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                        Kenwood Service Centers

   Kenwood Service Corporation             Kenwood Service Center, East
   2201 East Dominguez Street              829 Lynnhaven Parkway, Suite 130
   Long Beach, California 90801            Virginia Beach, Virginia 23452
   Telephone 1-310-639-5300                Telephone 1-804-340-1702

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BULLETIN # 974
MODEL: TS-440S
SUBJECT: PLL UNLOCK DUE TO VCO #1

The TS-440S Control unit supplies band information to four circuits in 
the transceiver. The circuits are the receiver front end Band Pass Filter 
(BPF), the antenna tuner (AT), the transmitter Low Pass Filter (LPF), 
and the VCO circuits on the RF board that are part of PLL #1.

There are ten receiver front end BPFs that are diode switched into 
operation. If one of the diodes (D4-D23) becomes shorted or leaky, 
the band information is felt at two BPFs at one time. The voltage going 
through the bad diode will loop back to the VCO circuit, antenna tuner 
circuit, and LPF circuit.

The unwanted voltage will then create one or more of the following symptoms:

A. PLL unlock (the transceiver only displays decimals).
B. No antenna tuner operation.
C. Low receive sensitivity.
D. Low or no transmit power output.
E. Distorted transmit audio.
F. RF feedback.

The most common symptom is PLL unlock. To test the diodes, remove the 
large shield on the RF board to expose the BPF circuits. Reset the 
transceiver by holding in the A=B button as the power is turned on. 
Even if the display only shows decimals, only the BPF for 14MHz should 
be turned on. Using a DC voltmeter, measure the voltage at coils L11, 
L15, L21, L28, L34, L40, L46, L52, L58, and L62. Only coil L52 should 
measure 8VDC. The other coils should read 0VDC. If one reads 0.5 - 8VDC, 
replace the two diodes in that BPF circuit.


COIL/DIODE/FREQUENCY RANGE RELATIONSHIP:

L11 D4	D5	0-0.5MHZ 	L15	D6	D7		0.5-1.6MHZ
L21 D8	D9	1.6-2.5MHZ	L28	D10	D11		2.5-4MHZ
L34 D12	D13	4-6MHZ		L40	D14	D15		6-7.5MHZ
L46 D16	D17	7.5-10.5MHZ	L52	D18	D19		10.5-14.5MHZ
L58 D20	D21	14.5-22MHZ	L62	D22	D23		22-30MHZ

REPLACEMENT DIODE PART NUMBER:

1S2588 OR 1SS91S:	D4, 6, 8, 10, 12, 14, 16, 18, 20, 22
BA282			D5, 7, 9, 11, 13, 15, 17, 19, 21, 23


Time required to perform this repair is 1 hr. or less.