Dynacord Echocord Mini, no echo!

[thijsdrum]

A while ago I got a Dynacord Echocord Mini. To start of I cleaned the whole machine and heads. I got new tapes from MyTapeEcho. So the mechanical part works very good now.

After testing the echo did not work. So there is guitarsignal comming trough but no echo. I replaced a bad resistor in the amp in front of the record head which got the signal further. Still there is no echo.

If I desolder the record head I get this signal at connection 16 of PCB B3001 (schematics, see below)

https://www.youtube.com/watch?v=SX26Ov91riU

As you see it does react to the guitar signal.

When I solder the record head back on I get this signal. (see attachments) It does not react to the guitarsignal.

So the bias sine seems to work and the head measures about 90ohm.
You can find the schematics here: http://www.synfo.nl/servicemanuals/D...SCHEMATICS.jpg

Is there anyone with the same machine? Or does anyone know wat is wrong here?

Thanks in advance!

 

[JonSnell Electronic]

I presume the signal you measured is on the record head. Have you got 1mV on the playback head? If not, may sound silly but I had a WEM copycat for repair and the tape was inside out. The splicing tape was on the head surface side!

 

[thijsdrum]

Thanks for the reply!

Today I put a small sine directly on the record head and I could hear it being played back. So now we know that the record head, playback head, erase head and tape are good.
Still I have no idea what could be wrong with the record section.

 

[JonSnell Electronic]

Don't jump in too deep.
Follow the signal path. I find it easier to go backwards, (it's my thing). What have you got on T12 collector, see the boxes with marked values. Go backwards if no signal. You will soon find the error.

 

[thijsdrum]

With the full circuit connected I get this on the oscilloscope for the collector of T12:
View attachment F0000TEK.BMP

For this measurement I put a 1kHz signal on the input.

 

[JonSnell Electronic]

So, the question is; why is in not getting to the tape?
Firstly, check on the record head for that signal with bias on it. then if there, what is on the grounded side of the winding in the head. Should be nothing.

 

[JonSnell Electronic]

Don't forget to look at the oblong voltage boxes!

 

[thijsdrum]

The voltages seem good. I made another video of the scope. This time at connection 16 of PCB B3001 with the whole circuit connected. As you can see the signal does react to the 1kHz if I crank up the volume.

https://www.youtube.com/watch?v=DYMnM5izXWM
Does this help?

Extra info: I replaced C105, C106 and R306 before the first post here. Also nothing measured at the ground of the record head.

 

[thijsdrum]

I managed to fix the echo. Turned out it was a bad transistor after the playback head...

But now the echo sounds bad. The clean signal is still ok.
The next video will let you hear what I mean. I did lots of measurements but I can't seem to find any bad components. Any ideas? Tape turning to slow?

https://www.youtube.com/watch?v=1dAWkOFsLEw

 

[dotneck335]

Scope on the record head should show audio signal mixed with bias (100+kHz) voltage.

 

[thijsdrum]

Hi dotneck335, in post #8 I posted a video that shows the measurement on the record head. So there it shows about 60kHz. Would that be enough?

 

[norpal]

Dynacord echocord mini , Maestro echoplex 3

I am living in Virginia USA looking for a good tech. to repair my Dynacord Echocord mini and Maestro Echoplex3 , can somebody knows some good tech in USA?
Thank you in advance for your help