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Radio Head Unit - Repair III

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.. continuation of Radio Head Unit - Repair II

CD port not working
Observed on: 1 EUDM Radio
Fixed by: PCB repair, replacement of OP amp

State: Fully understood

Acid damage to the traces around the CD port OP amplifier can cause the connection to the CD changer to fail.

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severe trace damage around the CD port OP amp mounting point

The CD port should be removed and cleaned. In addition to repairing the broken traces, all VIAs in the area should to be reinforced by soldering a thin wire through them. The OP amp usually requires replacement, too.

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repaired area with new OP amp

The original OP amp, especially in it's metric size packaging, is no longer available but can be replaced with a standard SMD 4580 dual OP amp from JRC or NJM when carefully placing it on the existing connection pads.

Intermittent complete loss of sound

Observed on: 1 USDM Radio
Fixed by: PCB repair, replacement of flex cable and flex cable connector

State: Fully understood


Acid damage to the flex cable connectors causes intermittent connections. Such contaminated connections can be identified by a greenish colour visible on the flex cable and/or the connector:


green stains on the cable


a contaminated connector

Measuring the connector's pins against each other (after removal from the PCB) showed resistances of less than 200 kΩ - in an OK connector they should be >2 MΩ. Replacement of the connector and flex cable is required. Acid-affected areas on the PCB need to be cleaned-up, too.

Intermittent complete loss of sound II
Observed on: 1 EUDM Radio
Fixed by: PCB repair

State: Fully understood


A previously repaired radio, working fine for a maximum of 5-20 minutes, followed by complete loss of sound. The 10 V supply dropped from 10 V to 3.9 when the audio stopped.

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some chips with 10 V supply (V+): IC206, IC205, IC307, IC304 and IC305 (not seen above)

Most operational amplifiers on the PCB depend on 10 V and a drop affects the whole audio path. Below circuit shows that enabling the 10 V supply requires battery voltage to be present on the B.T.T. pin as well as +5 V on the PCNT pin of the main flex cables. The voltage is created by the Zener diode ZD807 and needs to show a correct 10.8 V when the radio is switched on.


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10 V power supply switching and routing

A broken trace caused the voltage not to reach the amplifier chips. Below (yellow) repair trace connects the output of ZD807 to V+ of IC205 and restores full functionality.

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the yellow repair cable restores the 10 V supply




Channel loss or distorted sound from CD changer
<TBD>

Volume control needs "Warm-Up" to work normally
<TBD>

Updated 21-01-2024 at 07:15 PM by Heineken

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  1. Heineken's Avatar
    Added Information about Intermittent complete loss of sound.
  2. Heineken's Avatar
    Added information and schematics on Intermittent complete loss of sound II.