22 Jul
2012
22 Jul
'12
9:51 p.m.
I checked out the power supply. It's basically a common-base amplifier with a 5.6v
Zener diode. It doesn't have a full-wave bridge rectifier. Theres a 4,000uf
electrolytic capacitor for filtering the input to the transistor. Given the design,
I'd expect it to be pretty sensitive to problems with that capacitor. If I have a
suitable part, I think I will replace the transistor and the diode with a proper 7805
regulator.
Sent from my iPad
On 2012-07-22, at 10:35 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
On 2012 Jul 22, at 2:37 PM, Paul Anderson wrote:
I'm currently working on restoring a NRI 832
computer trainer. I finally got my oscilloscope on it. It looks like the clock isn't
running. You can see the waveform in this video. I tried both the fast(250kHz) and
slow(2Hz) clock. I'm just seeing noise from the power supply.
http://www.youtube.com/watch?v=RBV4QgQHq98
From your video, with 0.4V of 120Hz ripple on a clock output, you might back up and
check/measure/scope the power supply, look at what's going into the regulator and
what's coming out.