[Kenwood] TS-850 low sensitivity

Fri, 7 Nov 2003 16:51:28 -0500 (EST)

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