can you help me repair the amp in an electric piano please?

[Henry Kolesnik]

The voltage on TR11 and IC1 seem to be closed enough but TR13 is too far
off. Check to see if TR13 is shorted or some of the components around it
are bad. Are the collectors fuses good?
hank wd5jfr

 

[Salvatore]

Hello

I would like to fix the amp in an Wurlitzer 200A electric piano. The
schematic of the amp is here;

http://mitglied.lycos.de/domonack/Wurly200Aschemo.jpg

Symptoms are; No sound comes out of the built in speakers. When I
connect an external amp I get very faint sound/crackle/noise with the
volume turned up full. (the level potmeter next to the aux output
which is adjusted by a screwdriver is turned to max).
I've done some measurements;

1) At the point in the schematic marked with a 3 with a square around
it, there is signal. When I connect this point to an external amp I
get sound. But at the point marked 13 with a square around it, I don't
find signal.

2) Emitter of TR11 has 23,6 Volt

3) Emitter of TR13 has 7,65 Volt (which is WRONG!)

4) IC1 pin3 has 14,28 Volt

I you could tell me what test I need to do to get closer to fixing it
I will do them.
I appreciate your help - thank you!

Marty

 

[**THE-RFI-EMI-GUY**]

Schematically, something is wrong. I think -22.5 VDC from D3 and D5
(rectifiers) should be present on emitter of TR13. Is TR8 collector tied
to TR13 emitter? I think it should be. If so I would conclude the -22.5
supply is one of the problems. Your symptom at test point 13 has me stumped.

Let us know what you find.

 

[Mark]

Schematically, something is wrong. I think -22.5 VDC from D3 and D5
(rectifiers) should be present on emitter of TR13. Is TR8 collector tied
to TR13 emitter? I think it should be. If so I would conclude the -22.5
supply is one of the problems. Your symptom at test point 13 has me stumped.

Let us know what you find.

Used to work on these things. Not the most pleasant piece
to troubleshoot. Be aware that there were numerous
variations of this assembly. Don't know if you've got the
right schem for yours or not. Be careful of the tine rail.
It's at a positive voltage (NOT ground).Defective trim pot (203717-1) or crushed (shorted) cable
going to front panel volume control.Check ALL your voltages against what's shown on the schem.
--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.

 

[James Sweet]

The piano was recently shipped with FedEx from USA to Norway and I
think it has taken quite a beating.

Wow, that couldn't have been cheap!

 

[Ralph Wade Phillips]

Howdy!

... One should think FedEx loads the packages into
a big cannon and fires them off into a brick wall before handing them
over to recipients.

Naw, they just drop ship them from 20,000 feet.

RwP

 

[Mark]

Thanks to you who have helped me. I have now found and solved the
problem. I screwed off the PCB to look closer at parts and then
noticed a 5 cm long crack in the PCB. The crack was barely visible
from above, but several of the tracks were broken. I made good the
connections and now the amplifier plays like it should. There is some
crackle from one of the speakers. It doesen't sound like it's blown,
more like if the cone is rubbing against something or there is a loose
object in there. I will take it off and see.

Glad you found what turned out to be a simple repair. As to
the speaker, those old paper cone speakers are likely to
have developed tears, especially at the surround. A light
application of silicone will usually take care of it.
--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.

 

[Salvatore]

Used to work on these things. Not the most pleasant piece
to troubleshoot. Be aware that there were numerous
variations of this assembly. Don't know if you've got the
right schem for yours or not. Be careful of the tine rail.
It's at a positive voltage (NOT ground).
Defective trim pot (203717-1) or crushed (shorted) cable
going to front panel volume control.
Check ALL your voltages against what's shown on the schem.

Hello again

Thanks to you who have helped me. I have now found and solved the
problem. I screwed off the PCB to look closer at parts and then
noticed a 5 cm long crack in the PCB. The crack was barely visible
from above, but several of the tracks were broken. I made good the
connections and now the amplifier plays like it should. There is some
crackle from one of the speakers. It doesen't sound like it's blown,
more like if the cone is rubbing against something or there is a loose
object in there. I will take it off and see.
The piano was recently shipped with FedEx from USA to Norway and I
think it has taken quite a beating. It was inside the original wooden
trunk (tolex covered) and the sides of this was more or less ripped
off the top and bottom. The metal locks was twisted and bent out of
shape sideways. I was happy the piano itself looked OK, and I'm moreso
now seeing that all the mechanics inside the piano is OK considering
what it's been through. One should think FedEx loads the packages into
a big cannon and fires them off into a brick wall before handing them
over to recipients.
Anyway, a big thanks to you who helped me. I saved the money I would
have spent on a workshop, and I have the satisfaction of having found
and fixed the problem with my own hands.

regards,
Marty