Alternator Whine, TR-7600/7625                7-9-79


In some mobile installations, alternator whine may be heard during
transmit.  External B+ filtering does not have sufficient effect.

In some instances, using the cigarette lighter will cause this problem.
Running off the fuse block, and even directly from the battery may still not eliminate the noise.

First, check power line routing in the engine compartment.  It should be kept clear of all secondary HV harness wiring, and clear of the alternator, regulator, and ignition primary circuits.  Careful routing should reduce or eliminate noise coming in through the power line.

Check for clean ground connections at the antenna and radio.
Check for clean and tight battery connections.

If all of these measures fail, replace L22 on the VCO unit X50-1580-10 from the original green coil, to either an orange or black coil.  No adjustments should be necessary.

Old part number L40-1021-03 1mH
New part number L40-1021-43 1mH

Please make these changes in your service manual.

JEB/yn
(c) 71079TKC

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SB-045

TR-7600/7625 Audio Tone on TX                8-10-79

Some TR-7600/7625 users report a low background tone during TX, especially noticable at full quieting by the receiving station.

On the PLL unit X50-1580-00, change:

     L18 from 22 uH to 33 uH
     C61 from 22 pF to 33 pF
     C60 from 22 pF to 10 pF
     C42 from 22 pF to 39 pF, or bridge 18pf across foil side and leave original C42 in place.  No adjustment is necessary.

New part:
          L18 33uH L40-3301-03

Please annotate your service manual.

JEB/yn
(c) 8979TKC

-=-=-=-=-

SB-050

TR-7600/7625 Optional Ceramic Filter               8-9-79

Adjacent channel rejection may be improved by changing one capacitor and installing an optional narrow ceramic filter.

On the TX RX unit X44-1320-10, change:

     * L41, CFG-455 F2 to CFL-455F
     * C101, from 470pF to .001uF

Old part L41 L72-0309-05 CFT-455 F2
New part L41 L72-0306-05 CFL-455 F
Please annotate your service manual.

JEB/yn
(c) 8679TKC

PORTED AND REALIGNED FROM PC TO AMIGA FORMAT BY BOB G0LBQ - N6XDI.