Repairing Frank Zappa's Delay

Seriously, I am so not worthy...

I few weeks ago I had the pleasure of meeting a fine Canadian fellow who haunts some of the wretched internet gear forums where I waste altogether too much time. I extended an invitation for Poops (as he his known to most of the world) to drop by beavis labs as he is a) a certifiable gearwhore and b) probably one of the most dedicated and knowledgeable Frank Zappa fans I've ever had the pleasure to know. So since I am a huge Zappa fan, it was a great visit to look forward to.

For the visit, Poops told me he would be bringing me a non-working ADA Digitizer 4 digital delay that he would like me to take a look at. Now I almost never do repairs. Unless it is something simplelike "You forgot to plug your guitar in,that will be $20 please" type ofarrangements, I just don't want to go there. But there was a twist.

Poops claimed this digital delay used to belong to Frank Zappa.

Now we've all heard these stories before, or seen the ultra-rare TubeScreamer on eBay that was used by both Johann Sebastian Bach and Jimi Hendrix. But I knew Poops wouldn't claim such a thing if he couldn't back it up. The appointed meeting time arrived and so did Poops. Tucked under his arm was a big shipping box. We looked it over and he pointed out the original return sticker:


Poops gave me a little of the back story where a friend of his had bought some gear from an auction that dweezil had done some years ago, apparently to thin out the Utility Muffin Research Kitchen's non-working or extra gear. Apparently UMRK is kept running as an active studio, and not some mausoleum to the great One. (Which is pretty cool in and of itself!) That friend had then gifted it to Poops because of Poops' incredible love of all things Zappa.

I promised Poops that I would give it a look but made it clear that I am not a certified repairman, but rather, a certified lunatic. I did promise that I would do nothing untoward given the historic nature of the artifact. Fast forward to last night.

First the unboxing:

Popping the Top

Next step, carefully remove the top. What would be inside? Perhaps a secret message from the Zappa himself? Or at least some vintage mojo dust from the studio where some of the greatest music of all time was recorded? Top off:

Click Here for a Huge-Ass Version of thisPhoto


What glory! The pinnacle of 80's engineering, and nary a single SMD part to be found. A glance at the lower right corner of the board revealed this:


Check it out! It is a Zilog Z80 microprocessor. The same part that powered my first computer, the indomitable Sinclair ZX81. Folks, this is old school, no fancy ASICs, SMD or Chinese Glue Gun wads, just an old 8-bit MCU and an assload of discrete logic chips.

So on to the Repair Attempt

As I lack the skills, time, or knowledge to do in-board component level debugging, I had to go with the obvious stuff. When plugged in and powered on, the power light would go on. Also when I plugged in a guitar and adjusted the input level, the LED VU bar meter would light up. All other lights were non-operational and none of the buttons worked. And it didn't pass any sound.

First step was to carefully unseat and re-seat each of the chips that were sockected. I used an anti-static wrist strap so as not to damage the unit. After the resocketing of the chips, and quick reboot, the unit would pass a signal and a few random segments of the LED would light up. But not much else. So on to the wire connectors. I removed one at a time and gave each a tiny shot of contact cleaner, being careful to do it with a cloth between the part being sprayed and the unit itself. After each one of these was done, I rebooted again.

Major success! The unit powered up, the LED display said "ADA" and most of the buttons worked. I grabbed my guitar and was greeted by a classic 80's chorus sound. Now I was getting quite excited because I'm a geek and, well, you know, the whole Zappa thing.

But several of the key buttons were still not working. So out with the multi-meter. I checked all of the connections between the display/button PCB up front and the main board. I was led to one connection that wasn't passing electrons. A quick fix-up of a single solder joint, another reboot, and 100% functional. And the sound was pure-80's divine. This unit has an over the top LFO for modulation and also has a phase option. What fun.

Here is my son Frank Vincent (as in Frank Vincent Zappa, natch) adjusting the delay time as I play.


The Dead Battery

Unfortunately the lithium coin battery that was soldered to the original board had expired sometime long ago, and taken any Zappa Preset History with it. I can only imagine what hidden gems would have lurked in there...

Yeah, I Guess I do have to Send it Back

The sad part will be boxing this up and shipping it back to Poops. He has a piece of history there. And one that he can now play. That sadness however, is easily overshadowed by the fun of being able to fondle and fix a small piece of Zappa lore.





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