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Prophet 5 (Rev2) Refurb


Markyboard
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Been underway with this for a couple of weeks after getting past a parts acquisition issue which I posted about elsewhere. Made a major break-thru yesterday in getting this to boot up and this morning...sound. So time to start posting. I'll add on to this thread as things progress.

 

This is a Rev2 acquired/owned by Paolo (of Synthmania) which uses the SEM VCOs, VCAs and Envelope chips, just like the Rev1. Rev 3 converted to CEMs. This Prophet was pretty much sold for parts - no boot up, sound or any sign of life other than the power switch.

 

After some research on line (not a whole lot on this rev) first thing was to rework the power supply. A common mod is to replace the transformer with a torroidal type which is more efficient and eliminates annoying buzzing sound. There's also a documented mod to eliminate the 12V and -5V secondary voltages; way less power dissipation, less heat and much simpler to just have 3 voltages to deal with. Part of this mod involves replacing the 3 programmable EPROMs with a different part. Wine Country is a fantastic resource for these (really nice people) and got the parts to me in 3 days! Mouser and Digi-Key for everything else in less than a week. Of course that's after figuring out which parts to use which is half the battle; something I was originally willing to pay for (err...I mean Paolo was willing to pay for).

 

Original power supply configuration:

Z8TVY8Xl.jpg

 

Original transformer. What you cant see here is the hot side of the a/c cord crimped underneath. Btw this is why you don't lift the ground prong:

vw3KZbml.jpg

H3qfhNHl.jpg

 

Added IEC connector - fixed power cords are not allowed:

GA1rceCl.jpg

 

Final power configuration. Notice only 3 regulators mounted/heat-sunk to the back panel instead of the original 5. Also the 2 large electrolytic caps are used as part of the power supply mounting. Finding caps with the right value and dimensions - not fun:

7syN1vKl.jpg

 

With good power now I spent about a week trying to get this thing to boot up. From my research I focused on needing the auto-tune to complete as part of the initialization. I could see all the VCO's outputting waveforms (yay!) but without a whole lot of detailed info on how the firmware works this was frustrating. I eventually saw that some of the processor derived timing signals were not happening. At this point I finally decided I needed to socket all the logic chips on the processor board allowing lifting of pins for troubleshooting and substitution where a part was suspect . Some parts were already socketed (not sure why only these). It left me with removing 30 chips and adding 3O sockets. That's when I discovered what looked to be game over with solder blobs on more than several chips.

 

Processor Board with added sockets:

IAXMcwjl.jpg

 

This representative chip compliments of past owner named "Blobert":

2T2XgWol.jpg

 

Once socket installation was complete with chips cleaned up I was still not getting this to boot up. But I could now attack where I suspected the problem might be. Turns out one of the blobicized chips had 2 failed output. Its a 74C906 Hex buffer (in case anyone has a spare) and is unfortunately obsolete/no longer available. There are several other available parts that will work in its place but I would have to modify the board to accommodate a different pin-out. Fortunately this chip had 2 spare/unused input/output pairs that with some temporary clip-leading appear to be working:

 

n1Rg0gel.jpg

 

And that's what got it to boot up. A little later replacing a burnt through resistor (X2) due to a shorted cap at the output amp and now there's sound as well. Tracks the keyboard somewhat but lots more to do. To be continued.

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Mark, you are the best, thanks sooo much!!!

 

Truly Mark has been keeping me up to date with the project with many photos, all very interesting. While I have the hobby of electronics and can do the basic stuff like cleaning pots, building pedals, fixing minor stuff etc. there is NO way I could be able to trace IC-rooted problems like a real EE like Mark can. Thank you!!! One thing I'm curious though... Mark showed only one Blobert but there were several... how is it possible that whoever worked on the board before was able to blobertize several ICs while attempting to touch up possible cold joints?? No magnifying glasses perhaps? Applied the solder with a watering can? I don't know...

