Search found 12 matches

by tdlunsfo
Tue Jul 16, 2019 4:58 am
Forum: HELP!
Topic: Sequential Circuits Pro One A Oscillator
Replies: 2
Views: 698

Re: Sequential Circuits Pro One A Oscillator

If anyone stumbles on this, the problem was a bad LM348 at U104 octave summer for oscillator A. Replaced it, tuned it up, and now synth sounds great.
by tdlunsfo
Sun Jul 14, 2019 8:59 pm
Forum: HELP!
Topic: Sequential Circuits Pro One A Oscillator
Replies: 2
Views: 698

Re: Sequential Circuits Pro One A Oscillator

I've been doing some troubleshooting and apparently the oscillator is working but it is really high pitched. The octave switch works but anything above the first octave is above human hearing. I've been checking the resistor values and haven't found anything out of spec. Thoughts?
by tdlunsfo
Sat Jul 13, 2019 7:47 pm
Forum: HELP!
Topic: Sequential Circuits Pro One A Oscillator
Replies: 2
Views: 698

Sequential Circuits Pro One A Oscillator

I have a pro one on the bench in pretty good condition but I am getting some odd things out of oscillator A. Pretty much I get no oscillation unless I disconnect the Mod Wheels, and place the modulation switch in "wheel". This gives me a really low oscillation that can be controlled by oscillator A ...
by tdlunsfo
Thu May 30, 2019 3:20 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

Finally got the last 3080 in and she is up and running. Looking back, if I had better access to the parts this wouldn't had been a bad repair. All these parts being obsolete definitely took some time to work through. Alas, it works again.
by tdlunsfo
Fri May 24, 2019 1:39 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

I have one coming from small bear. I thought I found a reputable source on Ebay as it was located stateside. When I went to get my money back the seller was obviously not from the USA. Lesson learned. I luckily got my money back but lost about 2 weeks messing with ebay. Honestly the chips worked wel...
by tdlunsfo
Sun May 19, 2019 10:55 pm
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

3080s were replaced. The fets were swapped out for j113's. It sounds like it is oscillating at a very high pitch (or not at all?). When messing with the VCF frequency fader the audio cuts out past three quarters. I cleaned both the VCF frequency and resonance faders. The faders on this synth are in ...
by tdlunsfo
Sun May 12, 2019 3:26 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

I did pull the 3080's. One of them is dead the other okay, found a test circuit to breadboard and verify. I went ahead and ordered a few stateside and popped in a few IC sockets. I may have the equipment to test this out of circuit. I have an audio gen, dual power supply, and an o-scope. Is there a ...
by tdlunsfo
Fri May 10, 2019 3:21 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

301's installed. Still no output. Now I can tell the VCA slider affects the gain by the noise levels. So sounds like the VCA amp works. Progress albeit small. Looks like I will need to go down the ca3080 route on the VCF now.
by tdlunsfo
Wed May 08, 2019 2:10 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

Well.. seems I am supposed to remove the caps between pins 1 and 8 if I am going to install tl082's. I think I will just wait for my 301's to get here and see. Hoping I don't have CA3080 issues especially in the VCA. More to come I'm sure.
by tdlunsfo
Mon May 06, 2019 1:08 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

I have actually already excavated mine using the video. Found 2 bad 301's confirmed utilizing a opamp test circuit. Unfortunately I didn't have any replacements so had to order some from ebay. In the meantime I tried some TL081's. It either didn't like those or I also have some bad CA3080's. Plan of...
by tdlunsfo
Fri May 03, 2019 3:38 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

Re: ARP Odyssey 2800 No Audio

I was able to jumper the VCF and had sound. Customer agreed to attempt a repair.. if it doesn't work out well go with the reproduction. Are the opamps the most common 4023 VCF failure?
by tdlunsfo
Thu May 02, 2019 3:18 am
Forum: HELP!
Topic: ARP Odyssey 2800 No Audio
Replies: 12
Views: 3127

ARP Odyssey 2800 No Audio

I have an ARP 2800 white face on the bench, 1973 model. It turns on but barely makes a sound. I have my +/-15v and electrolytics check good on capacitance and ESR. I also see a lot of the waveforms mentioned in the service manual but I am not getting anything out of the VCF pin 10. Almost identical ...