Korg tape echo issue

[andre tchmil]

I’m having a korg tape echo with low echo output. I have a perfect 50khz on the erase head but what voltages should I have on erase and record head?
could it be that the oscillator puts out a too weak signal ?

 

[abbey road d enfer]

It's quite difficult to answer because it depends very much on the choices made by the designer regarding the head inductance.
Typically on this type of machine the erase voltage is 10-50V, and the bias voltage on the record head is 2-20V.
You don't have a schemo?
I suppose you know you have to clean and demag the heads regularly...

 

[andre tchmil]

it's a SE300. I have the schematic of a SE500 but I guess the circuit should be more or less the same.
I don't see any values printed on it.

 

[abbey road d enfer]

Sometimes, with just the schematic and the power rail values, it's enough to get an idea...

 

[andre tchmil]

measured the transformer : primary 4r, center tap 2r. Secondary 2r, side that goes to 4700PF is 0,1R. I'm also measuring there less than 1V. Comparing with the Roland space echo , it should give 45V. Is my analysis correct ?

 

[andre tchmil]

 

[radardoug]

Side that goes to the 4700 pF is .1 ohms? Thats a short. Check both caps. Do you have a scope? Use it to check the primary side is oscillating. If necessary remove the 4700pF and see if its working. Apply simple fault finding logic.

 

[andre tchmil]

Side that goes to the 4700 pF is .1 ohms? Thats a short. Check both caps. Do you have a scope? Use it to check the primary side is oscillating. If necessary remove the 4700pF and see if its working. Apply simple fault finding logic.

yes , did all the above things. Removed the trafo from the board, it's a short. I'm trying to peel it open now .

 

[abbey road d enfer]

Side that goes to the 4700 pF is .1 ohms? Thats a short.

+1

 

[andre tchmil]

I opened up the small can, but instead of trying to repair I would opt for a small replacement stepup transformer.
I figured out that Roland has 45 volt at the erase head, I have 12V at the primary, so a 1:4 would do.
Any suggestions for it in the 50Khz range ?

 

[abbey road d enfer]

Actually you should have about 20Vrms across the whole primary
I very much doubt you can find a drop-in replacement. You need to have the same inductance, not only the correct ratio.
You may find an out-of-order SE500. Rewinding the xfmr should not be too difficult; there are no particular constraints here, only patience is needed.

 

[andre tchmil]

was thinking to rewind it. It has only 60 and 21 turns