This classic-looking sixties combo organ was part of a whole range of Ace Tone organs (Ace Tone Corporation’s main product line), most of them still very much in demand even today. The model 9 was one of the high-end models available in the TOP series, with a wide variety of voices, a good-sounding vibrato, reverb/sustain on two voices, split keyboard for bass, bright tabs, staccato mode for the bass section, and also an optional bass pedal board. All of this with classic red tolex, chrome legs, rocker tabs and gray/white keys for the bass section.

Here’s a page from an Ace Tone catalog, featuring the Top-9 with all accessories. Image is taken from Combo Organ Heaven, a great resource for everything Combo Organ related that includes a dedicated page for the Ace Tone Top series of organs.
 

Specifications

Repair Log

 
1. Getting inside

Electronically, the Top-9 is a classic design of the era, with 12 individual oscillators and top-down divider circuitry for each of them. The engineering behind this organ is top-notch, it’s very easy and convenient to work on when doing repairs or maintenance, because all component boards are clearly laid out & easy to access. Which is good, because when I got my Top-9, it had a few problems that needed attention.

Opening the organ was very easy, only a few screws and I could pop the top open:

I always get a kick out of opening very old keyboards, because you never know what you can find inside, for example old guitar picks, or dried up insect cocoons! This is particularly true of big electric pianos like the Rhodes, or Hammond organs, but still I was amazed at the amount of stuff I found in the Ace Tone, which isn’t the biggest keyboard around. Here’s a shot of the treasures inside, which include a pretty funky vintage pencil. As for the other stuff, I don’t really know what it’s for!

 
2. No sound on Eb keys, except the highest one

This is the first thing I noticed when I tried the organ, and I knew it wouldn’t be too difficult to fix, provided I didn’t run into hard-to-find components to replace. Here’s how I proceeded to fix the problem:

First, I located the tone generator/divider board for Eb. It was very easy, the 12 boards were clearly identified, and the organ’s modular design allowed me to pull it out without removing a single screw…

The oscillator boards

The Eb oscillator board, with tuning mechanism protruding on top

Eb oscillator board, back side

Then, I proceeded to do a little signal tracing on a properly working note. Basically I used a cheap amplifier, connected one lead of its input cable to ground, and touched the other end to the various wires connected to the oscillator board, in order to heard the oscillator tones. I found that the wires coming out of the oscillator boards’ chassis carry the various octaves, as well as ground and power connections.

Doing the same tests with the Eb board quickly revealed that the octaves were not coming out of that board as they should, so I knew then the problem had to be on the Eb oscillator board itself… It’s very easy to troubleshoot, when you have a working, identical circuit next to you to compare!

I then proceeded to remove two boards, the Eb board and A, which was working properly. With crocodile clips I connected the voltages and ground, so I now had the powered boards easily accessible for more detailed signal tracing and measurements.

Two boards, ready for further testing

By studying the PCB’s signal flow, and testing at various points, always comparing with the working board, I was able to find out where I lost the signal in the defective board. I carefully inspected the components around the area, but couldn’t find any visible damage to any part.

Again, using the properly working board as a reference, I turned off the power and began taking resistance readings of various parts of the circuit, until I found a place where the resistance was much different than expected (less than 50% of expected value). I did more test around that area, which was very near the spot where I’d lost the signal, and found a shorted capacitor. On the working board, I was getting a resistance reading of 5k from that same cap, but on the Eb board, the reading was 19 ohm… I unsoldered the cap, removed it from the board and measured its resistance again: still 19 ohm. A properly working capacitor should read OL on a digital multi meter…. Culprit found!

I replaced the shorted capacitor and the problem was fixed.

One of those green caps in the middle was the cause of the problem.

 
3. Vibrato disappears

When I first used the vibrato, everything seemed to be working fine: it was strong and clear, and the speed and intensity tabs worked as they should. But after a few minutes of playing, the vibrato was much weaker than before, until I finally couldn’t hear it anymore. I turned off the organ, waited 30 minutes, and when I turned it back on, the vibrato was back… only to disappear again after a few minutes.

