goldscan IV :is there an error/mistake in timing circuit ?

[Max]

Hello Forum,
Just yesterday i have encounter a small problem that i have years ago
in the power supply of the Goldscan and another power supply (based on 7660).
The fact is that sometimes the +5V are absent when you start on the detector , you switch on/off again and the +5V is now ok ...what Happen??? ...i made lot of different PI power supply, but this fail are embarrassing me for years and yesterday i just encounter:
in the gS power it is C8 the value is 100uf it is not good because too HIGH sometimes this value block the 7805 , if you put a 22 o better a 10uf for C8 you did never have this problem...
and this is good for another power supply the electrolytic capacitor before the input of the 7805 must not be very high...
Have all of you a good time,
Alexis.

Hi,
I haven't this problem on mine but could happen due to noise.

If you don't use e.g. 330nF at input and 100nF capacitor at output of regulator you could have troubles in a noisy circuit: the values are from Fairchild datasheets, different ones like both 100nF usually works cool.

This happen easy in digital circuits with lot of digital noise over supply rail, that the device is blocked by a source of noise over the input rail or that the output rail is connected to noisy circuits.

In some schematics , like for GS4, designer forgot that details and used just large electrolitic caps e.g. 100uF good for ripple but not to clean all potential noises entering the 78xx, so better adding parallel 100nF there.

Adding that bypass caps solve the problem in very easy way: try putting two 100nF at input and output, just at solder joints of 7805.

Kind regards,
Max