Background: I am a still-learning hobbyist, but I have very nice lab equipment. PSUs, Freq Gens, Freq Counters, Scopes, Mutlimeters, Soldering Stations, etc... So, if you can tell me what to test, I can tell you what I find...
I am wanting to repair this clock for the learning experience. Yes, I know a new clock would be the better investment, so, let's stick with discussing the repair, please and thank you.
This is a very minimal circuit... I have only started my investigations, but I am only finding...
- a 120 to 4.7VAC-0-4.7VAC transformer to a couple of rectifying diodes... No voltage regulator
- the LM8560 takes its timing from the 60Hz mains AC. The is no external oscillator can.
- various other diodes, resistors, caps, inductor, etc., but no transistors. I replaced the 330uF e-cap with a 470uF (what I had in stock,) just as a matter of maintenance. The 330uF tested as good. The LM8560 data sheet spec's a 470uF e-cap. This did not improve the display brightness.
- I do have 10.87=11.00VDC fluctuating on the LM8560 supply pin, with 0.47VAC. This chip runs on -15V to +0.3V, so I probably had my meter probes inverted.
The minimal components seems to be in keeping with the DS common circuit diagram. See attached.
I think this chip is meant to drive a common cathode display. So, what might cause the display to dim, equally, over all the digits?
Thank you for your help.