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Old 17th Aug 2022, 11:27 am   #26
frsimen
Heptode
 
Join Date: Jan 2011
Location: Croydon, London, UK.
Posts: 767
Default Re: Help needed with - Racal Dana 9081

In this circuit, the MC7806P is fed by a 47 ohm resistor. The main current path is via Q1, so the regulator itself may not be that hot even when the current is too high.

Try disconnecting some of the load, you may still have something pulling the supply down.
If you have an oscilloscope, check the ripple on the input to the regulator and the output ripple. The input ripple should be less than 1.3V peak to peak. The output ripple should be no more than a few millivolts.

Table 5-1 shows the expected resistances on the outputs of each of the supplies, which may help identify a problem.

The other voltage readings appear normal, so there is no need to change those regulators. The MC7906P may well be fine too, I wouldn't change it until other avenues have been exhausted. Do check that it is a 7906 and that it hasn't been changed by someone to a 7905, although 4.6V is a still rather low for a 7905.

Paula
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