 

Hey, I was checking eBay and it looks like this Texas electronics vendor offers a tube of NOS 74C906 ? (on the drop-down menu is the one before the last)

 

https://www.ebay.com/itm/74C00-Series-Integrated-Circuits-PLEASE-READ-DESCRIPTION-NOS-New-Old-Stock-I1/153704281456?hash=item23c97d3570:m:mB5UdrDvwt8u3EuPJV_Hg5g

 

I'm one of the crazy ones who think the SSM Prophets sound a bit "better' than the CEMs... there are many who say the difference is not that much / audible or just a minor "sonic flavor", but to me... there is! :D At any rate, any vintage Prophet is a good Prophet! :laugh: [and the new ones sound fab too, by the way).

 

Mark, thanks again for all this work! I already made arrangements to sell my first-born son to pay for the repair costs, so no problem there.

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I'm one of the crazy ones who think the SSM Prophets sound a bit "better' than the CEMs...

 

You are correct sir. I have owned both SSM and CEM synths. There's nothing sweeter sounding than the SSM 2040 filter chip.

Moe

---

"I keep wanting to like it's sound, but every demo seems to demonstrate that it has the earth-shaking punch and peerless sonics of the Roland Gaia. " - Tusker

http://www.hotrodmotm.com

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I have a rev. 2 which I took to a well-known tech who has done numerous restorations on these. He did the power supply upgrade and then later started selling new PS kits. Unfortunately, the Prophet would work for a short time and then develop problems. It's been in the shop for most of the last five years. I spent a lot of money and haven't gotten much use out of it. Wish I had your skills so I could fix it myself. I'll be following your progress. Best of luck.
C3/122, M102A, Vox V301H, Farfisa Compact, Gibson G101, GEM P, RMI 300A, Piano Bass, Pianet , Prophet 5 rev. 2, Pro-One, Matrix 12, OB8, Korg MS20, Jupiter 6, Juno 60, PX-5S, Nord Stage 3 Compact
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Nice work. Never had a rev2 on my bench but replacing the PSU would definitely be priority one for those things. Isolating the defective ICs in an embedded system is what separates the men from the boys, had to resurrect a few myself.

 

Those rev2s are a lot of work but well worth it. Since those precious SSMs will blow if the rails don't rise in synchrony, I hope your new PSU used independent regulators.

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Wow, wish I knew a fraction of what you know about electronics!

 

And I wish I knew to reach out to you... I had a Rev2 that I bought brand new back in the day, that fell into dis-repair. I brought it to Three Wave Music in N.Jersey many years ago for him to fix it and then help me sell it. It sat around there for over 7 years with various excuses why it didn't get done beyond a point, and eventually (I had long since moved to Hawaii which made the whole affair difficult to follow up on) he paid me for it. Didn't get what I had hoped for, but by then Sequential had released the Prophet 6 and so on. After I paid for the restoration I feared I would not get as much as I had originally hoped. Now I see that I went to wrong person. My loss. Good luck on completing it.

 

Jerry

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...Its a 74C906 Hex buffer (in case anyone has a spare) and is unfortunately obsolete/no longer available.

 

Being an analog design guy, I don't keep a lot of digital parts around. That said, I've got a couple of bins where I keep the odd bits-and-bytes kind of thing. I looked. No 74C906. Sorry.

 

Grey

I'm not interested in someone's ability to program. I'm interested in their ability to compose and play.

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Before my head gets too big (and again thanks) electronics is just another discipline. With a few exceptions (including some lurkers :wave:) most here are not trained engineers/techs; but so what? We all have a unique set of skills developed over our years of experience in school, work, hobbies, woodshedding, whatever. Here on the forum we have top-drawer pro musicians, audio engineers, writers, doctors, accountants, sales/business reps, lawyers ...you name it. And everyone contributes what they excel at. We see it every day. That"s what makes this such a cool community.

 

I"m happy to be able to apply my previous career skills to something that goes so well with my electronic music passion. It also lets me contribute something of use here and to similar minded synth geeks elsewhere. Tbh in other circles this electronics stuff is pretty basic. As with any skill most of us fall somewhere in between the regurgitators and the really talented. I think I fall somewhere far from either end.

