Just discovered I still had one of these at my mothers house. It was hidden away in storage. I thought I had sold it. It has been their since 1989 when I moved out.. It worked fine when I last played it. Opened it up and everything looks like the day it was made. No dust even. No burnt spots. All original. Tried to power up and absolutely nothing happens. No lights or sound. Time to get my multimeter out one of these days.
Have you experienced a lot of shorted tantalum caps? I don't do keyboard work but in my experience they are usually pretty reliable and I dont change them out like I do electrolytics.
With certain brands of vintage synthesizers (most particularly ARP, and to a lesser but still significant extent Yamaha and Oberheim) I do find a lot of shorted tantalum capacitors. Most dead ARPs I see have been due to shorted tantalums.
I'm glad you post these because I can now see other issues I have with my Omni that I didn't even realize (like staccato bass doesn't work) and when it fires up, it always starts with hollow waveform enabled... good stuff man.
The hollow waveform enabled defaulting on is common. There are 2 revision of those switch daughterboards, one with 4069s and one with 4013s. I never really paid attention, but I bet one version defaults on and the other off.
Gotcha... ok. Well I guess now I need to figure out why Staccato doesn't work. I never did the "full" restoration with chips etc, just the entire arsenal of caps...
Synth Chaser I dropped in another 4007 and nothing changed. So the switch does light but I have no idea if it's actually working correctly or not. You think it could possibly be something on the switch board itself?
For the purpose of these particular circuits, electrolytics are quite sufficient. Tantalum capacitors are needed in certain specialized situations (for example, power supply decoupling), but they are very prone to shorting out to a dead short when they wear out. Exceeding their voltage rating, even by a small amount for a very short time, drastically shortens their life. It's somewhat of a mystery why ARP used them in these circuits in the first place -- one story says ARP got a good deal on a big batch of them so they used them everywhere. And to make matters worse, the power supply in these units was prone to overvoltage spikes when turned on -- so every time the unit was powered up, all those tantalum caps got a poke in the gut, speeding them on their way to dead shorts-ville.
YAYYY! Orange pushbuttons again! Thank you, Mr. Chaser! AARRRRGGHH! The inside of that Omni looks like the lint trap in my dryer - but WORSE! Did you get the pass transistor replacement from Fry's? They stocked NTE a lot. Was my go-to parts place. AARRRGGGH!, number 2... 19:37 - Slider jetsam - GROSS! The late synth repair guru, Kevin Lightner, used to take grungy PCBs like those, and wash them under running water and Simple Green, then rinse with distilled water and dry them in a home-built drying cabinet. They didn't get damaged, and looked factory fresh in the end. PEOPLE! WD-40 DOES NOT WORK TO LUBE CONTROLS! Not switches, pots or sliders! It creates a frickin' MESS. Thank you again, Mr. Chaser! GREAT instructional vids!
From time to time I'll buy other companies' surplus, and I had acquired a lifetime supply of those NTE equivalent ARP power supply transistors that way. I've got a pretty wide selection of parts on hand--haven't been desperate enough to drive to Fry's for components in a while. :)
Ok - That makes sense. I forgot to mention All Electronics in the San Fernando Valley, as a former source of inexpensive parts. So, You Da' Man if I need another P/S series pass transistor! Thanks!
Hey Synthchaser I have a random question about the CEM 3310 chip used in the Oberheim OBX. Do you know of a modern equivalent that can be used once those chips are unobtainable?
No, but Old Crow made his own CEM3310 equivalent circuit, and has a project called CrowBX that he uses it in to make an OB-X equivalent voice card out of common discrete components. www.cs80.com/crowbx/
Thank you so much for posting this! I'm enjoying every minute of your vids:) But so far I didn't find solution to my probem :/ If I was in the States I would send you my boards for sure. So, after complete recap of my Omni2 there was still silent synth section. Filter seems to be working as I can hear clicks with max resonance. If you have any suggestion what to check, I will appreciate it. Thank you in advance!
Assuming you have no oscilloscope and just need to guess and check you might consider something like the IC kit I have on my site, changing the chips on the filter, synthesizer board, and synthesizer control board. I don't think you can assume the filter is working from how you describe it, you may just be hearing the VCA opening and closing. A common suspect would be the LM3900 on the filter. But it could be any number of things, and the best way to fix it would be to track down the problem on an oscilloscope.
How do people get their synthesizers so dirty? I always keep mine in their cases and away from dust. Some people are just nasty gross, can you even imagine how their house looks like lol
Just discovered I still had one of these at my mothers house. It was hidden away in storage. I thought I had sold it. It has been their since 1989 when I moved out.. It worked fine when I last played it. Opened it up and everything looks like the day it was made. No dust even. No burnt spots. All original. Tried to power up and absolutely nothing happens. No lights or sound. Time to get my multimeter out one of these days.
Those lit sliders are the icing on the cake. Nice work.
Your work is amazing, I'm a big fan! What do you use to clean the case, key levers and keybed?
