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Author Topic: Yaesu FR-101 low gain mystery.  (Read 1241 times)
ZL1BDA
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Posts: 41




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« on: October 29, 2017, 03:07:18 PM »

Good Day all! Well I got a new CIO crystal for the Yaesu and it all installed and calibrated well.
However I now have had a really good look at the receiver and it has a very odd fault. It can detect signals down to 1 uV but it is very lacking in gain.
At first I thought it was a product detector problem, but that was not the case. The strange thing is that the signal is there OK just VERY quiet and the output of the detector shows this on my scope. My thoughts at present are on the IF stages and the Agc system. However while I have a circuit/schematic of this RX, the users manual is very poor on layout. There is apparently nothing like the data available for my Kenwood 820, which is REALLY exhaustive. Does anyone know a source of an actual SERVICE manual for a FR-101? Otherwise I will have to work my way through a lot of stages!!
Regards ZL1BDA ex G3NIA
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AC2EU
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Posts: 1214


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« Reply #1 on: October 29, 2017, 04:35:26 PM »

There is a manual copy here: http://bama.edebris.com/manuals/yaesu/fr101/
But unfortunately it's a poor scan of the original.

Maybe mods.dk has something better?  https://www.mods.dk/

what is the spec for FR101 < 1 uv?
If anything, I would look at AGC first.
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HAMHOCK75
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Posts: 396




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« Reply #2 on: October 29, 2017, 07:19:18 PM »

The FR101 receiver design seems to be very close to the FT101 transceiver receiver. Both have a stated sensitivity of 0.3 uV in SSB/CW mode. I tested my FT101EE's sensitivity. I could clearly hear a 0.1 uV signal from an HP synthesizer in SSB mode. I also tested a Ten Tec C21 CW only transceiver which has no RF stage but has the input signal go directly into a double balanced mixer. I could hear a 0.6 uV signal with the Century 21 about as well as the FT101 at 0.1 uV.
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W2WDX
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Posts: 215




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« Reply #3 on: November 09, 2017, 10:33:26 AM »

There is a series of amplifiers that feed the various detectors from the crystal filters. These are "can" type IC's (CA3053). These are known to go into failure (or become weak) after a time, so I would look at these. These are a bit hard to find these days, since these haven't been manufactured in many years and there are no suitable replacements. And when you can find them they are expensive (if you think $15USD is expensive for one IF IC). Try to source actual RCA branded, there were some very poor unreliable Chinese knock-offs for a while that just didn't cut it (low gain).

However, check these; since it sounds like your problem would be caused by one of them (or both) being weak. One of them also controls the AGC. You can find them on the block diagram (fig 10, page 14 of the Users Manual) right after the crystal filters. They are located on the IF Unit board (PB-1251; Q4 & Q5 I believe). Depending on how early/late your receiver is, sometimes they are on sockets, other times they are soldered.
« Last Edit: November 09, 2017, 10:43:52 AM by W2WDX » Logged

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