 

No matter. Wherever your skills/talent lie share it with others. Not only is it extremely satisfying, its the only thing that endures.

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Since those precious SSMs will blow if the rails don't rise in synchrony, I hope your new PSU used independent regulators.

 

Original psu, I just recapped and replaced 3 of the original regulators and the bridge diodes. The regulated voltages are independent by original design. Unless of course I missed a large solder blob. :eek:

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I'm one of the crazy ones who think the SSM Prophets sound a bit "better' than the CEMs..

Well call me crazy then, because the SSMs absolutely sound way fatter than the Curtis!

My Rev2 has been out for years, but I seem to recall it was a power supply issue. After Wine Country stopped working on them, I put it in the case where it sits to this day.

Hmmmmm.... Springfield, VA??? How far is that from Nashville? :confused:

Don't rush me. I'm playing as slowly as I can!

 

www.stevenathanmusic.com

https://apple.co/2EGpYXK

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Before my head gets too big (and again thanks) electronics is just another discipline. With a few exceptions (including some lurkers :wave:) most here are not trained engineers/techs; but so what? We all have a unique set of skills developed over our years of experience in school, work, hobbies, woodshedding, whatever. Here on the forum we have top-drawer pro musicians, audio engineers, writers, doctors, accountants, sales/business reps, lawyers ...you name it. And everyone contributes what they excel at. We see it every day. That"s what makes this such a cool community.

 

I"m happy to be able to apply my previous career skills to something that goes so well with my electronic music passion. It also lets me contribute something of use here and to similar minded synth geeks elsewhere. Tbh in other circles this electronics stuff is pretty basic. As with any skill most of us fall somewhere in between the regurgitators and the really talented. I think I fall somewhere far from either end.

 

No matter. Wherever your skills/talent lie share it with others. Not only is it extremely satisfying, its the only thing that endures.

 

and therein lays the essence of teaching! Many kudos for not only sharing the images, but also explaining what you are doing as you go along!

There is no luck - luck is simply the confluence of circumstance and co-incidence...

 

Time is the final arbiter for all things

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I had a Rev2 that I bought brand new back in the day, that fell into dis-repair. I brought it to Three Wave Music in N.Jersey many years ago for him to fix it and then help me sell it. It sat around there for over 7 years with various excuses why it didn't get done beyond a point, and eventually (I had long since moved to Hawaii which made the whole affair difficult to follow up on) he paid me for it. Didn't get what I had hoped for, but by then Sequential had released the Prophet 6 and so on. After I paid for the restoration I feared I would not get as much as I had originally hoped. Now I see that I went to wrong person. My loss. Good luck on completing it.

 

Wow! 7 years. He kept one of my Synths for only three years. It was a rare model he didn't have so he put it on the display floor. When I would call he would insist he was going to fix it. It had a couple of fairly minor problems when I took it in. Finally after three years of his promises to get to it I went in to pick it up. He said he had done some work on it and charged me $170. When I got it home and plugged it in it didn't work at all. My mistake for not testing it at the store. I took it to another tech who found parts left inside which shorted it out. If you read customer reviews you will find a lot of other people have had similar experiences. It appears his business model is to collect $100 deposits and hold off the customer as long as possible without doing any work.

C3/122, M102A, Vox V301H, Farfisa Compact, Gibson G101, GEM P, RMI 300A, Piano Bass, Pianet , Prophet 5 rev. 2, Pro-One, Matrix 12, OB8, Korg MS20, Jupiter 6, Juno 60, PX-5S, Nord Stage 3 Compact
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Wow! 7 years.

 

Yeah, I moved away after 1 year and didn't think that was long enough to give him, especially considering where I was moving. Which is NOT the place to try to get gear fixed, or to sell it. So I let it drag on, and then I wasn't around to be able to take it back easily. Sad that is seems to be more common than I might have thought. Life lesson, for sure.

 

Jerry

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I'm one of the crazy ones who think the SSM Prophets sound a bit "better' than the CEMs..

Well call me crazy then, because the SSMs absolutely sound way fatter than the Curtis!

