Grundig V5000.Noise in the left channel.

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José_Ramón_Ameijeiras_F...
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#1 erstellt: 17. Okt 2013, 01:15

I have a Grundig V5000 amplifier with occasional noise in the left channel .
The noise appears in all situations and without any attached peripherals, and with the volume to zero.
No change to acting on any control .
After applying contact cleaner spray everything is equal .
I have checked all contacts , connections, switches and condition of welds .
As seems casual contact , I have applied a spray of cold and hot air
to check a break invisible copper track .
I have also made pressure in different zones of the circuit to check a
poor contact .
Measured voltage values corresponding to the original scheme.
There are not electronic component broken , burned or warped.
All welds are apparently correct.
I cleaned the contacts of the output relays speaker .
The speakers are new.
Perfect operation when no noise.
I ask the help of an expert in this type of equipment.
Thank you very much .
Greetings from Madrid ( Spain ) .
J.Ramón.

Steffen_Bühler
Inventar

#2 erstellt: 17. Okt 2013, 10:29

This seems to be a problem in the input stage. Replacing the preamplifier transistors with low noise types often helps immediately. Furthermore, Grundig loved those tantalum capacitors in the signal path. These tend to add noise when aged. So think about replacing them as well.

Best regards
Steffen

fmmech_24
Stammgast

#3 erstellt: 17. Okt 2013, 18:00

repair-manual in german

bukongahelas
Inventar

#4 erstellt: 17. Okt 2013, 18:58

Connect Amp only to AC Power and use Headphone.
Turn MasterVolume to min.
Solder two wires across NF Audio Inputs and Signal-GND of Power Amps.
Shorten audio inputs of power amp(s).
Now definite no signal comes into power amps.

If noise is still apparent , error is in (one) power amp.
More in the difference amp or bias-section than in the driver and last powerstage.
If double/triple diodes are used for temperature compensation , they often tend to generate noise.
Use 2or3 normal diodes in series as spare (isolated in heat shrink hose).

If silence then preamp is failure source.
Change (across channels) small signal transistors or replace them all.
Nice spare type is 2SC2240 , Pinout is "japse" compatible , ECB , read from left to right, legs down and
characters showing to your face.
Replace tantalum caps if built in for mylar types.
Series WIMA MKS-2 is nice , quite large capacity , 50/63 Volts and not so big.
For spare elkos i use Panasonic FC 105° .

bukongahelas