Troubleshooting - Acom 1500 Manual

The swamping resistor Rsw is a termination load for this circuit and can dissipate up to 100W of RF
drive power.
Cathode resistors labeled Rc create DC and RF negative feedback, thus stabilizing the gain and
equalizing the frequency response. The varistor VSsg, in the screen grid circuit protects the tube and
the screen grid voltage regulator in the event of an internal tube flashover.
The combination noted as Lp1-Rp1 in the plate circuit is a VHF/UHF parasitic suppressor. DC plate
voltage is fed through chokes RFC1-RFC2 and the capacitor Cb3 blocks it from the output. The output
circuit consists of LP1, LP2, LL, CP1-CP3, and CL1-CL3, which form a classic Pi-L network to
suppress any harmonic frequency emissions. This tank is switched and tuned by S1A-S1C and the air
variable capacitors CP1, 2 and CL1, 2. The output signal is fed through an additional VHF low-pass
filter for frequencies above 55MHz (Lf1, Lf2 and Cf). Then it is passed through the vacuum antenna
relay K1, wattmeter current transformer TA1, and a high-pass filter RFCasw-Casw for frequencies
below 100kHz, to the antenna switch and the three outputs. The chokes RFC3 and RFCasw keep
track of the antenna relay contacts and together with Casw prevent the plate supply voltage from
reaching the antenna. The RF choke RFCasw shunts the high voltage to ground should the DC
blocking capacitor Cb3 fail. The resistor Rasw protects the amplifier from electro-static energy from
the antenna.
The PLATE CAPACITIVE DIVIDER and RF WATTMETER are the main sources of information for the
control circuit of the amplifier during the antenna impedance matching process. The control circuit is
based on the 80C552 micro-controller from Philips.
All supply voltages are delivered from the MAINS&LOW VOLTAGE and HIGH VOLTAGE SUPPLY
PCBs. The control grid, screen grid, and plate currents, plate cooling airflow temperature, reflected
power, etc. are continuously monitored.
information.
* Detailed electrical schematic diagrams are available from ACOM or from your dealer on request.

6-5. Troubleshooting

See S.5-4 for the method of reading the auto-protection signatures. You can decode them using the
information below.*
The signatures are structured in two lines, three groups by six symbols for every one event of auto-
protection. The last event is numbered as 1A-1B pair of lines, and the oldest one is 7A-7B.
The meaning of the first group is as follows:
a) nA - the number of the trip;
b) Next three symbols mean the following:
PN0 - tests made during Power-On procedure, before HV is ON;
PN2 - tests made during Power-On procedure, after HV is ON and one second after step-start is
closed;
SB0 - tests made in Stand-By, during the warm-up period or while entering Stand By (from
Operate);
SB2 - tests made during Stand-By, after the warm-up period;
PR0 - tests made while entering Operate;
PR2 - tests made during Operate;
TR0 - antenna relay tests made while changing from Tx to Rx (during Operate)
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Many software-derived protections are based on this