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Prophet 5 Restoration
Old 22nd January 2013
  #1
Here for the gear
 
🎧 5 years
Prophet 5 Restoration

I just recently happen to acquire a Prophet 5 in what looks to be fair shape from a friend of mine who has had it sitting in his studio idle for quite a while now. I have not yet been able to assess its condition yet as it is missing a fuse. It's also missing the fuse casing...what I assume is a rectangular box that slips into that rectangular hole in the back. Also two or three of the knobs have broken off and you can see that the plastic stems have been snapped off flush with the metal surrounding the plastic.

I will probably have a lot more questions for those of you more experienced in working on these instruments in the future but for now, does anyone know what type of fuse I need and where I can find one? And also where I might be able to find replacements for the stems?
Old 22nd January 2013
  #2
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Travst's Avatar
 
2 Reviews written
🎧 10 years
I'd suggest starting with the service manual.

You'll also want an owner's manual if you don't have one, so Google it up. Have you ever worked on a synth? Replacing the fuse isn't an issue, but is replacing pots something you are comfortable with?
Old 22nd January 2013
  #3
Lives for gear
 
🎧 10 years
first thing I would check for would be to see if it still has any of the CEM chips inside...
Old 23rd January 2013
  #4
Lives for gear
 
🎧 10 years
Having just spent a total of about 15 hours working on & restoring a rev2 prophet 5 (That hadn't worked for 15 years)
I say "I hope it's just the fuse" !!!

This one had some crippling logic (among other things) which stopped it from booting up properly.. Was a pain to find!

And to be honest, I would have spent another 20 hours unless someone online told me how to defeat the autotune procedure.

Great sounding synth, but unless it's something simple, not for the faint hearted to work on!

-You can't buy the shaft/stems, but vintage planet sells the whole pot.
(Chips for brains used to sell them also)

If you don't know how to source a fuse holder, maybe you should get someone else to source & install it.. You will be dealing with wiring that has lethal voltages.. I would not want you to make a mistake!

Best of luck!
Old 23rd January 2013
  #5
Here for the gear
 
🎧 5 years
Thanks for the words. I've never worked on a synth before but I have no fear and am really interested in learning about doing so. Thanks for the info about vintage planet! I'll consider having someone source a fuse and the holder for me I suppose. I'll let you know what happens after I find one and try to turn it on. And thanks for the good luck wish!
Old 1st February 2013
  #6
Here for the gear
 
🎧 5 years
So I located the fuse stuff and turned the synth on. The light on the switch goes on but none of the front panel lights turn on... it also makes a whining noise. It sounds one tone that doesn't change pitch and neither the keyboard nor the front buttons respond to anything. Any ideas? I suppose it's time to study the tech manual.
Old 1st February 2013
  #7
Gear Maniac
 
🎧 10 years
First thing I would do is rebuild the power supply, replace all the electrolytic capacities on the power supply.
Old 1st February 2013
  #8
Gear Maniac
 
🎧 10 years
Whining noise could be power supply transformer.
Old 1st February 2013
  #9
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conanb's Avatar
 
🎧 5 years
Sorry to go a little off topic but as the Prophet 5 is being discussed I just wanted to ask, is it a mono synth? I only see one audio output on the back.
Old 1st February 2013
  #10
Moderator
 
Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
See if this is of any help:

https://www.gearslutz.com/board/elect...storation.html
Old 1st February 2013 | Show parent
  #11
Gear Guru
 
Yoozer's Avatar
 
1 Review written
🎧 10 years
Quote:
Originally Posted by conanb ➑️
Sorry to go a little off topic but as the Prophet 5 is being discussed I just wanted to ask, is it a mono synth? I only see one audio output on the back.
Several bigger analogs are mono - stereo usually implies splitting/layering features or, in the case of for example a Juno-60, chorus. Jupiter 6 for instance is mono, JX3P is stereo. OB8 has left/mono/right outputs, because you can pan each voice left or right on the synth itself, which is pretty neat.

Making them stereo by duplicating the signal left and right would not be of much use on the synth itself.
Old 1st February 2013
  #12
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conanb's Avatar
 
🎧 5 years
So on the P5 you split the mono signal?
Old 1st February 2013
  #13
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Yoozer's Avatar
 
1 Review written
🎧 10 years
If you want to do anything to it, sure. Otherwise, why not keep it mono?

Not every signal has to be in stereo, only when it makes sense to do so.
Old 2nd February 2013 | Show parent
  #14
Moderator
 
Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Quote:
Originally Posted by conanb ➑️
Sorry to go a little off topic but as the Prophet 5 is being discussed I just wanted to ask, is it a mono synth? I only see one audio output on the back.
The reason why stereo field was introduced to synthesizers was addition of panoramic effects. Be it a chorus or simple panorama effect such as automated pan (i.e. ESQ-1), or individual voice panning (i.e. OB-X). Hence the stereo output.

