Grundig 3028 HELP - diyAudio
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Old 11th December 2010, 08:53 PM   #1
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Default Grundig 3028 HELP

My second re-cap job

I just finshed re-capping my Grundig 3028 and now I have no volume control, just one steady volume, tone is flat also

Does anyone have pictures of the under chassis with nice close ups of the capacitors so I could compare? That would help alot

I am a novice and not too good at using the schematic to trace the signal path

I did put an ohm meter on the volume pot and it does show change so I am pretty sure the pot is fine

This radio played ok except for a hum

I replaced 15+ capacitors, everything I could think of or was suspect

The pictures I took of the original caps were blurry and I have no nice reference (BIG MISTAKE)

Maybe some idea of where to start
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File Type: jpg smaller.jpg (511.0 KB, 107 views)
File Type: jpg schematic_2048.jpg (477.3 KB, 105 views)

Last edited by Omegaman; 11th December 2010 at 09:11 PM. Reason: spelling
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Old 11th December 2010, 10:04 PM   #2
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Check that you haven't broken the 'earthy' end connnection of R31 (390 Ohm), or the other end of R31 which is tied to the low-volume end of the volume control pot.
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Old 11th December 2010, 10:50 PM   #3
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I checked R31 and the low-vol end of the vol pot is connected to R31 and the other end of R31 is connected to GND

From the GND side of R31 to the low-vol pot, I measure 386.5 ohms which is R31
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Old 12th December 2010, 06:27 PM   #4
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Well you do have a schematic - which is more than many fixers of vintage stuff have, so it isn't going to be too difficult to trace out the audio pre-amp section. It's not very big.

Is the fixed volume low, medium or loud?
And is the tone normal, or poor bass, poor treble?
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Old 12th December 2010, 07:10 PM   #5
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Default Newbie hubris

Steerpike, thank you for assisting me in this problem.

It turns out I had incorrectly connected C47. (see photos) Once I matched the schematic with "as built" then the volume was restored

This was a great lesson in tracing circuitry using the schematic.

LESSON: ALWAYS TAKE LOTS OF PICTURES AND CLOSE UPS

The tone controls do function but there is a tinny sound to the signal. I will continue reviewing the changes I made

Its all good
Attached Images
File Type: jpg C47.jpg (187.5 KB, 78 views)
File Type: jpg C47 schematic.jpg (113.9 KB, 73 views)

Last edited by Omegaman; 12th December 2010 at 07:14 PM. Reason: adding detail
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Old 18th December 2010, 05:18 PM   #6
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Default I found the problem

I found and fixed the tinney tone problem and now the Grundig 3028 is restored to its full glorious Hi-Fi sound

Yes, I connected a capacitor wrong

The .15uf 125v capacitor C58 was not connected to the output from the second coil in the circuit

no harm done

Excellent opportunity for me to follow schematics and trace circuits

LESSON: PICTURES< PICTURES< PICTURES

I also added small connectors to the speaker outputs in order to pull the chassis faster without soldering/desoldering each time I had the chassis out

Now a new 3 prong power cord

The radio is now worth the expense of purchasing a new EM34, or perhaps one of the alternate tubes

Now its back to my 59' Blaupunkt to solve that balance control issue, then rebuild the Fisher FM-100 and recap the X-100, then I can start the recap of my VOM 869 Amp, preamp, tuner and R2R tape deck. followed by the VOM 1428 amp and 1416 tuner. Then the twin heathkit EA-3 amps and then start on the Wharfedale W70-E's and recone the Bose 301's and I'm done

Thanks DIYAUDIO
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Old 18th December 2010, 10:41 PM   #7
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Those German sets are magnificent. Yours must be an export set since the German market ones only went to 100MC/s on FM.

EM34s can be disgustingly expensive, but they do look so good when you have a bright new one in!
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Old 28th December 2010, 06:57 PM   #8
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Default EM34 replaced by 6E5C magic eye

Since this Grundig 3028 restore is function first, I decided to forego the $50-$100 EM34 and instead go with an alternative solution

I got a 6E5C and did the simple wire mods to use the 6E5C instead of the expensive EM34.

The eye works great.

I placed a notice on the chassis indicating the 6E5C mods for the future generations a-coming

The NOS 6E5C cost $20 with instructions
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