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B&K 2040 Repair video

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The Radio Shop:
https://www.youtube.com/watch?v=HO_nYitbozU&feature=youtu.be


https://youtu.be/HO_nYitbozU

KC4UMO:
Here the the circuit that is bad.

The Radio Shop:
The next 2040 I am going to attempt to fix is in bad shape.
The first issue is the PLL is not operating properly. Very little signal out and it does not change when you select different frequencies.

First thing we will do is check the power supply and verify we have the correct voltages.  Since the 74xx chips needs 5 volts to operate we will have to verify that they are spot on and have little ripple.

The Radio Shop:
Another 2040 here in the shop has bit the dust. This is the one I repiared the meter error months ago.
It has the deaded PLL unlock symptom. You turn unit on set to generate and the radio under test hears nothing. A few minutes later the radios hears a signal sweeping the band. So the PLL is running wild and is not locked on one frequency.

My weakness in radio has always been the PLL circuit.  So I have a lot to learn. There has been others that have helped me through it to understand more about how PLL works. The PLL in these type of generators are a bit different than you ham or cb radio. These unit run a 27 MHz signal at the VCO's output.

The stock service material available for the 2040 is not bad. However they did not give you a block diagram, there are no frequency path on the schematic, and most circuit blocks are not labled what they are. There is a copy of the manual with some of this info available. The stock manual does provide a voltage chart.

So at the momnet I have 3 of these units. My 2040 on the main bench is in pretty good shape and works fine. Now the unit on my other bench has failed. This one is the one I replaced an opamp in and is a very clean and has never been worked on that I can tell. The third unit is one I bought that was non working. Someone had modified it for extended frequency coverage. Has a lot of hack jobs done to it but it is doing the same as the other unit.

So what I am going to do is take my working unit and open it up. Go through it with a volt meter and scope noting readings onto the schematic.  In all hope we can find out more of what goes on in these old test gear.

The Radio Shop:
The manual listed below is the one that has the circuit lables. It is what I will be using to make the test notes.

I like all that want to join in please do. But lets keep the thread on topic please.

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