Once digital effects came into game (such as a reverb) there was no question - output HAD to be stereo - that became "default". This is how we got stereo synths - though in nature many of them are monaural.
Old 2nd February 2013
  #15
Here for the gear
 
🎧 5 years
Thanks Don for the link. Actually I should be a little more specific... the whining noise was not from the machine itself but rather from the output when plugged in to an amp. So just the switch light turns on, no front panel lights turn on and it whines when amped.
Old 3rd February 2013
  #16
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Radishes ➑️
Thanks Don for the link. Actually I should be a little more specific... the whining noise was not from the machine itself but rather from the output when plugged in to an amp. So just the switch light turns on, no front panel lights turn on and it whines when amped.
Failure to boot up could be multiple things.

- A non working power rail
- lockup failure of autotune routine
- A billion other possibilities


If it was me, I'd disconnect the power supply from the main PCB and measure all the rails & ensure they are all working.

Watch out as you are dealing with lethal voltages near by. Please don't die!

Report back

Depending on the REV you own (Rev 3?) you'll have different rails.

+5
+15
-15

(I can't remember if a REV3 has -5v but the rev 2 does)

Regardless, on the power supply PCB all the rails are labeled.
Old 3rd February 2013
  #17
Here for the gear
 
🎧 5 years
It's a rev 2. So what exactly does testing the power supply mean? I assume you mean to make sure the connections on the power PCB are good? And I suppose I would need a voltmeter for that.
Also, I always people replacing the capacitors on the boards. I still have the older ones in... there are about 4 blue ones right up front on the power PCB. Should I go ahead and replace those guys? How do you know what type to get? I suppose those specs are found in the service manual?
Old 4th February 2013
  #18
Lives for gear
 
🎧 10 years
If you don't know what I mean, trust me.. This is not for you.

Some of the most experiences keyboard techs avoid working on prophet 5's

I have just spent over 10 hours fixing a rev 2 and I know what I'm doing!
(not including the 15 hours just studying the schems + service manual)

It froze on startup = failed autotune.

Fault was a faulty logic IC (damn hard to find)
Then the -5v failed.
After finding & fixing them (8 hours of bench time) it would boot up.

Now I can at least boot it up.. But it's horribly out of tune.

LFO is dead - dead opamp + dead SSM VCO

Knob response is screwy (faulty comparator)

Finally everything is working

Just needs a tune / calibration = 30 trimmers to adjust

See what I mean?
Old 4th February 2013 | Show parent
  #19
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exwel's Avatar
 
🎧 10 years
Quote:
Originally Posted by Futureman84 ➑️
If you don't know what I mean, trust me.. This is not for you.

Some of the most experiences keyboard techs avoid working on prophet 5's

I have just spent over 10 hours fixing a rev 2 and I know what I'm doing!

It froze on startup = failed autotune.

Fault was a faulty logic IC (damn hard to find)
Then the -5v failed.
After finding & fixing them (8 hours of bench time) it would boot up.

Now I can at least boot it up.. But it's horribly out of tune.

LFO is dead - dead opamp + dead SSM VCO

Knob response is screwy (faulty comparator)

Finally everything is working

Just needs a tune / calibration = 30 trimmers to adjust

See what I mean?
+1
I had 2 p5 rev 2's and 1 rev 3.
I really liked only the rev 2 but man i paid big money to restore it and keep it to work.
I had a original rev 1 case made with hawai maple wood..
Sold everything.
Old 4th February 2013
  #20
Here for the gear
 
🎧 5 years
Thanks for the advice. I was considering bringing it in to someone to have it done. I'll probably do a bunch of the work I know that I can do like replacing the pot stems that are sheared off and doing a thorough cleaning of the keys. Is there anything else I could do that is not too terribly challenging? like maybe those capacitors?
Old 4th February 2013
  #21
Lives for gear
 
🎧 10 years
The tantalum capacitors on the power board should be replaced.

(google what they are)

Look at the values on them, and note they have a polarity (a side marked with a +)

Get the same value capacitance with same or higher voltage rating.

10uf @ 25v can be substituted with 10uf @ 35v etc..