I began by checking the switches to make sure they made good contact. No problems there. Then, by following the traces and wires from those switches, I was able to locate the vibrato board (third small board from the right, near the vibrato tabs, see below). I found two trim pots along the way, for speed and intensity. I cleaned them with contact cleaner, turned them a bit, but the problem was still there.

I then proceeded to do a bit of research on the web about vintage organ vibrato circuits. I learned that the modulation signal is sent directly to the oscillators themselves, which is what gives the vibrato its color. A little bit more observation around the organ and I did indeed find the wires going from the vibrato board directly to the oscillators.

I also learned that some old vibrato circuits work by using a series of caps to phase shift the voltage and create the needed modulation signal. It just so happens that there were four caps of similar value lined up on the vibrato board, just before the board output. They became my prime suspects… Failing capacitors would explain why the vibrato slowly disappears instead of simply not working at all.

I decided to replace all four caps. I pulled them out of the circuit, and tested their capacitance. They were all rated at 4.7 microfarad, and all of them read correct value. They were electrolytic, so polarized. Out of curiosity, I checked their capacitance by switching the leads of my multi meter. Two of the caps gave me similar values to 4.7uf, but two others gave me an OL (my DMM’s capacitance reading is limited to 100uf). I usually get the same capacitance value, regardless of which lead is connected to which side, so I knew something was wrong.

Location of the vibrato board; the four problem caps were the white ones on the left side

I replaced the four caps with new ones, and after doing so, the vibrato came on much stronger than previously, and doesn’t go away anymore! Problem solved!

 
4. Organ is not silent with all tabs off

I noticed that, when all tabs were off, I still got sound when playing some keys. I knew this wasn’t normal, as it would mean this tone would always be blending with any other tab I had on. By comparing the sound change when turning each tab on and off individually, I was able to pinpoint the source of the problem: the ‘Mix-tone I’ tab was always on, rocking the tab on or off didn’t make any difference to the sound.

It turned out to be a pretty simple problem to troubleshoot. I just looked at the switches from the bottom, and poked around with my DMM to make resistance measurements. I found out that all the other tabs’ bottom lugs (the top ones on the picture below) were connected to ground, and so read zero ohm when checked against ground, but the ‘Mix-tone I’ read 3k. Somehow the ground connection of that particular switch wasn’t good, and so didn’t allow the tab’s sound to ‘bleed out’ to ground properly. I reestablished the connection between the tab lug and ground with a small piece of wire, and the problem went away. Simple!

The bottom of the voice tabs board; notice how the voice tabs are connected to the ground rail at the top

 
5. Other issues

I now consider my Top-9 to be in full working condition, but there are still a couple of issues I’m slightly concerned about. The first is that the majority of the green capacitors in the organ (there must be more than a hundred of them), including the one that was responsible for the Eb failure, have over the years begun to sweat. They’re all covered with some sort of oily substance that has created little droplets all over them. Now, they obviously haven’t all failed, but I wonder how much of a sign of impeding failure this means… Of course I could decide to replace all of them, but the amount of time this would entail is enormous… So for now I’ll let them be, hoping that they don’t start failing one after another…

The other concern I have is that, when many of the voice tabs are activated (especially the more bassy ones), the organ becomes gritty and distorted. Fortunately, it’s not an unpleasant distortion, so it doesn’t bother me that much. Actually, it sounds pretty cool. But still, I wonder if this is a normal feature of the organ, or if maybe the preamp section is a little busted, and I guess sometimes I’d rather have the cleanest sound possible out of the organ, so having it distort could be limiting… . I haven’t been able to A/B this with other organs, so I’m not sure how normal this is.

Apart from that, I’m very happy about the Top-9, and also that I was able to fix every critical issue it had when I first received it.
 

Gallery

The bottom of the voice tabs board; notice how the voice tabs are connected to the ground rail at the top

Location of the vibrato board; the four problem caps were the white ones on the left side

One of those green caps in the middle was the cause of the problem.

Two boards, ready for further testing

Eb oscillator board, back side

The Eb oscillator board, with tuning mechanism protruding on top

The oscillator boards