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Author Topic: OHR 100 transmitter  (Read 2530 times)
VE3GNU
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Posts: 86




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« on: April 26, 2013, 01:48:04 PM »

Help Wanted!
What's the easiest way to trouble-shoot or check the transmitter of my QRP OHR100 rig?
The receiver works fine, and I hear the CW sidetone alright when I key the transmitter, but no RF out---no voltage out!
Can I assume that the FINAL transmitter is 'shot' or is that too simplistic?
The manual provides no voltage checks on the schematic diagram and no voltage-check chart is available.
Thanks in advance---and much appreciated.
73---Ernie
VE3GNU
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W1JKA
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Posts: 1716




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« Reply #1 on: April 26, 2013, 04:39:05 PM »

FWIW: I had exact problem with my SW 30+ QRP rig.Don't assume it's the final but it's the easiest thing to check out first.For me it was the PA,it was either bad or I shorted it out somehow during construction or alignment,I replaced it and got RF/voltage now working fine.Had same problem in another kit which turned out to be a cold solder joint on one of the toroid coil leads.Basically I just used my VOM and checked for component continuity.
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K0OD
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Posts: 2557




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« Reply #2 on: April 26, 2013, 06:42:00 PM »

Quote
no voltage checks on the schematic diagram and no voltage-check chart is available

You won't find much online either.

My beloved OHR100A's transmitter died several months ago while I was in contact with a DX station. It had some minor problems anyway so I didn't hesitate to send it back to Marshall Emm for a good alignment and repair. His repair tech was ill. A transistor went out. It took ages to get it back, but it works great now. Anything I can hear on my $2800 Flex-5000, I can hear on the OHR!

BTW, just received the DD-1 counter kit--still unbuilt-- and the 10-turn tuning pot which I definitely recommend if you use an outboard audio filter. My tests on the new pot show it tunes better than the stock single turn pot. So you get vastly more bandspread, precise tuning and no backlash. Works fabulously even with my Timewave set to 100Hz bandwidth!   
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AD6KA
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Posts: 2237




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« Reply #3 on: April 26, 2013, 11:05:28 PM »

Had same problem in another kit which turned out to be a cold solder joint on one of the toroid coil leads.Basically I just used my VOM and checked for component continuity.

Beat me to it.

This is the one of, if not the, first places
to check for a cold solder joint in the XMTR circuit.
Lots of time the enamel insulation in the toroid coil &
bifilar transformer wire doesn't quite get completely removed. Sometimes reheating the joint will do it.

Also.....double check that the leads for the bifilar
(and sometimes trifilar) transformers go into the proper
PC board holes. Sometimes those drawings can be confusing,
especially when you are using the same color and gauge of wire
for both the Primary and Secondary.
73, Ken  AD6KA

Good luck and let us know how it works out for you.
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VE3GNU
Member

Posts: 86




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« Reply #4 on: April 27, 2013, 09:58:35 AM »

Thanks to all for your response---but I neglected to mention that the rig has been working FB over the years, and yes---I have the 10-turn pot, as well as the Digital Dial---all in 'good order'. The fact that I can hear the relay of an 'outboard' keyer when I use the hand-key tells me that something is working in the transmitter circuit---I believe---

I just cannot fathom how the transmit portion suddenly stopped working---and the fact that I consider myself somewhat 'technically-challenged'---adds to my dilemma.

The final output transistor is a C2078.

Ernie
VE3GNU
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K0OD
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Posts: 2557




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« Reply #5 on: April 27, 2013, 10:18:24 AM »

Quote
The final output transistor is a C2078.

2SC2078

Also see: http://www.ohr.com/100block.jpg
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