Kawai KDP 80 Electronic Piano Dead

[pavb2]

Hi all

Glad to join the community. I have a Kawai KDP 80 Electronic Piano and can't get anything out of it. I've traced the 230 volt supply through the board and have 230 volts at the primary side of the transformer a Bando KT-031. The problem is I don't know what the secondary supply from the transformer should be and can't get any information I've tried Kawai and their distributors etc. The secondary is the two blue wires on the right of the picture.

I've got the service manual attached

but can't see what the secondary is any help appreciated.

 

[Nigel Goodwin]

What voltage do you have on the two blue wires from the transformer, if it's 'anything' the transformer is OK, if it's nothing the transformer is faulty.

The actual voltage is simple to guesstimate (as you've attached the service manual), it feeds through a bridge rectifier to a 25V rated reservoir capacitor - so the DC out has to be less than 25V. From there it feeds a power output IC, which wants about 18V DC, and also feeds an active smoother (Q12/Q13) which has a 16V output, so requires a similar 18V or so input.

So the AC output from the transformer needs to be about 12V RMS, or a little more.

 

[pavb2]

Thanks Nigel I have 230 at the primary but nothing coming out of the two blue secondary wires a like for like transformer is no longer in stock.

In looking at the block diagram page 15 I thought the secondary voltage might be 20 volts but didn’t want to guess and potentially blow the pcb’s also what Kva rating is the transformer

 

[Nigel Goodwin]

Thanks Nigel I have 230 at the primary but nothing coming out of the two blue secondary wires a like for like transformer is no longer in stock.

In looking at the block diagram page 15 I thought the secondary voltage might be 20 volts but didn’t want to guess and potentially blow the pcb’s also what Kva rating is the transformer

20 volts would be too high, it would give about 30V on the 25V reservoir capacitor - BOOM!!!.

As for the power of the transformer, you can estimate that from it's size and weight, both of which are pretty representative of the power - it's doesn't matter if it's higher power, just not lower.

 

[pavb2]

Thanks again Nigel what transformer would you recommend I’m in UK so could get one from R/S Components?

 

[Nigel Goodwin]

Thanks again Nigel what transformer would you recommend I’m in UK so could get one from R/S Components?

What does it weigh, and what are it's dimensions?.

This one is 20VA and weighs 550g

RS PRO 20VA 2 Output Chassis Mounting Transformer, 12V ac, IEC 61558-2-6 | RS

uk.rs-online.com

 

[alec_t]

A chunky old-school transformer like you have is unlikely to fail unless something downstream draws excessive current. Have you ruled out all other posssible failure points? It would be a shame if a replacement transformer suffered the same fate.

 

[rjenkinsgb]

The manual you link is apparently not quite correct for your keyboard - the PSU board in yours is labelled "KEP-389" and has a lot! more components on it than the KEP-348 schematic in the manual, including optoisolators and transistors etc.

I wonder if there are other differences at the secondary side of the transformer?

Where do the black & white wires, and the yellow wires, from the AC board go to?