Grundig TK23L audio problem
 

Hi, Im hoping someone has come across the following problem before, and save me hours of testing.
I was given a 1965 Grundig TK23 reel to reel, which was dead. After replacing some obviously faulty resistors, and a good clean up, it bust back into life.
Everything works as it should, except on playback, the volume is sometimes low, with quite a bit of hiss.
On tapping the connector junction from the playback head, it suddenly gets perfect. I have re-made the solder joints many times, all to no avail. its quiet, till a tap on the red lead from the head brings it back to life. I would like it working 100%, its a great old thing, and has a remarkably good tone.
Thank you in advance

Re: Grundig tk23l audio problem
 

Could be a cracked core in the lead itself, or the coupling capacitor into the first grid may be dodgy. Have you a diagram?

Re: Grundig tk23l audio problem
 

Hi, and thanks for your prompt reply. I do have a wiring diagram, but its for the tk 23 and seems slightly different. Mine is the later model, with a square, plastic casing. I was thinking of changing some capacitors, and this looks like a good place to start. I have seen suitable capacitors on ebay N.O.S , surely they will have degraded also? I have hundreds of capacitors, mostly radial, and nothing rated for 160 v. I guess im going to have to make a shopping list.

Re: Grundig tk23l audio problem
 

I got this image from a fellow user, I hope they dont mind. this is definitely the layout of my board. Unfortunatley, the resolution is not quite good enough to read any values.

Re: Grundig tk23l audio problem
 

Looks clear enough to me - I can read most values from your reduced image and you've also got the parts on the PCB which should have values marked on them. Don't worry about old NOS 160 volt caps - just use new 400 volt ones. They will probably be about the same size or smaller.

Re: Grundig TK23L audio problem
 

Thanks everyone for your help. I have now got the correct schematic and PCB layout. The problem is a bit strange, if I tap the connection with an insulated screwdriver, nothing. If it is not insulated, it makes a load pop and kicks back in, is it an earthing problem I wonder?

I really appreciate any advice given. This is the red wire, by the way, from the playback head. I don't think it carries any dangerous voltages.

Re: Grundig TK23L audio problem
 

I have attatched a better scan, some other user may find it useful.

Re: Grundig TK23L audio problem
 

You are shocking something into working
It could be a dirty valve base or the valve itself. (EF86?)

Re: Grundig TK23L audio problem
 

Thank you peter_sol. I guess thats my next port of call. I do seem to be going round in circles a bit. Could have bought a new one with the money I spent on replacement parts. But I guess thats not the point.
Thanks once again

Re: Grundig TK23L audio problem
 

I am looking at drawing number 7187-027. On the left side is the record play transfer contacts 1 to 24. The slider switch must work correctly.
The rotary track switch contacts direct which track is directed to c1 then to grid of EF86. (drawing E3

The manual is for TK14 TK/TS 19 TM 19 TK/TS 23.

The original manual is on my lap. 1963. So 55 years ago I repaired these machines. An overall joy is that now you have to do the same, and not I. :D

Re: Grundig TK23L audio problem
 

Don’t overlook the possibility of a broken PCB track, also.

Re: Grundig TK23L audio problem
 

Thank you everyone. The slide switch does appear to be ok, but it doesnt look to be user serviceable, I will change C1 and see if that helps, and also look very closely at the slider mechanism.
I have also checked the pcb tracks, and made good any that looked a bit iffy, but i will get my multi meter and double check, just to be sure.
Part of the problem is i have no stock of suitable components, I have everything needed to fix modern electronics, but they are always low voltage, and not suitable. I will continue and hope to post some good news shortly.
Thanks once again

Re: Grundig TK23L audio problem
 

Update. Today I went over all the pcb tracks with fresh solder, and re-made as many joints as I could. So far so good. It seems ok, with I believe more volume, Ill do a burn in test today, 3 hrs of The Black And White Minstrels will stress it for sure. It certainly stresses me :)
Thank you everyone for your advice.