Author Topic: B&K 2040 Repair video  (Read 20928 times)

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Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #15 on: April 02, 2015, 04:28:24 PM »
Ok, I am home. Looks like I had a bad bad scope probe.
Less than a yeaar old too.
See if this looks better.
First is IC308 pin 14. Correct frequency

Second pic is output. Wrong frequency.
Output is a square wave with lots of ringing at 639,9 KHz
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #16 on: April 02, 2015, 04:41:48 PM »
Disconnected the 5 volt rail. Injected 5 volts from an external source. This supply looks a lot cleaner than the 5 volt rail in the 2040. But made no difference in the waveforms. In fact, they were identical.  What I did find was if you drop to voltage below 4.7 volts it shuts off and has no output at IC308 pin 11. These chips like the correct voltage.

Next thing is to recheck the output on my working unit and figure out why I do not have the correct frequency on pin 11.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #17 on: April 02, 2015, 04:51:37 PM »
At this point I connected the 5 volt rail back up. Grabbed the good 2040 and checked the same two locations.
Difference is not much....
Now confused.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #18 on: April 02, 2015, 05:04:56 PM »
Looking for a way to kick myself in the butt!
Cant believe I made such a noob mistake.
Sitting here trying to figure why the output on IC308 is not 064MHz.
Why was I getting 639.999 KHz.
Well there is your answer. Bashes head on work bench till it becomes numb.
NOOB!
Yeah I made a mistake.
Forgets IC308 and moves on.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #19 on: April 02, 2015, 05:52:50 PM »
OK, making more progress. I do not have the correct frequency out of the VCO going into pin 10 of IC303.  So the correct mixing is not there to supply IC303 pin 2 the 6.485MHZ signal. (CH1).
Following the missing signal to IC302 pin 10 takes me back to the VCO again.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #20 on: April 03, 2015, 09:35:11 AM »
Greetings!


I'd be taking a soldering iron to re-heat several joints in and around the power supply connectors in hopes to reduce voltage drop across oxidized contacts...

Regards!
:+> Andy <+:

Thanks for that lesson there Andy. All this IC logic and stuff is really new to me. And I think you hit on a few things that is vital to the operation of these things. I had a friend many years ago that ran an Arcade service.  What he did was buy and rent these to different locations around the county. I would stop in and his dad would be in the back room with a roll of solder and a iron.  I ask what you doing, his reply was "I don't know, this is what they told me to do when these quit".

He knew nothing about electronics but did know he had to reflow solder joints.

Anyway this is why I quoted this part of your post.

As you can see in the pics below the PLL board is not bolted down. Just sits in a foam shell inside the internal RF shield. It has stiff wire connections  that run to feed throughs that lead out of the box. Then there are chokes going to more feed throughs that lead out of the outer box.

While checking a few things I decided to lift the board from is resting place to peek under it. After that I placed it back in and fired it up.
The darn thing started working lol. 
I am able to even reproduce the fault by wiggling the board a bit.  So one of those stiff wires has a bad connection either at the board or the feed points.

First pic is how the board rest in the internal shield
Second shows these stiff wire connections
Third pic is the crystal oven in my newest 2040
Forth pic is the oven in the failed 2040

Next thing to do is re-solder both ends of the connection wires and a few spots on the board. Specially under that oven!.
This should put the unit back in operations.

Since there are no electrolytic on the PLL board I have to pull the audio board out and replace those caps in the power supply. Kind of strange to put the power regulation on the same board as the audio circuits eh?

Then finally reconstruct the oven enclosure. Not sure what type of foam they used here. But it has to be pretty tough not to melt. Well this one did but the other one has not.  When you turn the power switch off the oven stays on.
To keep the temperature stable I have to find something to replace the melted and warped foam with.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #21 on: April 04, 2015, 07:29:30 AM »
Have you seen the Nasa soldering tutorial?
If not should watch it on YT. Takes like 10 minutes to solder one resistor lol.

As far as this 2040 generator? What I think took place some CEO pushed the engineering department to develop this thing taking notes from their older unit they had. But wanted more features.
You think this design is bad, wait till you see my tear down of the GAW cb generator.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #22 on: April 04, 2015, 03:21:56 PM »
Today I spent a little time on the old 2040. First thing I did was remove the PLL board from the unit.  Looks really bad.


On the back of the board someone had did some hack job and installed a frequency expansion.  O removed all the wiring and really hated what was left.

