Ok, well, not much to work on - but thanks for helping to at least rule out certain possibilities.
What I see on the Waveform is a type of distortion - almost as if it's either noise, or a reflection - like coax not terminated into a dummy load - a reactive element. It's why I asked those questions about other parts in line to TR17 - if they may have entered in another factor or quirk - to this, and we needed to know they were not adding to the problem.
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So that may mean we need to do some ohmic checks of L6 - make sure it's winds are not broken - that is an open coil and is at the whims of someone careless with a screwdriver, can damage the wires or nick the winds generating a mis-match - mistune problem - even to the point of breaking the slug or case to the point where L6 cannot be used it's too damaged.
So look for physical damage to the work as well as ohmic checks to make sure the winds are ok. This also means using a Loupe - a magnifying glass - to examine the coil up close to ensure it's physically ok.
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...From Harbor Freight...
So if L6 is ok, we also may need to look at what I suggested earlier - remember the S/RF meter?
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Did you even check the rear panel SO-239 to see if it was "Shorted" to case? IF so, you may need to even go back further to L51/L31 combo and check to see if the parts used to "tap" the RF output - are not adding to this - a shorted cap can ruin your day. OR an OPEN connection from one of the Coil winds can also affect the radios ability to receive (and blow up the TX side as well).
If there was a reason he threw it on the floor, you have to review and find out why it got left behind.
Ok, last note about TR17, and why I wanted you to check the board for voltages once the part was removed...
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- Test TR17 - OUT OF CIRCUIT - use any TRANSISTOR tester if possible - get a Hfe number to see if the transistor is still ok.
- Probe the pads - from the foil side, with the Radio powered but into a Dummy load - and adjust RF gain control - does the voltage on the EMITTER side (The L6 side of the RF Amp) show a change?
- Does the Base pad, show a voltage?
- IF Base shows voltage - IS IT LESS THAN Emitter and Collector?
- If not - there's the problem -
- lets' further clarify - open resistor or poor soldering - Base Greater than Emitter?
- R68 needs to be checked for value 2.2K.
- R67 - 820 or 680 ohm resistor - check it's value...
- R66 Needs to be checked for Value 1K.
- Collector "Dead"? L7 is possibly Damaged - see above...
- C52, pulled and checked for value - easier to just replace with a known good part and leave it at that...
- Remove - Unsolder the "tabs" that hold the shield of L7 - to the main PCB and pull of the case exposing the coil - check for damages - Do this also for L8....
- For points of note, the ability of TR17 to "discern" signals in the 27MHz band, note the use of capacitance - two a 0.001uF (102) and a 10pF - both serve to provide a "springboard" or resonance that lets the 27MHz signal float across and have more current applied to get past the Bandpass filter of L7, C52 and L8 - so the IF image from TR18 can discern to a greater degree what is there.
- L6 if "overpeaked" can add more noise - this goes to the "springboard effect" listed above that the capacitance used in the BASE of TR17 uses to develop a resonance effect and amplify a given range of RF - it's crude but effective and the use of L6 for one side and L7 for the other makes this a tank circuit that can self-resonate and blow parts - hence why we are in the mess we have now...
Notice the parts count is getting larger - this is part of the simple fix that a poor soldering job or cold soldering joints tends to create for a Tech that needs to fix a radio known to work ok, but just one day quit. Now we have at least 30 parts involved and that's just to get to TR18.
So this also brings in the variables like RF gain as well as IC 1 - which may be fine just somehow not communicating anymore - so again do your details and make sure the radio and TR17 are ok before you just presume a part failed - for even the most obvious is evident, but may not be the issue - there are too many other parts to interrupt the signal - for if they are ignored then you're stuck in a loop...
(Edits: Gotta' love it when Google changes BCE to ESR...LOL)
