๐ธ๐ฐ Tesla PMD 85: Part 5 (PMD 85-2B)
22The first attempt to power up my 2B version - this has 64KBytes (8 x 64Kbit) DRAM instead of 48KBytes (24 x 16Kbit), using beautiful ceramic Soviet ะ565ะ ะฃ5ะ 64Kbit chips compared to Western Mostek 4116 16Kbit chips.
I also tried using the PMD 10 power supply - the green power LED wasn't working so replaced it with a "modern" blue one.
Got a similar TV output as my other computer so tried a 100ยตF capacitor across the video output as suggested by @jjermar1. The picture did change, maybe some distorted text now (?), so perhaps I need to try with a proper CRT?
Doh - I just realised, I've got that handheld Sony B&W CRT ... although I don't have a plug for its baseband input ...
Whilst fiddling with that the power supply failed. Both the fuse (2.5A 250VAC) and a safety capacitor (combined class X2/Y) had failed. The safety capacitor, a "Miflex KSPpz-6", is rated at 100nF/0.1ยตF Class X2 and 2x2.5nF Class Y.
However, what I found a little confusing is that it was only connected across the Active & Neutral lines for Class X protection ... it should've had a third wire to earth for the Class Y protection (I think).
Example of the RIFA combined Class X/Y capacitor in the Grundy NewBrain's PSU:
https://youtu.be/o2jY8LM2JLk?si=ZaDJcjxEN42czrHX&t=402
When I look closer, the third wire is actually cut off! So I really just need a Class X2 replacement.
I do have replacement 100nF Class X2 capacitors but these are in rectangular cases. Ideally I'd replace it with a cylindrical, radial capacitor. Searching for them shows plenty available (in Europe) so it shouldn't be too hard to get a replacement.