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Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images

Kob82 13398 13
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  • #1 16865258
    Kob82
    Level 9  
    Hello, I have a problem with the Bosch GML 20 radio, so this is how the radio turns on, everything works except the sound, it works on the headphones, but you cannot increase it very quietly, although the voice control on the display increases and decreases. I am adding a photo of the PCB with speaker terminals, if someone would advise me how to fix it, I would be grateful, thank you in advance for the answers.
    Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images
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  • #2 16865307
    SERVICE-AV
    Level 39  
    Without knowledge of electronics, you can not move, tell someone what he does professionally or set up an advertisement I am going to repair.
  • #3 16865625
    Kob82
    Level 9  
    I just wanted to find out what could have been damaged on the plate from the photo
    and possibly where to fix it and at what cost.
  • #4 16866080
    398216 Usunięty
    Level 43  
    Kob82 wrote:
    what could have been damaged on the plate from the photo

    Without p
    Kob82 wrote:
    zenia, or even a cursory "glance" at this equipment (but in real life, the photos may not be quite useful here), it is not possible.
    [quote = "Kob82"] where to fix it

    On the radio and television service?
    Kob82 wrote:
    at what cost.

    You will find out on the spot. Without a diagnosis (I wrote above) it is impossible, besides, each website has its own prices.
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  • #5 16871211
    Micek64
    Level 18  
    Do you know more about this fault?
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  • #6 16872538
    Kob82
    Level 9  
    I gave the radio to a colleague who deals with car electronics, his diagnosis shows that the SMD TAS5706B chip, the so-called power amplifier, is damaged, a fairly popular fault in these radios, if the ordered part arrives, I will take a few photos of the soldering process.
  • #7 16873272
    Micek64
    Level 18  
    OK, I will be grateful for the report
  • #8 16901425
    maniek1603
    Level 1  
    Hello, the power amplifier is not always to blame for this, it may turn out that something else has been damaged and the TAS system is good.
  • #9 16902607
    Micek64
    Level 18  
    Therefore, I am still waiting for the final of this action :)
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  • #10 16945504
    Micek64
    Level 18  
    To the author of the topic: is something already known?
  • #11 17109842
    fellowes20
    Level 19  
    Hello colleagues. If you have not solved the problem with this equipment, I advise you to check the PCM1808 analog-to-digital converter on the amplifier module, I already got 3 pieces for repair and they all had the same replacement and it flashes.
  • #12 17126605
    Kob82
    Level 9  
    Hello, I am sorry that I did not speak for so long but I had an urgent departure, but to the point the radio, of course, was the fault of the PCM1808 digital anologically repaired system. Of course, the radio worked for a few days during the tests and then it turned out that the TAS5706B power amplifier was also damaged, I do not know how many cases, but a short circuit in the PCM1808 circuit also damaged the TAS5706B circuit. So, to be calm and enjoy the radio, I would advise you to replace the systems marked in the photos, the repair of the radio was PCM1808 - 5 pcs - 30 PLN, TAS5706B - 1 pcs - 50 PLN. Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images b.jpg [/ img] [/url]

    Added after 7 [minutes]:

    I brought another radio from abroad and I have a problem with the power supply, maybe someone will tell you where I can find a transformer like in the pictures. After disconnecting the wires from the board, the transformer has a short circuit and heats up quickly and the fuse blows. Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images Bosch GML 20 Radio Problem: No Sound, Low Volume on Headphones & Speaker Terminal PCB Images
  • #13 17126852
    398216 Usunięty
    Level 43  
    From what I can see it may be a transformer from the St-By system. It should be around 3-5W and voltage around 8-9V. What kind of radio is this?
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Topic summary

✨ The Bosch GML 20 radio is experiencing sound issues, functioning only at low volume through headphones while the speaker output remains silent. Initial diagnostics suggested a potential fault with the SMD TAS5706B power amplifier. Further investigation revealed that the PCM1808 analog-to-digital converter was also defective, which is a common issue in these radios. The recommended repairs include replacing both the PCM1808 and TAS5706B components, with costs estimated at 30 PLN for the PCM1808 and 50 PLN for the TAS5706B. Users are advised to check both components to ensure full functionality of the radio.
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FAQ

TL;DR: Bosch GML 20 with no sound? In 3 documented cases, “check the PCM1808 analog-to-digital converter” first; it’s a recurrent fault that can mute audio. Some sets also need the TAS5706B amp replaced. [Elektroda, fellowes20, post #17109842]

Why it matters: This FAQ helps DIYers and technicians quickly diagnose no-sound/low-volume issues on Bosch GML 20 and estimate repair parts and steps.

