Maycom em27 CB Radio

[JimB]

Looking at this:
**broken link removed**
it does show a battery/capacitor near the 7805 regulator.

Looking at the schematic, on the output of IC300 is the diode D304 which feeds the line BACK-UP B+ .
There are two capacitors C316 C317, my best guess is that the backup battery or capacitor is connected at this point in parallel with these caps.
Diode D304 is there to stop the battery/capacitor discharging back through IC300 when the main power is off.

I can still only see 2 regulators!!

Yes, you are correct (I think).
But there are numerous transistors Q300 to Q313 (ish) which are used as part of the switching for various functions, (transmit/receive etc).

JimB

 

[large_ghostman]

Hi Jim, alot of the newer radios have caps as back up (newer being relative!) I wonder if the drawing is showing the backup as caps?? I will get it back out later and have another go, I also have the camera for today .

Some of the transistors look like they were de soldered at some point .

 

[large_ghostman]

FIXED!!! great call Jim it was one of the Regulators! I have another of these radios (actually I think there is 4 all together), I will dig that one out later and take a look. At least I now have a unit I can mess with and if it survives I can sell it on.

I have replaced the battery with a 1f super cap from a sil labs badgerboard.

 

[large_ghostman]

Havnt found the other one yet, this is the first time I have come across a dead regulator, I am surprised it didnt take more out with it seeing as they have 13.8V going into them.