(28-11-2025, 12:39 PM)The_Huck Wrote: I'm going to apply what I learn here to help fix up a dead Dick Smith Wizzard and a couple of IBM PC boards.

(28-11-2025, 12:39 PM)The_Huck Wrote: When powering from my bench supply set to 12V, I get 11.5V on pins 1 & 2 and at the input to the voltage regulators, and 5V on the regulator output. The computer is consuming around 920mA.

(28-11-2025, 03:13 PM)MbeeTech Wrote: If you are still getting a low on pin 18 of the right hand 25 way pin strip (pin 1 is at the back of the machine, pin 25 towards the front, then have a look at both C43 (0.68uf) and C52 (2.2uF) on the coreboard.
After half a second or so of power on, both of these should have close to 5v on their +ve terminal.  C43 in particular is notorious for failing at this age. If you see either of them showing a voltage of less than 4.0v
then replace them as they have broken down and have a low internal resistance.  The values are not critical, and you can replace them with tantalum or electrolytic parts rated at 10v or greater.
Eg, for the 0.68uF you can use a 1uF - it will just mean that you have to hold the RESET key down longer when you want to reset the machine.

(28-11-2025, 03:59 PM)CheshireNoir Wrote:

(28-11-2025, 12:39 PM)The_Huck Wrote: I'm going to apply what I learn here to help fix up a dead Dick Smith Wizzard and a couple of IBM PC boards.

OMG! You have a Wizzard as well? There's not many CreatiVision / Wizzard owners out there :-)

(I have done a lot of stuff with the Wizzard over the years. Currently working on a replacement controller for them as the membranes in them are terrible)

(28-11-2025, 12:39 PM)The_Huck Wrote: When powering from my bench supply set to 12V, I get 11.5V on pins 1 & 2 and at the input to the voltage regulators, and 5V on the regulator output. The computer is consuming around 920mA.

12V will run the regulators pretty hard. I find around 10V is the "sweet spot", at least for me.

Getting that reset working will be the big first step. What happens if you manually reset it? (Try holding down the RESET key on the keyboard for a few seconds.)

Cheers!
John

Quote:I swapped out C52 and now I'm getting a high on the reset line.
Should I swap out C43 or is that okay?

C43 was at 4.7v and C52 is at 2.2v. 

(28-11-2025, 04:56 PM)MbeeTech Wrote:

Quote:I swapped out C52 and now I'm getting a high on the reset line.
Should I swap out C43 or is that okay?

C43 was at 4.7v and C52 is at 2.2v. 

I'd leave C43 - it seems o.k.  C52 was the culprit.

Now you can check the address, data & control lines to see what action you have.  Check the ROM Chip select as well, to see if it cycles up from address 0h to 8000h where the boot rom sits in memory.

The preferred input voltage to the computer is 10V but it will work down to 8v o.k.  12v is acceptable, but it has to disipate more heat out of the 7805 regulators.