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grundig: Grundig TK64 Restoration - Blowing HT Fuse.

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » grundig: Grundig TK64 Restoration - Blowing HT Fuse.
           
David Roe
 
 
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14.Nov.18 12:28

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Hello to everybody from Sydney,

I am restoring a Grundig TK64 and if there are experts please comment. 

1) it is blowing the 250mA fuse

2) I disconnected the B+ at the Rectifier, and measured the voltage at the DC output of the Rectifier.  OK ! about 220v and the fuse is not blowing.

3)  I disconnected the Power amp, which has a single connector.  fuse still blowing.

4) I replaced the main 50uF + 50uF filter capacity with a new unit, fuse still blowing

 

What is the big red capacitor (?)  with a large bolt to mount it to the chassis ?  

 

Should i remove ALL valves and test again ?   I dont think valves will cause a high current short...??

There are many wax capacitors in the unit ?

There is also a 2nd 50uF + 50uF filter capacitor which i have not replaced.

 

Any suggestions on what i should try next ?  maybe change the 50uF + 50uF capacitor ? 

Thank You.

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Rolf Beckers
Rolf Beckers
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14.Nov.18 15:46

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Dear David,

I see three 50 uf capacitors C 16, 17 and 18. Each one of the could be the reason for the problem.

I don't know which one you have changed. You have to check them all. Just disconnect them and see if the fuse still blows. Check also that the fuse has the right rating 250mA and slow!

Regards

David Roe
 
 
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17.Nov.18 08:42

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Good Morning,

I took a while, but i have replaced the 4 main 50uF capacitors.   (2x in each can)

I believe in the schematic they are C4, C16, C17 and C18.

After replacing these two capacitors the fuse did not blow, the volatage was 290v, but came down to 220v after keeping power on for some time.  

I pressed play and turned the volume up and  can hear slight crackling from the speakers, then later a little hum at full volume.  !  this is very good...   I am waiting for drive belt from germany so cant test fully.

PROBLEM.

I connected a mic, and pushed the button on the left, says R/S in red, the EM84 was working and my audio was making the EM84 move,  very happy !!

But after 2 minutes,  the mains fues blew again, so there are more faulty capacitors.

I disconnected the power amp, and the fuse is still blowing,  seems to some capacitors related to the record function of the schematic.

I dont have time to just replace all of the caps, so if any expert can give me suggestions, i will start there..

Thank you

David 

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David Roe
 
 
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17.Nov.18 12:32

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Its bee a busy Saturday afternoon, and i was determined to find the new problem, after replacing the main filter capacitors.  
 

1st Problem.  The main filter caps were drawing too much current and blowing the V+ fuse.  After replacing the main filter caps it did work for about an hour.  When i tried to record, it started blowing fuses again.

 

2nd Problem.  After disconnecting the power amp, cutting one lead of almost every wax capacitor, and removing every valve, it was still blowing fuse.

 

i discusonnected the +ve from the bridge rectifier and it was STILL Blowing a fuse, so finally i disconnected the bridge rectifer and measured the transformer AC voltage to the bridge rectifier and it was good !  no blown fuse.  The problem is a shorted bridge rectifier.

I opened up the bridge rectifier and you can see something has melted inside between the wafers..

Hoping to replace most of the wax capacitors tomorrow and put in a new IN4009 bridge circuit with a reducing resistor. 

Any suggestions on what value and wattage resistor to reduce the V+ ??

 

 

 

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David Roe
 
 
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18.Nov.18 12:55

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Good Afternoon.

 

Sunday night here, i am delighted to advise the old Grundig is almost fully restored.

This afternoon, i replaced 80% of the wax capacitors,  some small ones i could not reach.  

I built a new bridge rectifier using IN5408, what are 3A, 1000V diodes.

I added a 100ohm, 10W resistor but maybe dont need it...

I tested the following to get the output voltage close to spec.

 

DC after rectifier = 290V

DC after 100ohm resistor = 278

Voltage drop across 100ohm resistor 10v,  so its dissippating 100mA or 1W.  Well within the 10W

After runnning for some time, the output was around 277v, so very close to spec.

 

please see my youtube video.

 

I am waiting for a drive belt for the main reel  from ebay germany, taking a long time.  I tried turning the take up spool by hand, and the sound was clear !!  the Magic eye works very well as well. 

Cant wait until my drive belt arrives !!  

 

 

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This article was edited 18.Nov.18 14:21 by David Roe .

David Roe
 
 
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19.Nov.18 12:55

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I have completed the restoration.

The unit records and plays beautifuilly, and the sound is loud and clear.

Please click this link to see my restoration =>  video's  if you have a similiar unit. 

 

This article was edited 22.Nov.18 18:42 by David Roe .

David Roe
 
 
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23.Nov.18 15:27

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I REALLY NEED HELP, HOPING SOME EXPERTS ARE HERE 

I have brought power back up, record and playback working well, BUT

I let it play for 2 hours, and it was getting hot, i could feel the heat.

THEN THE MOTOR JUST STOPPED 

All the Relays are working and clicking as normal,  the HT is working and the magic eye is working, evertyhing seems ok, BUT THE MOTOR WILL NOT SPIN !

I have measured the voltages across the motor, PLEASE SEE PHOTOS.

BUT THE GRUNDIG TK64 is only getting

0AC

127AC

133AC

 

I tested a Grundig TK40, and measuring across the 3 pints, i got

119AC

315AC

285AC

 

I DO NOT KNOW WHAT THE PROBLEM IS !!    Its almost impossible to replace the starting caps, as they are between the chassis and the electronics.  ALSO, there are two large capacitors between the Chasssis and the electronics, impossible to see the wiring to them.  

 

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David Roe
 
 
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24.Nov.18 09:42

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The schematic and motor connections dont see to match my TK64.

I fix the problem.  I had to split the chassis

In the middle there is a 4.3uF and 2uF motor run capacitor.  The 4.3uF was open circuit

The Motor says for 50hz it needs a 6.3uF.  So i added my new 5uF + original 2uF,  and got a measured 6.6uF.

The motor is working well and it records and plays in MONO.

Unfortunately STERRO is not working, as the head has one open coil. 

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This article was edited 12.Dec.18 14:38 by David Roe .

David Roe
 
 
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29.Dec.18 11:49

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Good Morning,

 

Until i get a new head, i use it in Mono for recording / playback.

The amplifier works in Stereo very well.

Please see my video of the latest test.

  
rmXorg