Vintage Synth Repair

Keith and Group,
Keith, I tried emailing you off-list a couple times but got no 
reply. Probably the victim of a spam filter somewhere. Anyhow, I 
found the problem and thought I might share it here for future 
use....

As you might recall, I had a problem with my Wurlitzer 4520 Theater 
organ. The Melodia voice was dead from C#(key #38) on upwards and 
also the Chimes weren't sounding properly. On some of the chimes, 
only one or two of the three or four required notes for each chime 
would sound. A Wurlitzer technician, Mark Morelock, suggested I 
check the coupling capacitors on the lower manual keying box. Well, 
those checked out fine. After looking at the schematic (#653543), I 
noticed that the Melodia notes above key #38 came from the flute 
signal which was split into 5 sections in the lower STRAF boards. 
Using an oscilloscope and holding down the affected C# keys with 
only the Melodia voice "On" to provide a signal to track, I traced 
the signal from the lower keying unit outputs to the Flute Preamp 
and Phase Inverter (TR3) on the Lower STRAF unit. I found that the 
voltage on the collector of TR3 was high; 11.7 VDC instead of the 
9.7volts. Also found that I lost the Melodia signal between this 
point and the Complex Signal Preamp (TR2). The 2mfd capacitor at the 
collector of TR3 was the culprit. It had gone open. After replacing 
it, The Melodia and Chimes now all sound properly!! So if anybody 
reading this has a similar problem with a 4500 or even the 4300 
series organs (they share these same circuits), giv a look at the 
circuits mentioned. Might save ya bunches of time elsewhere!

Rich in Marion, OH
(now the Very Happy owner of Wurlitzer Theater 4520!!)


--- In vintagesynthrepair@yahoogroups.com, "Keith Niver" 
<kaniver@m...> wrote:
> Hi Rich
> Contact me off list and I will try and help you through this 
problem. I
> don't think it's in the keying box. More likely it might be a 
dirty chime
> switch. Does the high octave keys work above the chimes section? 
The chimes
> are a 25 note section beginning at middle C on the lower keyboard. 
It's good
> that you have the complete service manual. Does the Melodia play 
at full
> volume on the notes below middle C? Doe all the other voices play 
at full
> volume? The pizzacot and bongo voices only affect the upper 
manual. So it
> sounds like you may have two problems. 
> 
> Keith A. Niver
> Certified MITA tech
> Niver's Service Corp
> 801 Columbia St
> Hudson, NY   12534
> 518-828-0616, Bus
> 518-755-6960, Cel
> kaniver@m...
>  
> 
> -----Original Message-----
> From: richmarionohio@y... [mailto:richmarionohio@y...] 
> Sent: Sunday, March 13, 2005 6:10 PM
> To: vintagesynthrepair@yahoogroups.com
> Subject: [vintagesynthrepair] Wurlitzer 4520 Organ lower manual 
keying
> circuit problems
> 
> 
> 
> 
> I have a Wurlitzer 4520 (the theater horseshoe version of the 4500 
> series) which has one or more problems in the lower manual keying 
> circuit(s). The Melodia voice is dead from C# (key #38) upwards 
> which also affects the chime voicing and the Pizzacato and Bongo 
> percussion signals. I was told by a Wurly tech to look at "the 
> coupling capacitors on the lower manual keying circuit box" but I 
> have no idea which caps he's referring to. He's in Missisippi and 
> I'm in Ohio so it's not like he can come over and have a look. I 
> have complete schematics for the organ and some limited experience 
> in organ repairs. I would like to talk this out with anyone who 
> might be more knowledgeable with this type problem so I can get 
this 
> magnificient instrument back in full operation. Thanks in 
advance!! 
> 
> 
> 
> 
> 
> 
>  
> Yahoo! Groups Links