Recent content by Hugo Holden

"Ok I got the High Voltage Probe and measured the only transistor I could find in the power PCB, the K793 high voltage N-MOSFET with the following results" Gulp ! The power pcb contains the line voltage power supply. This system, on the primary side of the power transformer has no common...

It must have, as it can program ROMs with either 21 or 25V voltages. It sometimes requests for its external power adapter to be connected, but that is just a 9V@200mA wallwart, most of the time it just runs from the USB power, so it must contain voltage converters to step up to 21 & 25V.

@nullvalue, can you check the attached diagram and see if you agree with the placing of the holes. Since the panel on the Hammond enclosure is a little smaller in size, some scaling had to be done to keep the proportions similar so it looks like the original, except we are putting the button &...

I did some measurements and calculations, using the internal dimensions of the Hammond box, Some of the measurements don't exactly match the calcs because the folds in the metal are not perfect, and it slightly affects the inner dimensions, it is close enough to within half a mm or so. The...

It could , but I think we will find out when it is running if the volume required adjusting down, it may not, but at least there is space to add a resistor if required. From the photo, it looks like dimension A is greater than B for the joystick and knob array . Can you measure the originals...

I have attached the info required to make these boards. Since the audio output with the 8 Ohm speaker has about x3 the power of the 45 Ohm speaker system, it possibly could be a tad loud. So I added a link on the pcb where a resistor could be placed at the input, in series with the audio input...

I built a home made proto pcb . (In lieu of plated through holes on a proper pcb where wires pass into a pcb on these home made ones I use 1.5mm brass eyelets) I will test it out today. I want to run it up with an actual OP amp driving the the audio system, rather than a signal generator, just...

Yes, I agree, it is the next project to be targeted for replication. I suspect it would be a rare item to find either built or un-built. But if somebody has one and could provide the details, I think we (the Cromemco replica team) could do a good job on it.

That Monkey.mov reminds me of a Bruno Mars music clip.

I'll post just the track image and artwork. Probably this could be converted into a Gerber in little time ( by Gary maybe) in Kicad. I'll make a couple of boards by hand as well. I cannot see any issues, never hurts to double check everything.

How do you know the opto-couplers are dying ? there is no scientific evidence presented. Just because they are getting hot doesn't mean that they are dying or dead. If anything, one with an open circuit LED would be as cold as a cucumber as it would be if the LED were shorted out. If the...

@nullvalue wanted a pcb for this project. After looking at this for a while, I tend to agree, it is the way to go. It is all about keeping everything as orderly and tidy as possible. The original design was a little messy and it had the pull up resistors for the switches wired in a messy...

Multiple appliances (not just the PET) had filter cap units applied across the incoming line voltage. Many were three wire types which had a capacitor from phase & neutral to ground called Y capacitors, of the X type are connected across phase and neutral, though if they are placed before the...

Yes it is all over the place on ebay, have a look at this German cable, the label in the photos, they called it a D sub 9: https://www.ebay.com/itm/233540296789? In any case, there is no confusion about the connectors & cables I am referring to now, even if the terminology is all over the place.

Can you lift up the lid of the PET to move the VDU further away from the power transformer and see if that is the cause. After that, if it wasn't, the next thing to do would be to check the power supply voltages for ripple with the scope.