Have you experienced a lot of shorted tantalum caps? I don't do keyboard work but in my experience they are usually pretty reliable and I dont change them out like I do electrolytics.
With certain brands of vintage synthesizers (most particularly ARP, and to a lesser but still significant extent Yamaha and Oberheim) I do find a lot of shorted tantalum capacitors. Most dead ARPs I see have been due to shorted tantalums.
What the capacitor values for the power supply you replaced them with?
synthchaser.com/product/arp-omni-2-capacitor-replacement-kit-with-4075-vcf-rebuild-kit/
I'm glad you post these because I can now see other issues I have with my Omni that I didn't even realize (like staccato bass doesn't work) and when it fires up, it always starts with hollow waveform enabled... good stuff man.
The hollow waveform enabled defaulting on is common. There are 2 revision of those switch daughterboards, one with 4069s and one with 4013s. I never really paid attention, but I bet one version defaults on and the other off.
Gotcha... ok. Well I guess now I need to figure out why Staccato doesn't work. I never did the "full" restoration with chips etc, just the entire arsenal of caps...
Assuming the switch is working and the signal is making it down to the bass board OK, most likely culprit would be Z1 (CD4007) on the bass board.
Synth Chaser awesome, I'll check it out. Looks like someone had a field day on Z7 with some jumpers.. can't wait to see what that's all about...
Synth Chaser I dropped in another 4007 and nothing changed. So the switch does light but I have no idea if it's actually working correctly or not. You think it could possibly be something on the switch board itself?
"Junked Up" is this a technical term?
How come you would replace the tantalems with electrolytics. Great work by the way
For the purpose of these particular circuits, electrolytics are quite sufficient. Tantalum capacitors are needed in certain specialized situations (for example, power supply decoupling), but they are very prone to shorting out to a dead short when they wear out. Exceeding their voltage rating, even by a small amount for a very short time, drastically shortens their life. It's somewhat of a mystery why ARP used them in these circuits in the first place -- one story says ARP got a good deal on a big batch of them so they used them everywhere. And to make matters worse, the power supply in these units was prone to overvoltage spikes when turned on -- so every time the unit was powered up, all those tantalum caps got a poke in the gut, speeding them on their way to dead shorts-ville.
YAYYY! Orange pushbuttons again! Thank you, Mr. Chaser!
AARRRRGGHH! The inside of that Omni looks like the lint trap in my dryer - but WORSE! Did you get the pass transistor replacement from Fry's? They stocked NTE a lot. Was my go-to parts place.
AARRRGGGH!, number 2... 19:37 - Slider jetsam - GROSS! The late synth repair guru, Kevin Lightner, used to take grungy PCBs like those, and wash them under running water and Simple Green, then rinse with distilled water and dry them in a home-built drying cabinet. They didn't get damaged, and looked factory fresh in the end.
PEOPLE! WD-40 DOES NOT WORK TO LUBE CONTROLS! Not switches, pots or sliders! It creates a frickin' MESS.
Thank you again, Mr. Chaser! GREAT instructional vids!
From time to time I'll buy other companies' surplus, and I had acquired a lifetime supply of those NTE equivalent ARP power supply transistors that way. I've got a pretty wide selection of parts on hand--haven't been desperate enough to drive to Fry's for components in a while. :)
Ok - That makes sense. I forgot to mention All Electronics in the San Fernando Valley, as a former source of inexpensive parts.
So, You Da' Man if I need another P/S series pass transistor! Thanks!
Hey Synthchaser I have a random question about the CEM 3310 chip used in the Oberheim OBX. Do you know of a modern equivalent that can be used once those chips are unobtainable?
No, but Old Crow made his own CEM3310 equivalent circuit, and has a project called CrowBX that he uses it in to make an OB-X equivalent voice card out of common discrete components. www.cs80.com/crowbx/
Synth Chaser awesome thanks for the reply.
Beautiful work!
Thank you so much for posting this! I'm enjoying every minute of your vids:) But so far I didn't find solution to my probem :/ If I was in the States I would send you my boards for sure.
So, after complete recap of my Omni2 there was still silent synth section. Filter seems to be working as I can hear clicks with max resonance. If you have any suggestion what to check, I will appreciate it. Thank you in advance!
Assuming you have no oscilloscope and just need to guess and check you might consider something like the IC kit I have on my site, changing the chips on the filter, synthesizer board, and synthesizer control board. I don't think you can assume the filter is working from how you describe it, you may just be hearing the VCA opening and closing. A common suspect would be the LM3900 on the filter. But it could be any number of things, and the best way to fix it would be to track down the problem on an oscilloscope.
Enjoyed watching the video! You make it look easy. Just curious, about how long would you say it actually took to do what is summarized in this video?
It usually takes me between 10-12 hours, spread over a few days to fully restore an Omni. Sometimes more or less depending on what I'm up against.
Excelent video
How do people get their synthesizers so dirty? I always keep mine in their cases and away from dust. Some people are just nasty gross, can you even imagine how their house looks like lol
A disappointing ending with everything working!
It shows the value of all the work I did to get to that point!