I cleaned up the board, and traces to fin quite a bit of them missing. So after a little work I got them back in the best I could. I used very thin wore and super glued it down to the board.
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #23 on: April 04, 2015, 07:32:25 PM »
Yep, the pads were toast. No way to save what was left on them.  Well, the ones that were left.
I had to get out the video microscope for this one.

One thing you may have not noticed is the entire top surfacew of the board is a ground plane.  You have the traditional traces on the bottom.  But everything on top is at 0 voltage.
I had another one in a year ago that lost RF output.  Through the output stage one pin lost it's ground on the top side of the board. MAn talk about a pain in the rear to trace that out.  Pins grounded on top do not connect to anything below the board.

All connections in and out the RF enclosure uses feed thru caps.
This one is going to be fun.  I have the board out of the box and connected up for testing.
Will post more back later :)
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #24 on: April 04, 2015, 09:46:19 PM »
The saga continues.  A good friend I was in conversation with brough up a good question after I told him there was no output on the mixer IC302. I have a good signal on the input pin 1 of 20.48 MHz. I had already checked the gate of Q307 for a VCO signal. This runs the generator output fruequency when in lock. So if it is not locked the mixer will output the sum of the frequencies.

Anyway I went back and checked pin 10 of the mixer, there was no signal. But yet there was signal at the source of Q307. So for giggles I clipped the output side of C319. Bridged a 4.7pf cap across and bam, the generator cam to life. So for a year and a half C319 has been the smoking gun. And when replace the unit locked.

Still have to address the channel selctor in this unit. No matter where you put it , you get 27.205 on the output.
IC306 and 307 are my first guess, Reason, because there has been previous work under them before, and both are in sockets.

So there you have it folks, you are getting this live as it comes.  And there is more to come...
Buddy kc4umo

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #25 on: April 05, 2015, 07:55:51 AM »
Here is a snippet of the problem circuit. Thought I had attached it last night.

I will post how this works later.
Buddy kc4umo

Offline scootter

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Re: B&K 2040 needs repair help
« Reply #26 on: May 21, 2016, 07:09:00 PM »
I have a B&K 2040 that has been working fine for years, the other day i had a radio on it and noticed that the signal was very weak.  checked coax and radio and they were working good, the 2040 other functions all work good. have printed a schematic for it, just not sure where to start. I can hear the tone on all settings, but its just not very load in the speaker of any radio. I have another 2040 that i would like to get fixed to, if there is some one out there can can fix them and align them, i would be happy to send them out.

Offline The Radio Shop

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Re: B&K 2040 needs repair help
« Reply #27 on: May 21, 2016, 09:50:46 PM »
I have a B&K 2040 that has been working fine for years, the other day i had a radio on it and noticed that the signal was very weak.  checked coax and radio and they were working good, the 2040 other functions all work good. have printed a schematic for it, just not sure where to start. I can hear the tone on all settings, but its just not very load in the speaker of any radio. I have another 2040 that i would like to get fixed to, if there is some one out there can can fix them and align them, i would be happy to send them out.

It is possible you have a shorted resistor (or open) in the attenuator section. This can easily happen if a radio accidently keys up while connected to the generator.

It is also possible that Q312 and Q313 could be bad. These are the output transistors.
Buddy kc4umo

Offline scootter

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Re: B&K 2040 Repair video
« Reply #28 on: May 24, 2016, 09:39:39 PM »
 Thanks! for the help, i have not checked Q312 Q313. But what i did notice is the tin box in side was very hot at one end, opened it up and found that R309, R310get really hot and some of the parts around it. Can't keep it pluged in to long or it gets so hot you can't touch it, not sure if this should be warm or not sence it is a 50 ohm load resister. It has always been pluged in to my 1040.


thanks! radio tech for your help

Offline The Radio Shop

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Re: B&K 2040 Repair video
« Reply #29 on: May 25, 2016, 05:18:15 AM »
Thanks! for the help, i have not checked Q312 Q313. But what i did notice is the tin box in side was very hot at one end, opened it up and found that R309, R310get really hot and some of the parts around it. Can't keep it pluged in to long or it gets so hot you can't touch it, not sure if this should be warm or not sence it is a 50 ohm load resister. It has always been pluged in to my 1040.


thanks! radio tech for your help

Looking at the front of the unit are you talking about the left side that is getting hot?  If so, it is going to be hot. That is the crystal oven.  It gets really hot in that area and keeps the crystals at a certain temperature.
Buddy kc4umo