The zeners and power jack socket should be arriving today. I have some vero board I can use to make up the little PCB for the (7.5V) power distribution, three zeners, diode to stop the Mac Portable trying to back-power the unit if the power's switched off, oh and connecting the ammeter. Once I've w...

stephen_usher wrote: ↑Thu Apr 11, 2024 9:29 am Oh, that's so much more usable.

It is isn't it

A quick aside, one of the guys over on Osiweb.org has created a new monitor ROM that allows for 48 columns as well as 24, selectable at boot time. As well as the new ROM, there is a small bodge, represented by a jumper wire here: IMG20240411085229.jpg And the results are great: IMG20240411085334.jpg...

WOW!!!

stephen_usher wrote: ↑Wed Apr 10, 2024 2:48 pm Sounds like something isn't clocking in the data on the 74LS76, or the clear is being kept low. That would be my next point of investigation.

I did check all the inputs and I'm sure clear was OK, but certainly worth another look.

How are you getting on with the tape interface? Well, not got any further, I replaced the IC but no different. I lifted a leg of the cap and no difference, and the cap was the right value. I also lifted the leg on the resistor before the cap and the value is correct and with the leg lifted the sign...

Yeah, three 5W Zeners is 15 watts, that's over 2 amps at 7.5V. The current limiter would kick in well before that and bring the voltage down. Therefore three Zeners is overkill a bit but it's best to engineer for the worst case. Belt and braces is always a good plan. Under test with the bench power...

So what does the 1.37 represent? Amps? Yes, that's what the bulb is drawing. I don't like the regulation, it's a bit pants. As the load decreases the voltage goes up, levelling out at just under 9V. I think I'm going to have to put a large Zener diode clamp into the circuit to keep it stable, or ra...

The Direct from China eBay variable step-down regulator with current limiter arrived today. Of course, no instructions so getting the voltage to change etc. was very much trial and error. Anyway, it does work: IMG_3672.jpeg I have it on test at the moment. The regulation isn't massively great as th...

Hi @rubber_jonnie Sorry no bench PSU available. I heard very good things about the meanwell PSU and can buy here in Germany for about 15 Euro, so may give it a shot. What about the blown capacitor on the mainboard in modulator section please? Wise to recap the whole board as there are almost 20 cap...