[Kenwood] TS-850 low sensitivity

Sat, 8 Nov 2003 14:11:31 -0500 (EST)

There are gobs of switching transistors- I emailed FR to see which one he
meant- havent heard yet-
KU4BP suggested to check the .1 cap on the 3100 board- doing that as we
speak-
Henry

On Sat, 8 Nov 2003, Bob Snelgrove wrote:

> Henry
> 
> Could this be it:
> 
> 
> "Low Receiver Sensitivity (from K7FR):  The only failure that I had on
> either of my 850's was that one of the switching transistors that muted the
> receiver during xmit went sour and wouldn't go all the way to cut-off in
> receive. This had the effect of putting about 20dB of pad into the
> receiver. This happened on both. The first one went out to be fixed the
> second one I did myself. 
> 
> Low receiver sensitivity could also be related to the first item on this
> list. Also, I noticed an interesting problem while at W5WMU last time. One
> of the 850s that lives there was down in sensitivity from the one I took
> with me. I am not sure what the problem is, yet. It could be this switching
> transistor problem."
> 
> 
> 
> bob
> 
> 
> 
> 
> 
> 
> 
> At 11:42 AM 11/8/2003 -0500, you wrote:
> >Hello, all-
> >I have been fighting a problem with my high serial # 850 for several weeks
> >now. After combing thru all the archives and a couple emails to Tree
> >concerning things on his website, here's where I am now- I'm hoping
> >someone out there has some more suggestions.
> >After using the rig in WW in a M/S environment, I noticed that sigs were
> >down about 15-20db from an adjacent 850. Especially on the higher bands-
> >(10 was about dead.)Here's what I've done;
> >1. Checked RXb and TXB- rcv voltage is 7.95, and goes to 0 on TX- same
> >with TXB.
> >2. Checked voltages on the SN74LS145 band decoder chip- had some squirrely
> >voltages, decided to replace it, putting in a 16 pin socket for future
> >repairs. Signals on 80 and 40 seemed louder, but still down from the other
> >850. (also did the NB mod by clipping out the caps on the NB board- a
> >dramatic improvement.)
> >3. Tree recommended checking the attenuator circuit- I found that the
> >150ohm R2 on the RF board was open- After replacement, the attenuators
> >work properly. But still low on all bands, thopugh there was some
> >improvement.
> >4. Checked various voltages and diodes, all seemed within tolerance,
> >expect the D31 test point on the rf board, which shows in the service
> >manual that it should be 6.7v on rcvc, 4.8v on TX. Those voltages measure
> >out to 7.4v on RX, 5.6v on TX (both high).
> >5. All 6631 chips are now 66312's (that was done months ago.)I dont think
> >the problem is there.
> >6. I did check the AIP IC on the RF board (the 3900 board)- I found 7.95
> >volts there on pin 4(RXB), but the 12v line is only at 11.5.
> >
> >The big questions- is there a way to boost the RXB/TXB voltage with an
> >adjustment? Does this sound like an RF switch issue?  Source for that 3900
> >board? Never had a DC-DC board changed- Maybe the problem lies there? Any
> >other suggestions welcome. The rig is working much better now, but still 
> >a problem on all bands- still seems to be some sort of attenuation on RX.
> >Still, TX is perfect; full power out, good audio reports.
> >
> >Another week and Clif gets work, but I feel like I'm really close- 73,
> >Henry, W2DZO
> >Winston-Salem, NC
> >
> >
> >- - -
> >
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> >Larry Wilson KE1HZ [email protected]
> >
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> 
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