But even better than that, learn how to use a multimeter! Heaps of YouTube videos. Then check the power supply rails.
Hunt down a competent tech.. Ask if they have worked on a P5.. If not, keep looking!
Old 4th February 2013
  #22
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dougt's Avatar
 
🎧 10 years
If you are in the US send it to Greg Montalbano (analogsynthservice.com). He's the P-5 expert and got my Rev 1 working 100% for around $200.
Old 5th February 2013
  #23
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Xero's Avatar
 
🎧 10 years
Honestly, rev2's are definitely not a very good first project at all. It's quite a challenge. Just a synth that can be littered with various issues. At the very least, be prepared for cold solder joints all over the place, especially on the cpu board. Just reflow the whole damn thing if you can't find the cause...

if the rev2's first voice won't auto-tune, the whole synth will hang on boot. This means nothing lights up and the synth just does nothing. You can get around that by unplugging the big fat ribbon cable on boot and plugging it in afterwards. That's like, major rev2 trick number one right there! I think you can also achieve the same by bending the last pin, but I'm not sure I'd recommend that method. However if it's whining on boot and not playable at all, I'd probably avoid turning it on until you can make sure the power supply isn't totally bonkers! You don't want it frying those SSMs! Once you can confirm the voltages are stable, then this is the first thing you should try if it's still hung on boot.

IMO, all rev2's should be upgraded to 2716 or 2816 eproms/eeproms, and this lets you remove 2 of the regulators from the power supply, reducing the heat output a lot. Many "popular" techs do this mod, but it's well documented. Sequential even did a similar mod on later rev3's when upgrading rev 3.0s to rev3.1 or higher. I've documented a bunch of my p5 rev2's upgrade/repair adventure, it actually went into the shop "mostly working" but it was actually locking up and resetting on occasion, it turns out this was all from numerous bad solder joints on the CPU board, and my tech reflowed a large portion of it. This was my work list for him:

http://www.xero.cc/p5cass/todo.txt

I've got a bunch of other useful p5 documents in that directory as well, including information about performing the cassette mod on a rev2 (if yours doesn't have it) and power supply upgrades. The power supply upgrades done on mine are a little above/beyond the standard eprom upgrade/regulator removal mod. It's basically the work/ideas of Riku from www.analog.fi and it significantly reduces the heat to the point where it's essentially not even a concern anymore. It does this by using a new tranformer manufactured by the same company as the original which is a perfect drop in fit:

http://www.xero.cc/p5cass/powersupply.txt

Any good tech can probably perform these mods, so don't be afraid to use someone more local if they are comfortable working on something like a rev2. Greg M is well regarded, but I ended up using my local tech because I didn't want to ship my rev2 3000 miles across the country. Rev2's are finicky beasts compared to rev3.x, so this is definitely something to make sure you mention to any tech before you just say "my prophet 5 has issues"....some will run away from rev2 but not rev3. However, I think my tech took it as a challenge!

You may want to check out my rev2 vs rev3.3 thread as it documents some of the repair process, and a few other fellows in there also had work being done on their rev2's, so it might give you some other leads/ideas.
Old 6th February 2013 | Show parent
  #24
Gear Maniac
 
🎧 15 years
Quote:
Originally Posted by Don Solaris ➑️
Hey Don ! a very nice restoration project ! Looks awesome

Radishes, you may also want to take a look at my P5 restoration thread posted a few years ago on the HC forums:

Prophet 5 with a missing power supply... - Harmony Central

as a matter of fact, it still suffers from keyboard contact issues. I wonder what would be the best way to restore it... afaik the contacts are originally gold so they should not be scrapped (too late for that...). Will just alcohol rubbing suffice ?
Old 7th February 2013
  #25
Here for the gear
 
🎧 5 years
Hey, thanks very much for taking the time to give me help and advice on the project! I'll keep you posted!
Old 7th February 2013 | Show parent
  #26
Gear Addict
 
🎧 10 years
Quote:
Originally Posted by Xero ➑️
Honestly, rev2's are definitely not a very good first project at all. It's quite a challenge. Just a synth that can be littered with various issues. At the very least, be prepared for cold solder joints all over the place, especially on the cpu board. Just reflow the whole damn thing if you can't find the cause...

if the rev2's first voice won't auto-tune, the whole synth will hang on boot. This means nothing lights up and the synth just does nothing. You can get around that by unplugging the big fat ribbon cable on boot and plugging it in afterwards. That's like, major rev2 trick number one right there! I think you can also achieve the same by bending the last pin, but I'm not sure I'd recommend that method. However if it's whining on boot and not playable at all, I'd probably avoid turning it on until you can make sure the power supply isn't totally bonkers! You don't want it frying those SSMs! Once you can confirm the voltages are stable, then this is the first thing you should try if it's still hung on boot.

