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IC-271A/H: most common service | Radioaficion Ham Radio

IC-271A/H: most common service

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Most Common Service Questions for the Icom IC-271A/H

Symptom: "Rushing water" or "aurora" sound in FM receive audio. SSB sounds raspy and distorted.
Probable Causes: 1) Bad plastic trimmer capacitors on HPL unit. 2) Old, dried out electrolytic capacitor C2 on HPL unit is allowing regulator to oscillate.
Cure: Replace faulty trimmers C16 and C78 on HPL unit with ceramic versions. Replace C2.
Remarks: To allow proper alignment of ceramic trimmers, reverse values of C16 and C78: Make C16=12pf, and C78=6pf

Symptom: Frequency instability
Probable Causes: 1) Bad plastic trimmer capacitors in HPL unit. 2) Bad solder at IC2 regulator on HPL unit.
Cure: Replace trimmers as stated above. Resolder cracked joints at regulator.

Symptom: No RX/TX, or no RX/TX when unit warms up. Unit may have dead spots in tuning range. Inspection reveals that the HPL loop is unlocked. Trimmer capacitors on HPL unit have already been replaced.
Probable Causes: Bad C9 on HPL unit.
Cure: Replace C9 (luF, 50-volt) BP capacitor on HPL unit.

Symptom: No Frequency display, only decimal points. Problem may be intermittent or temperature related.
Probable Cause: Display DC-DC converter has noisy output.
Cure: Replace all of the following dried-out electrolytic capacitors on the display unit: C3, C6, C7, C8, C9, C10, C11, and C14. (These capacitors are dark light blue when they are new. Capacitors that have turned gray are old and dried-out.)
Remarks: While servicing the DC-DC converter section, look for cracked solder joints as this section of the radio tends to run hot. Also, we recommend reprogramming the RAM card after servicing the DC-DC section.

Symptom: Erratic display i.e., frequency listed will be out of the normal operating range of the radio. Rotating the VFO knob may cause strange characters to appear in the display. Cycling the power switch a few times may restore operation temporarily
Probable Causes: 1) Cracked solder on RAM unit is causing logic errors. 2) Program in RAM unit is corrupted. 3) IC21 regulator on logic unit is producing noise or oscillating.
Cure: Replace filter capacitors C11, C26, and C26 on logic unit if they appear overheated or dried out. Resolder cracked joints at J1 and J2 connectors on RAM unit, then reprogram. If this does not help, substitute RAM unit with a known good one. If the RAM unit does not cure the problem, there may be noise from the DC-DC converter causing the logic unit to glitch. Follow instructions for the previous problem.
Remarks: While servicing the DC-DC converter section, look for cracked solder joints as this section of the radio tends to run hot. Also, we recommend reprogramming the RAM card after servicing the DC-DC section.

Symptom: Intermittent RX/TX. May have dead spots in tuning range.
Probable Causes: Bad Data to HPL unit.
Cure: Resolder joints at J11 on logic unit. Resolder other suspected poor joints on logic unit. If this does not help, there may be a problem with RAM unit or associated circuitry. (See previous listed repair)

Symptom: CPU noise in audio
Probable Causes: Poor ground on display unit
Cure: Tighten the screws that hold down the display unit PCB. If this does not help, install a plastic-coated metal shield over the display unit. (This type of shield is available through our parts department).

Symptom: Loud, high pitched-squeal emanates from inside radio.
Probable Causes: DC-DC converter transformer has a loose core.
Cure: Replace T1 (T0-9) on the display unit

Symptom: Very Low RX sensitivity
Probable Causes: Bad Q7 on YGR unit.
Cure: Replace bad Q7 (2SK125).

Symptom: No RX. Investigation reveals that T/R relay (RL1) on filter unit does not release in receive mode.
Probable Causes: Leaky Q39 on main unit.
Cure: Replace leaky Q39 (2SC2785).

Symptom: Drastic change in audio frequency response between USB and LSB., i.e. USB audio has too much bass while LSB audio has too much treble. TX frequency response is also poor
Probable Causes: Misadjustment of the BFO or a faulty crystal filter.
Cure: Realign the BFO. If this doesn't help, then the problem is most likely a bad FI-1 on the main unit (10M24D4).

Symptom: VFO tuning is erratic. Sometimes frequency doesn't increment steadily when VFO knob is turned.
Probable Causes: Dirty rotary encoder.
Cure: Remove white plastic cover from back of rotary encoder and spray-clean the carbon track with Blue Showers solvent. Spin VFO know vigorously while spraying.
Remarks: Do not let solvent saturate the display unit or allow it to come into contact with the plastic display lens. Stuff a paper towel between the rotary encoder and display unit to catch spray run-off

Symptom: In 271H, low TX power output with high current draw from the power supply.
Probable Causes: Bad C28 chip cap on PA unit.
Cure: Replace C28.
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