REPAIR AND RESTORATION OF THE SR-2000
18
WDØGOF 3/7/20014
4-7. V6 RX FAULT ISOLATION
NOTE: In this next step you will be injecting signal into the plate pin of the tube socket. You will need an
injection probe rated for 300 vdc or higher.
Pull V6, power up and inject 3000 uv at 1650 KHz into pin 5 of
the V6 socket. If you do not get at least ½ watt audio out then L1s5, C59, C60 or FL1 at fault. If you get ½ watt
then V6 or associated circuitry are at fault. If the tube is known to be good then refer to the voltage and
resistance charts in the manual. If the voltages and resistances are correct then suspect C55, C56, C57 or C245.
If all this checks ok then pull V5 and repeat step 6 in the RX FAULT ISOLATION chart (Paragraph
2-4
). If you
get ½ watt audio out then V5 or its associated circuitry are at fault.
SUBSYSTEM TROUBLESHOOTING AND TESTING
4-8. V4A RX FAULT ISOLATION
Assumption: You have injected 35uv @ 1650 KHz into pin 1 of V6 and there was ½ watt audio output. And,
when you inject 100uv into pin 2 of V4 you do not get ½ watt output. Check for 260 Vdc pin 1 of V4. If there is
no 260 Vdc check pin 1 and 2 of T6. The B+ is supplied to V4 through R126 and T6. Pin 2 of V4A should be
zero volts dc in receive mode. If it is a high negative voltage, clean the contacts (pins 9, 1 and 5) of relay K2.
Pin 3 of V4 should have 1.5 vpp RF injection from the VFO and the DC bias should be approximately 11vdc. If
the DC bias is incorrect then either R30 or the tube is bad. If there is no injection RF on pin 3 suspect C53.
4-9. V3 RX FAULT ISOLATION
See note in 4-7
. Pull V3 and check the voltage on the socket pin 6, it should be 260 vdc. If there is no 260 vdc
then suspect T2, C42 or R23. With V3 pulled inject 6.25 MHz at 150uv into V3 socket pin 6. Tune the main
tuning to approximately 250 on the black scale, and peek the audio output. If you do not get ½ watt audio out
then suspect C42, C44 or T2. If the proceeding checks are good there is a bias problem or V3 is bad. If V3 is
known to be good refer to the voltage and resistance charts in the manual to isolate the fault.
4-10 V2 RX MIXER FAULT ISOLATION
See note in 4-7
. Pull V2 and check the voltage on the socket pin 6, it should be 260 vdc. If there is no 260 vdc
then suspect T1, or R16. With V2 pulled inject 6.25 MHz at 25uv into V2 socket pin 6. Tune the main tuning to
approximately 250 on the black scale, and peek the audio output. If you do not get ½ watt audio out then
suspect C30, C31 or T1. If the proceeding checks are good there is a bias problem, injection problem or V2 is
bad. If V2 is known to be good refer to the voltage and resistance charts in the manual to isolate the fault. If the
tube voltages and resistances are good check the mixer injection voltage. Pin 7 of V2 should have 1.5 vpp at
approximately 4.600 MHz.
4-11 V1 RX FAULT ISOLATION
See note in 4-7
. Pull V1 and check the voltage on the socket pin 5, it should be 260 vdc. If there is no 260 vdc
then suspect L6. With V1 pulled inject 7.25 MHz at 45uv into V1 socket pin 5. Tune the main tuning to
approximately 250 on the black scale, and peek the audio output. If there is no or weak audio output then the
fault most likely lies in the band coils and trap from C10 to C25. If there is audio reinstall V1 inject 0.5uv @
7.250 MHz into pin 1. CASE 1, you get week audio suspect R3 R7 R5 R4A dirty contact on K2 contacts 3, 7,
and 11.