IMO, all rev2's should be upgraded to 2716 or 2816 eproms/eeproms, and this lets you remove 2 of the regulators from the power supply, reducing the heat output a lot. Many "popular" techs do this mod, but it's well documented. Sequential even did a similar mod on later rev3's when upgrading rev 3.0s to rev3.1 or higher. I've documented a bunch of my p5 rev2's upgrade/repair adventure, it actually went into the shop "mostly working" but it was actually locking up and resetting on occasion, it turns out this was all from numerous bad solder joints on the CPU board, and my tech reflowed a large portion of it. This was my work list for him:

http://www.xero.cc/p5cass/todo.txt

I've got a bunch of other useful p5 documents in that directory as well, including information about performing the cassette mod on a rev2 (if yours doesn't have it) and power supply upgrades. The power supply upgrades done on mine are a little above/beyond the standard eprom upgrade/regulator removal mod. It's basically the work/ideas of Riku from analog.fi and it significantly reduces the heat to the point where it's essentially not even a concern anymore. It does this by using a new tranformer manufactured by the same company as the original which is a perfect drop in fit:

http://www.xero.cc/p5cass/powersupply.txt

Any good tech can probably perform these mods, so don't be afraid to use someone more local if they are comfortable working on something like a rev2. Greg M is well regarded, but I ended up using my local tech because I didn't want to ship my rev2 3000 miles across the country. Rev2's are finicky beasts compared to rev3.x, so this is definitely something to make sure you mention to any tech before you just say "my prophet 5 has issues"....some will run away from rev2 but not rev3. However, I think my tech took it as a challenge!

You may want to check out my rev2 vs rev3.3 thread as it documents some of the repair process, and a few other fellows in there also had work being done on their rev2's, so it might give you some other leads/ideas.
There's some good information here, but it leaves people with the impression that all Rev2s are problematic. This is not necessarily so. I have four of the Rev2s collected at various points across the past twelve years, and after an initial restoration of about $300-$400 each by Greg M they've worked fine (still have all of them). None of them have ever had any notion of cold solder joints.
Old 7th February 2013 | Show parent
  #27
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Xero's Avatar
 
🎧 10 years
Quote:
Originally Posted by Rangoon ➑️
There's some good information here, but it leaves people with the impression that all Rev2s are problematic. This is not necessarily so. I have four of the Rev2s collected at various points across the past twelve years, and after an initial restoration of about $300-$400 each by Greg M they've worked fine (still have all of them). None of them have ever had any notion of cold solder joints.
I wouldn't be surprised if Greg M just reflows all the joints! But who knows for sure. I think part of the cause of the issue is that many of them were toured around, and the boards aren't mounted in the best of ways, so they're prone to shock. Bad joints and sockets are a common theme with these things, so even though you personally haven't had any issues, it's still worth knowing about. After repair my rev2 has been very reliable, so I'm not putting it down by any means! Especially after the power supply upgrade, it's actually running much cooler than my rev3.3 now.

I also don't think these are any kind of problems you wouldn't expect on any other 30+ year old synth. My rev2 was made in 1979, that's 34 years old now...older than me! There aren't that many polysynths older than this.
Old 7th May 2013
  #28
Here for the gear
 
🎧 5 years
I did some minor work on the Prophet but decided to take it in to get it troubleshooted by someone better than me. Does anyone know of any techs in the Philadelphia area? I took it to someone out in Ardmore and he said it might be deeper than what he is willing to dive into. Anyone else out here that works on the Sequential Circuits boards?
Old 7th May 2013
  #29
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Xero's Avatar
 
🎧 10 years
Yes! I've heard of that guy in ardmode, but he seems more of a tape/amp repair guy...My rev2 was worked on by Tim over at Website Home | Retro Linear. He's slow, but he does good work. You can let 'em know Jordan sent ya if you'd like...I had extensive modifications done to my p5rev2 from him. If you'd like to see the list of what I had done, see here: http://xero.cc/p5cass/todo.txt

My powersupply was completely rebuilt and the synth modded to no longer require the +12/-5v supplies by swapping the old 2708 eproms with 2716s. That should really be done to any rev2.
Old 28th March 2014
  #30
Gear Maniac
 
🎧 5 years
does anyone know what would cause a panel switch ( with led ) to go a bit inter mmittant ( doesnt click now but does turn on and offer with a good tap and the led works fine ) ? do i need a new switch ?
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