Grundig TK141 very low sound

[Sideband]

In post 11 you seem to have two circuits....one of which is for a radio!! Make sure you are only using the TK141 circuit or none of it will make sense!

[jimboradio1]

So the voltages on the sheet checked mostly close or spot on Is there a percentage they should be in?.

Refreshed my memory on Transistors as a previous member suggested ( Seems to have removed his post for some reason),And will start looking at those next.

I'm sure an experienced electronic fault finder would know where to start and the most suspect components to look at But I am enjoying the challenge,If I didn't have the circuit diagram I don't think I would attempt it.

This was a free item in good condition and doesn't warrant the cost of a professional repair,So I'd rather have a go rather than scrap it, Nothing to lose.

Thankyou for all the advice offered so far

[jimboradio1]

Originally Posted by Sideband

In post 11 you seem to have two circuits....one of which is for a radio!! Make sure you are only using the TK141 circuit or none of it will make sense!

Thank you I had discovered that and thought nobody had noticed haha

[Welsh Anorak]

The track switches can cause trouble on these. Engage 'play' and there should be a noticeable hum from the speaker, which should change or crackle as you play with the track buttons. If not then it's the amplifier which i admit isn't too easy to access. You have fairly conventional transistor amplifiers. A signal generator is helpful here - this can be a wet finger as it's a solid state circuit! I'd work back from the volume control as it's easily accessible to ascertain if the fault's north or south of this.
Ideally you'd be using an AF generator and 'scope, but I'm sure you can get this going with a little ingenuity!

[jimboradio1]

So got myself one of those cheap signal tracer injecters and still not sure what to do with it?

[ms660]

Have you tried playing back a known good recording?

Lawrence.

[jimboradio1]

Yes done that, Can hear the track faintly running through the heads but nothing out of the speaker.

[ms660]

Does the record level meter indicate ok when recording and can you hear the signal ok in the loudspeaker when recording?

(Just trying to establish what is and what isn't)

Lawrence.

[jimboradio1]

Don't have a mic Lawrence but when record is engaged audible sound comes through the speaker and is controllable with all three sliders, level meter moves when touching the track selector board contacts.

[ms660]

It sounds like the amplifier stages are working from what you're reporting, if so then it points to switches, head/head to tape contact.

If the switches and head have been cleaned (which they should have) It might be worth double checking the signal path around the head track switching, in playback mode with tracks 1&2 selected (the upper head segment) inject a signal at track switch contact a2, a2 is the signal output from the upper head segment, it's shown on the track switch board layout and also on the schematic, the signal output from the loudspeaker should be ok if all's well, next inject a signal at track switch contact b2, b2 is the ground for the same head segment, there should very little or no output from the loudspeaker when injecting at that contact if all's well.

You can check the other track switch contacts using the same procedure except that tracks 3&4 (the lower head segment) are selected and the signal is injected at contacts g2 and h2 respectively.

Lawrence.

[jimboradio1]

Thanks for that Lawrence, If I'm doing things correctly then yes I get a tone at A2 and next to nothing on B2, not exactly the same on 3 and 4.

I lost the sound completely at one point and found that that the slider mechanism used for recording was coming all the way home, So when helped along it came back but still very low sound coming from speaker. Will investigate that a little more tomorrow.

Starting to think you may be right and could be a switch fault.

[ms660]

I don't know whether the switch contacts are faulty or not but the tests given should be able to guide you as to whether they are making contact or not if the amplifier's working, I didn't include the D position but if you want to check the contacts in that position inject a signal at contact a2 as before, you should get an output, then inject the signal at contact h2, injecting at that contact should give no or very little output.

The D position connects both head track segments in series so that two tracks can be played back through the amplifier at the same time.

In the other track positions one head track segment is connected to the amplifier and the other is connected to a monitor socket that a separate monitor amplifier can be connected to.

Lawrence.

[jimboradio1]

SUCCESS!!,Lawrence you were correct it turned out to be the selector play switch that had eluded me as I assumed that was purely mechanical shifting the tape and didn't realise it also made and broke contacts.

A logical and systematic approach would have revealed it earlier, Instead I dived into the electronics,I had Five different transistors out for testing haha.

Not all bad I have learned a lot from this project and have enjoyed the challenge + a bonus working machine.

Thankyou to all who have given help and advice and tolerated my inexperienced ramblins I am very grateful.
Also you help and support have saved another machine from the tip .

Regards Jim

[Welsh Anorak]

Well done - and that's something to add to the faults you can encounter on these!