Grundig TK144 - no sound

[Bobblybob]

Hi all.
For some bizarre reason I agreed to have a look at an old neighbours reel to reel m/c as the control switch had stuck in one position and a belt had broken. Complete newbie at this, however I have managed to replace all belts, made and replaced the felt pad that presses the tape to the head, made and replaced the rubber bush that had disappeared that was preventing the control switch from working properly and cleaned , greased and oiled throughout. Mechanically it now appears to work perfectly, however when I run a tape through it that I know has a recording on it... nothing. No sound. Even the level needle at the front doesn’t move. Any clues as to what (and how) I have to check to find out why?

It’s also the one model that I can’t find a manual for.
Thanks for help and advice in anticipation.

[paulsherwin]

Is the speaker completely silent (no hiss, crackling, humming etc)? If it is, *and* the level meter isn't moving, then it sounds as if no power is getting to the electronics. Check all internal fuses before doing anything else. It's also possible that you've dislodged a connector while doing mechanical servicing.

It goes without saying that you should clean all the switch contacts with contact cleaner like Servisol 10.

[Bobblybob]

Ok, thanks. I’ll check that first. I cleaned all the contacts I could find. I could only see one fuse though but I’ll take another look. No hiss or anything btw as you mention.

[ms660]

https://www.service-data.com/product...4/12367/m18754

Lawrence.

[DMcMahon]

Prettty sure that the VU level meter will only show the Record signal, although will stay illuminated during Playback.

Check the speaker is not turned off at the rotary tone control.

With the volume turned up quite high touch a finger onto the Playback/Record head wires, should hear a hum with Play selected if there is any life in the Playback amplifier.

David

[Bobblybob]

Thanks all. Downloaded manual. Wish I’d read about not removing 4 screws first..... hey ho, got it all back together ok. Regarding comment about touching finger on playback/record head wires, is that not dangerous? What’s the voltage there?

[Boulevardier]

Originally Posted by Bobblybob

Thanks all. Downloaded manual. Wish I’d read about not removing 4 screws first..... hey ho, got it all back together ok. Regarding comment about touching finger on playback/record head wires, is that not dangerous? What’s the voltage there?

No. Not at all dangerous. Zero voltage. Touching the playback head leads with your finger just introduces the electric fields that your body is picking up all the time from its surroundings, and you should hear this as a loud hum in the speaker - make sure it's switched to playback, and set the volume control fairly high. It's a good test for the amplifier, and used by engineers all the time.

Mike

[Bobblybob]

Will do, thanks. Anyway, update from tonight. Found that the 80mA fuse had blown. Replaced with one slightly higher as it was all I had. Lamp now lights up so that was obv the issue. 1 min later noticed smoke though rising from gap between casing and volume controls. Removed cct board as per manual (thanks). I can’t see anything major apart from a lot of what looks like brown varnish on some of the soldered joints and between tracks. I am guessing this could be issue? Recommendations how to safely remove? Thanks.

[Bobblybob]

Morning all.. Following on from yesterday then. I have traced the source of the smoke I think to resistor R38, which was getting very hot indeed. Anyone know whether this is simply a failing resistor, or whether there is an issue elsewhere causing this overheating? Nearly there hopefully and the old boy can get a surprise when I return it to him. Thanks as ever. Using multimeter it tests out at 2kohm, which I think it should be.

[DMcMahon]

Very difficult to know for sure, a good chance just failing due to age.

R38 is an HT voltage dropper so works somewhat harder than some of the other resistors, it drops the main HT at C21 down to a lower level at C15. These 2 electrolytic capacitors will be in a large metal can capacitor on the PCB. Check that the end (where the connections are) of this can capacitor is not swollen/breached open/leaking.

If you have a test meter check the output side of R38 (C15) down to ground to make sure there is not a low resistance. Leave at least 15 minutes after switching off to allow all capacitors to fully discharge before doing any measurements.

R38 is shown as 2.2kOhms 1/3 watt. Replace with 0.5W or even 1 watt would be OK, replacement may well be physically smaller than original.

After replacement if you can do it safely check the DC voltages as per the schematic, they all should be fairly similar values.

David

[DMcMahon]

If can be done quickly before smoke develops could be worthwhile measuring the voltage either side of R38 to see what the values are.

[DMcMahon]

These PCBs can be very messy looking due to loads of varnish, photo would be useful.

[Bobblybob]

Lots for me to do later. Thanks all for the advice. As soon as get some results from the tests I’ll let you know. Fabulous forum btw.....

[DMcMahon]

Difficult to tell from the photo but nothing obvious untoward with the PCB appearance.

David

[paulsherwin]

If things are smoking then something is seriously wrong though. Look for any short circuits that have been inadvertently introduced.

[martin.m]

I have repaired several of the very similar TK120s and find the usual reason for this resistor overheating is leakage in the smoothing can. It can be replaced with two seperate 47uF 350v capacitors if necessary.

[Bobblybob]

Attachment 227909#Martin. Which capacitor from the attached?

[DMcMahon]

It's the C21/C15 referred to before, bottom left corner.

[Bobblybob]

Will do, job for the morning. Thanks all. More updates to follow.

[DMcMahon]

Originally Posted by DMcMahon

Its the C21/C15 referred to before, bottom left corner.

I should have said bottom left corner of Printed Circuit Panel (component layout) drawing.

David