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Old 31st May 2019, 5:26 pm   #1
Salvatore79
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Default Grundig Hit Boy 310 no sound, hum from the speaker

Hi all friends, I am a new member but I have been following your forum for a long time, a great forum compliments and I hope you can help me identify the problem on my radio, thanks to all of you in advance

As written above the radio in question Grundig hit boy 310 does not emit any sound even if part of the amplifier seems ok. I have changed some electrolytics of poor capacity but they have not solved. Turning it on by knob that is also the volume, when you hear it bump on the speaker and then stop only a small buzz that varies at the same value of the volume, clean even the deviator am / fm but nothing, touching some components with the fingers the hum tends to increase, I know they are inter-interferences. I thought of some cold welding but I have done almost all but still no modulation and audio mute, I hope you can give me a straight for repair, I forgot I have two radio hit boy 310 on the same state, I think they have the same problem both, thanks to all those who will join.

Last edited by AC/HL; 31st May 2019 at 6:05 pm. Reason: Forum rules
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Old 31st May 2019, 6:08 pm   #2
AC/HL
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Hello and welcome Salvatore.
We are unable to post schematics from Radiomuseum, but members who don't have a copy can download it themselves.
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Old 31st May 2019, 6:51 pm   #3
Salvatore79
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

I apologize I had not noticed the pdf radiomuseum
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Old 31st May 2019, 9:58 pm   #4
cathoderay57
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Hi Salvatore, I also have a Grundig Hit Boy 310. The transistor numbers refer to the Grundig circuit diagram that you can download from the RadioMuseum. To make mine work I had to replace T103 the AM mixer-oscillator transistor which is type 2SC1417 and to work on FM I replaced T102 in the FM part (2nd stage), also type 2SC1417. You can get these transistors on eBay, they are not expensive. Hope that helps, good luck, Jerry
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Old 1st Jun 2019, 2:57 pm   #5
Salvatore79
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Thanks Jerry

I will look for the position of the components you suggested and I will replace them, I don't know if your T102 and T103 positions are silk-screened but your position on both radios is not written on mine, however it will not be a problem to identify them, thank you update short
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Old 1st Jun 2019, 8:41 pm   #6
Salvatore79
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Replaced T102 and T103 with BF241 as per datasheet but the result does not change, some other idea .. thanks
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Old 2nd Jun 2019, 8:54 am   #7
cathoderay57
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Hi Salvatore, if you are getting a buzz from the speaker when you touch the volume control slider connection it sounds like the audio amplifier is working. I would check any electrolytic capacitors in the AF area particularly C701. Then it is necessary to measure the voltages on each transistor and compare with the values quoted in the service data. If you find a big variation then either the transistor is bad or a component nearby has changed value and is affecting the biasing. Cheers, Jerry
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Old 2nd Jun 2019, 8:49 pm   #8
rojosuiza
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Do you read a signal at MP3?
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Old 3rd Jun 2019, 10:01 pm   #9
tri-comp
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Google + grundig hitboy 310 =

https://www.vintageshifi.com/reperto...ice-Manual.pdf

Now the service-manual is available for anybody who cares to download it.

Good luck with repairs.

Rgds,

/Torben

Edit:
That didn't work so well, copying the link into the forum-post.
Don't quite know why, as the link works fine when selecting it from Google.
I'll just attach the (compressed, because of forum-limits) file instead.
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File Type: pdf Hit Boy 310_.pdf (724.9 KB, 107 views)

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Old 4th Jun 2019, 2:52 pm   #10
Salvatore79
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Thank you all for your cooperation

Jerry thanks, I assume too that the amplifier is working and that the problem is before the amplifier, I replaced all the electrolytics on the circuit except those of power supply, replaced also C701 by 1uf still without result, I have already started with the measurements on individual transistors, I hope to find the culprit, thank you very much

Rojosuiza it would be an interesting test to exclude the amplification part, could you tell me where to inject the signal? thank you all

I apologize if some talk is incomprehensible, I write from Italy and I use google translate which sometimes does not translate as it should ..
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Old 4th Jun 2019, 5:03 pm   #11
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

The slider of the volume control would be a good place to inject an audio signal.

Before doing that though I'd check that there's 6 VDC across C719 and C709.
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Old 4th Jun 2019, 8:13 pm   #12
rojosuiza
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Connect radio to a small external amplifier and try to find if you can find a signal at switch S1 2i/2j/2l.

Also you should be able to hear a signal in the hit boy amplifier, if you inject it at the switch S1 2k.
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Old 15th Sep 2019, 10:05 am   #13
mkultra
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Default Re: Grundig Hit Boy 310 no sound, hum from the speaker

Hello from a newbie
found here via the big search engine... see another post

one thing i noticed about the hit boy 310 - mine seemed dead at first try aswell. it doesnt make fm noise for some reason. you only get sound if you have tuned a fm station, otherwise it remains astonishing silent, very unlike the other fm receivers i know. even on full volume the "hiss" is barely noticeable.

i dont know if this is intended (controlled by signal strength?) or a "hidden feature" but its really nice for that little radio. i see it as feature
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