The Prophet 600 Panasonic keybeds often have problems with dead or intermittent key contacts. In this video I show you how to access the key contacts, and how to repair them for reliable long-term operation.
Author: synthchaser
Cold Solder Joints
I was working on an ARP Omni 2 and came across a really bad soldering job. Someone had replaced the gating capacitors, but all of their solder joints were “cold solder joints”. What’s a cold solder joint? Well, first let me explain what a good solder joint is. With a good solder joint, both the pad on the circuit board and the leg of the component you’re soldering are sufficiently clean (both clean before soldering and from the flux in your solder) and hot for the solder to form a solid bond between the two parts you’re soldering. A good solder joint looks nice and shiny, like my work on this ARP Omni 2 below:
Now that we understand what a good solder joint is and how it’s made, we can understand that a “cold” solder joint is made when the two metals are not sufficiently heated or clean enough for the solder to truly bond between both metals. In a cold solder joint, the two parts may be stuck together, but may not have good electrical contact, and since the solder is really just a blob sitting on the surface of the pad or component, it’s very prone to crack or break off. You can typically spot a cold solder joint by its dull appearance, like I saw in the ARP Omni 2 below:
On the closeup photo you can really see the dull solder blobs just caked onto the pads and leads of the capacitors. And to no surprise, several of them just cracked off when I was going through removing and replacing all these capacitors.
Hopefully this explains what a cold solder joint is and how to spot one. To avoid making them yourself follow the following Synthchaser tips:
- Clean all surfaces before soldering
- Use flux cored solder
- Make sure your soldering iron is at a high enough temperature (typically for synth rework I use around 700 degrees F)
- Tin your soldering iron tip before soldering a part (apply a small amount of solder to the tip of the iron)
- Position your soldering iron tip so it touches both the pad on the circuit board and the component and allow a little bit of time for both to get sufficiently hot
- Feed the solder onto the component or the pad, not the tip of your soldering iron
If you find yourself melting the solder on the tip of the soldering iron, or “painting” solder onto the component from a blob on the tip of your iron, you’ll probably wind up with a cold solder joint.
Hopefully this helps, please comment if you have any other tips to avoid cold solder joints that I missed!
Synthchaser #080 & 081 – ARP Odyssey Restoration & Repair
First, we restore a dead ARP Odyssey. Not the new Korg one, a real vintage, 1973 Mk 1 Model 2800 Whiteface ARP Odyssey. We change the ICs, capacitors, sliders, repair a dead oscillator and a damaged power supply. This Odyssey gets the full Synthchaser spa treatment!
Then, we use that ARP Odyssey as a test bed to fix a customer’s Odyssey oscillator board.  Customer was reporting his Oscillator 2 couldn’t be calibrated and was drifting. The trimmer should be adjusted to make a 20Hz square wave, but the lowest it would go was 40Hz. What I saw was cool enough that I had to edit it into a Synthchaser video!
Synthchaser #079 – Oberheim OB-8 Dead & Intermittent Key Repair
Most OB-8’s use a different style of keybed than found on other OB’s. These keybeds often have problems with dead or intermittent key contacts. In this video I show you how to access the key contacts, and how to repair them for reliable long-term operation.
This OB-8 is for sale:
Oberheim OB-8 Analog Synthesizer Keyboard w/MIDI & Page 2 Serviced – Excellent!
Synthchaser #078 – Oberheim OB-8 Voice Board Repair
A customer sent a broken OB-8 voice board in for repair. We locate and repair a damaged trace, replace an incorrect capacitor and test it out in one of my OB-8’s.
Synthchaser #077 – ARP Omni 2 Phaser Repair
In wrapping up the restoration of an ARP Omni 2, I noticed the sound was ever so slightly off. Together we track down the problem and repair the culprit delay line on the phaser board of the synthesizer.
Shows the importance of replacing all of those tantalum capacitors with my kit:
ARP Omni 2 Capacitor Replacement Kit with 4075 VCF rebuild kit
Synthchaser #076 – ARP Omni 2 Wood Side Panels
I was restoring an ARP Omni 2 and one of the leather sides was damaged, as they often are, so I made some replacement side panels from hardwood. In this video I pop them on we see what it looks like when it’s done. My video camera is lousy, and doesn’t do the wood justice, but you can see the panels better in the stills at the end.
I don’t currently plan on stocking these, but if you’re really interested in a pair, contact me, because it turned out so nice, I’m sure I’ll be making more.
Synthchaser #075 – ARP Omni 2 Repair – Bass Note Problems
I troubleshoot and repair a couple of problems with this ARP Omni 2. First the lower bass voice is dead. Second, a weird problem with the low note priority circuitry of the bass notes is seemingly allowing more than 1 bass note through at a time.
Synthchaser #074 – Yet Another LinnDrum Repair – Troubleshooting Dead Drum Sounds
In case you didn’t get enough LinnDrum repair excitement last week in Synthchaser #072, I’m back at it again, firing up a customer’s “Wildcard” LinnDrum, which was purchased in unknown condition and without a power supply. We troubleshoot and fix some dead and incorrect drum sounds and give yet another LinnDrum a chance at life.
Synthchaser #073 – ARP 2600 Tonus Logo Repair – Sliders & Connectors
The greatest synth ever, the ARP 2600, is beating the heat in the Synthchaser workshop and getting a little love and minor TLC. I replace a broken slider and identify and replace some bad connectors that were causing the keyboard control voltage to glitch or be dropped.