Quick Facts

How do I fix a Bosch GML 20 that powers on but has no sound?

Start with the audio path. Replace the PCM1808 ADC on the amp module, then verify/replace the TAS5706B power amp if output is still muted. One report fixed audio after new PCM1808s but later required the TAS5706B as well. Use proper SMD rework and test speakers and headphones after each step. [Elektroda, Kob82, post #17126605]

Is the TAS5706B always to blame for no sound?

No. As one technician notes, “the power amplifier is not always to blame.” Diagnose the front-end first, especially the PCM1808 ADC on the amplifier board. Swap parts only after confirming rails, clocks, and I2S lines. [Elektroda, maniek1603, post #16901425]

What symptoms suggest a front-end (PCM1808) issue on the GML 20?

Typical signs include no speaker output, headphone audio present but extremely low, and the on-screen volume bar moving normally. This points to digital audio path or ADC issues rather than user controls. Verify with known-good headphones and inputs. [Elektroda, Kob82, post #16865258]

Can a failed PCM1808 damage the TAS5706B amplifier?

Yes. A short within the PCM1808 circuit can also take out the TAS5706B, leading to complete speaker silence. Replace the PCM1808 first, then recheck speaker output; if still dead, replace the TAS5706B. [Elektroda, Kob82, post #17126605]

How much do the parts cost, and how many PCM1808s might I need?

One repair used 5 PCM1808 chips (≈30 PLN total) and one TAS5706B (≈50 PLN). The batch approach helps when multiple ADCs test marginal or when stocking spares. That’s a concrete 5-piece statistic from a successful repair. [Elektroda, Kob82, post #17126605]

Quick 3‑step: how do I test/replace the audio path on GML 20?

  1. Inspect the amplifier module; reflow or replace the PCM1808 ADC.
  2. Power‑test; if speakers remain silent, replace TAS5706B.
  3. Verify headphone and speaker outputs, then burn‑in for several days. “Replace PCM1808 first; TAS5706B may also be needed.” [Elektroda, Kob82, post #17126605]

Do headphones work when the main speaker amp is bad?

They can, but very quietly. Users report headphone audio present at low level while the display shows volume changes. This indicates upstream audio conversion/control works partially, but output stages are compromised. [Elektroda, Kob82, post #16865258]

What is the TAS5706B in the GML 20?

It’s the SMD power amplifier IC (class‑D) driving the speakers. In documented cases, replacing it restored speaker output after front‑end repairs. Handle with proper thermal control during SMD rework. [Elektroda, Kob82, post #16872538]

What is the PCM1808 in the GML 20?

It’s an analog‑to‑digital converter (ADC) on the amplifier module. Multiple technicians advise checking or replacing it first when the unit powers up but audio is missing or low. [Elektroda, fellowes20, post #17109842]

What transformer spec should I seek for the GML 20 standby supply?

Use an approx. 3–5 W transformer with about 8–9 V secondary for standby. This matches observations from a teardown inquiry on the GML 20’s PSU section. Confirm pinout and mounting before substitution. [Elektroda, 398216 Usunięty, post #17126852]

My transformer reads short and blows the fuse—does that track with GML 20 failures?

Yes. A reported unit had a shorted transformer that heated rapidly and blew the fuse once disconnected from the board. Replace the faulty transformer, then re‑evaluate the downstream rectifier and regulators. [Elektroda, Kob82, post #17126605]

I don’t have electronics experience—where should I take my GML 20?

Use a radio/TV or car‑electronics service that handles SMD rework. Costs depend on diagnosis and shop rates. In‑person evaluation is required before quoting. [Elektroda, 398216 Usunięty, post #16866080]
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