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 Post subject: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Wed 13, 2019 2:39 am 
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Joined: Mar Thu 03, 2011 8:53 pm
Posts: 1102
Location: Davis, CA
In the last three or four years, with diagnostic help from several here on the forum, I have had to replace the Q3 transistor in this unit four times. I am using a NTE108 NPN transistor. Any suggestions on remedies to correct this problem?

Thanks, Bob


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Wed 13, 2019 3:59 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 807
I looked over the diagram and there are discrepancies. For instance, the dc conditions on that transistor don't add up.

Having said that, the most power it could dissipate would be in the milliwatts anyway so I don't see why it would fail, unless there is feedback from the load, say you transmitted into it.

Bob


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Fri 15, 2019 12:18 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3912
Location: Florida
Repeated failure says overload of some sort. That transistor type is only rated for 15 Vce. I don't have a schematic. What voltage source is fed to it and what are the normal operating conditions?

RRM


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Fri 15, 2019 9:51 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 211
Location: St. Louis, MO
Seconding overload.

Which revision is yours? There's 2 versions of the schematic out there. It's the last letter of the sheet number for that page. One difference between the two versions is the different supply voltages. Better yet, they reused "10 volts" between the 2 versions. It was the lower voltage in the first schematic and the higher voltage in the later schematic.


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Fri 15, 2019 10:38 pm 
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Joined: Nov Thu 22, 2007 11:31 pm
Posts: 894
Location: Johnston, Iowa
Bob, have you seen this E200D page https://e200d.eqth.net/ Under the semiconductor cross reference link it list NTE109 for Q3.
Keith


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Sat 16, 2019 12:29 am 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 211
Location: St. Louis, MO
keith49vj3 wrote:
Bob, have you seen this E200D page https://e200d.eqth.net/ Under the semiconductor cross reference link it list NTE109 for Q3.
Keith


That's NTE108. NTE109 is for diode D8.


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Sat 16, 2019 3:39 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3912
Location: Florida
If it were mine I'd slap a 2222 in and go from there.

RRM


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Sat 16, 2019 8:40 pm 
Member

Joined: Mar Thu 03, 2011 8:53 pm
Posts: 1102
Location: Davis, CA
Thanks for all the comments.

I use this device for aligning old tube radios. I am totally in the woods when it comes to the technical electronics of this device. I don’t know which version of this unit I have. I think it is the one in the link that Keith posted..

Bob: You mentioned feedback from a load. Is there something I might be doing during an alignment that might be causing failure?

I will try a 2222 next time it goes out.

Bob


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Sat 16, 2019 8:48 pm 
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Joined: Jun Sat 15, 2019 7:43 pm
Posts: 273
I think these may have come from the factory with MPS6507 for Q3

DM


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Sat 16, 2019 8:52 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 807
If you are aligning a transceiver (not a receiver) there is the danger of transmitting into the signal generator. That will destroy some components therein.

I did that a while back and was lucky enough to be able to repair the generator. My generator has reverse power protection but nevertheless had parts burn out and required repair.


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 Post subject: Re: B&K E200D Signal Generator, Frequent replacement of Q3
PostPosted: Nov Sun 17, 2019 9:03 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 211
Location: St. Louis, MO
I remembered something that WoodchuckTN told me here a few months ago. Q3 is a known problem in these particular SGs. Also, my voltages rarely were close to the ones on the schematics.

Going by that last letter of print numbers on the 2 schematics, I call them version B and version H. I can tell you that the one I have was neither, which implies more than 2 versions. Assuming B&K followed the alphabet, that's at least 8 versions out there. As for finding out which version you have, there are some obvious differences. The trimmers on the back of the range switch were machine screws in the earlier versions and ceramic in the later ones. For the attenuator switches, earlier versions were wired point to point, while later ones had a board there. The presence of C55 is another one that's easy to verify with the case off. Is there an electrolytic cap attached to one of the meter screws?

Here are some differences I found:
  1. different power supply values
  2. the value of R2
  3. the presence of R3
  4. resistors in the different bands of the range switch
  5. the crystal calibrator section was reworked. Wires changed, R24 and C21 removed, R59 value changed
  6. the value of R43
  7. the presence of C55


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