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Old 01-19-2011, 11:30 AM
Radio Tech Radio Tech is offline
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Now, what to do now eh?
You are probably thinking "thats not much to go on, you left out half the radio".

Well, yes and no.
This is the basic workings of a receiver and transmitter. If you will take the block diagram, the schematic, and the above info, you will see a whole bigger picture. But we are only starting with the basic radio.

It's the difference in knowing how to fix a radio or being a parts changer by the "shotgun approach". What is the shotgun approach? It is going in and changing parts without forst determining what is and what is not working. A lot of times you get lucky and replace the bad part. Most of the time you end up throwing the rig to the side.

The big three.
Radio may light up.
But has no transmit and no receive. That is what we call a dead radio.
Radio transmits but has no receive, Dead receiver.
Radio receives but has no transmit. Dead transmitter.

By using the above info you should be able to determine the problem in a matter of minutes. By process of ellimination.
Find the stages that are working. Then elliminate each one.

Again, this is where your test radio comes in handy.
Dead radio. Do you hear anything in the test radio when transmiting? Or hear anything in the receiver while transmitting on the test rig?
The most possible cause of a Dead radio is the PLL and voltage rail.

The dead receiver or dead transmiter can also be caused by a missing voltage but maily one of the mixers or OSC not working.

Weak receive can possibly be TR & bad or the protestion diodes just ahead of TR 7 bad. This happens when the front end is over loaded by strong signals such as some one keying a big amp up. Even static electricity on the antenna can take these devices out.

No output but can hear a 27 mhz signal in a test radio can tell you the final, driver , or prediver is bad. A completly dead transmitter can be as simple as the TX mixer has gone bad.

Other circuits we will discuss is :
RF Gain
Squelch
NB/ANL
AGC
Audio Circuit
Phase Lock Loop
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