mark

A couple of points:- Despite being "standard" machines, each machine is slightly different, this is partly due to parts from different manufacturers, and partly due to manufacturing tolerances on those parts. With a high speed computer bus (which is what the TUBE is), adding a cable, especially a ri...

Wow, some deep diving into the inner workings of the Z80 CPU going on here

Mark

Rrad only 8271!

Is this for radioactive software?

Yes, older floppy drive system circuitry will use 150 ohm resistors. Keep in mind that up to four drives/devices are permitted on a floppy drive bus of this type (but Acorn systems only actually support two actual drives).

Mark

If the 6845 is working (needed to refresh the DRAM), a video fault like you describe should not affect the CPU side of the machine. Most likely two separate faults. Using the serial port to control the machine is rather fun :D When I first did this, it took me a couple of attempts to persuade it to ...

I think I have caught a cross-virus, a cross between a Big Clive bug and a Dave Hitchins bug :shock: Last week, I found myself in B&M buying a LED worklight, as featured on the Big Clive YouTube channel, plus various solar lights. Then today, I found myself in Aldi buying a Juice power bank... Befor...

Lardo Boffin wrote: ↑

Tue Aug 14, 2018 7:03 pm

I see that this has been downloaded a few times now. Anyone made any progress?

Admissions to the local mental help clinics have apparently gone up...

The Acorn Z80 runs at 6MHz.
The Torch Z80 runs at 4MHz.

I think there may have been confusion over which second processor was being talked about...

Mark

I wonder if a previous owner got a bit too aggressive with an upgrade/expansion, or when working on the board.
Resistors don't normally cause problems in Beebs, let alone break like you have described...

Mark