Obsolete MV5152 LED. Information sought regarding replacement.

[Isobarik]

If the relay coil current passes through the LED, the only way to reduce brightness is to add a resistor across the LED.
Forward voltage drop across an orange LED is about 1.6V, so 100R would bypass 16mA from the LED

Thank you so much for the information David,glad you pointed this out.
Regards
Ray

 

[Isobarik]

Its on the Oscillator diagram Page 7/51. The LED is used in series with a 330ohm resistor and the relay, so its failure will stop the relay operating. As the LED does have to pass a current to energise the relay its possible that the failure is just 'old age'. I would try simply replacing the LED with a modern equivalent, the only problem might be the higher efficiency of a new one
being much brighter. Any LED the correct colour that's happy passing 30 mA (the spec of the original) or more should be fine.
The cost of the LED is so low it's worth trying a simple replacement before digging too deep.
Good Luck, and please let us know how you get on.

Hi Ralph.
You were so right! Brilliant!
I replaced the LED as you suggested and the relay now kicks in.
Can't thank you enough, you've helped me so much and saved me a lot of time trying to fathom out what the problem was.
Slowly but surely I am now getting the B77 in full working order.
Kind regards
Ray

 

[ralphfcooke]

Thank-you for updating us with the outcome; far too often suggestions for fixes are made, but we never find out if they work.
V. happy that a simple fix was all it needed, enjoy your excellent Revox.