My Rev2 has been out for years, but I seem to recall it was a power supply issue. After Wine Country stopped working on them, I put it in the case where it sits to this day.

Hmmmmm.... Springfield, VA??? How far is that from Nashville? :confused:

 

Not that far especially since we're talking about going to New Orleans (possibly driving) when it's safe to do so. I mean as safe as it was before the virus ;). But also if you're willing to ship it here PM me. We can discuss the beery details. :cheers:

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I have not been visiting this forum enough. Wow. What. An. Awesome. Thread.

 

Mark, you are the coolest pro EE / musician. I have always been super impressed every time I've visited your house with the kinds of gear stuff you have going on there. Now seeing how you've revived Paolo's JP-8 and now the P5 is effing awesome!

 

I miss you guys!

 

Eric

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Thanks Eric- maybe by the time it"s safe to go outside again you and Paolo can do a battle of the Prophets :saber: :saber:

 

In breaking news I was working on the front panel boards today and noticed more solder blobs. As I said earlier my eyes are bad and I assumed I didn"t notice these at first on the processor board. And yet I powered it up early on and also after completing the power supply re-work. While it wouldn"t yet boot up at this point there were no issues with power, or worse smoke. It was at this point I started doing the socket install. And again today putting sockets on the front panel board it dawned on me...I know who the blobster is:

 

IT"S ME! I"M THE BLOBSTER :fume:

 

[video:youtube]

 

Turns out that all that desoldering with the trace side of the boards face up is causing the solder to drip through or just melt whatever"s already there on the component side. Never had this problem before and maybe my desoldering gun isn"t pulling enough air to prevent this? Oh well...I hang my head in shame.

 

:blush::cry:

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I have not been visiting this forum enough. Wow. What. An. Awesome. Thread.

 

Mark, you are the coolest pro EE / musician. I have always been super impressed every time I've visited your house with the kinds of gear stuff you have going on there. Now seeing how you've revived Paolo's JP-8 and now the P5 is effing awesome!

 

I miss you guys!

 

Eric

 

Hi, Eric! Miss you as well! Once this darn virus is over we need to schedule another synth meet for sure! :)

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Once this darn virus is over we need to schedule another synth meet for sure! :)

 

Agreed. The Synthmania.com headquarters would be a great location, unless all of you fellow Virginians want to come up to Maryland and visit Chez davedoerfler. :)

 

Paolo, you need to hear Eric's tragic tale about missing NAMM this past January, needs to be told over a bottle of 12 year old Scotch Whiskey, so sad. :(

 

OK, back to solder blobs. Carry on. :thu:

:nopity:
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I've had the privilege of checking out brotha Mark's workshop. He's a passionate synth enthusiast, musician, technician and overall awesome dude. :thu:

 

Brotha Paolo aka Synthmania already knows his gear in his great hands. ðð½

 

Let me know when and where the post-pandemic meet-up happens. I'm willing to host the hang in MD as well.

 

Of course, as I'm primarily a DP (digital piano) muso these days, you may want to bring a synth or choice noisemaker. :laugh:

 

I've got the PA system, food and drinks covered. :D:cool:

PD

 

"The greatest thing you'll ever learn, is just to love and be loved in return."--E. Ahbez "Nature Boy"

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Partial quote by Poalo:

 

"I'm one of the crazy ones who think the SSM Prophets sound a bit "better' than the CEMs... there are many who say the difference is not that much / audible or just a minor "sonic flavor", but to me... there is! grin At any rate, any vintage Prophet is a good Prophet! laugh [and the new ones sound fab too, by the way)"

 

I agree. As a proud owner of an original Prophet 5 Rev 3,2, I had dabbled with the earlier Prophet 5 Rev 2 in a music store when it was the current model. Sounded awesome. But I read of numerous reliability problems. So.......I waited. When the Rev 3 came out, I saved up some $$$ got a bank loan for the rest and bought a Rev 3,2 that I still own. 1981 brand new, I still have the original manual, the cassette tape, and a basic tape recorder to load the original factory sounds, if I wish.

 

It still works quite well. I only had it worked on twice. The last time I had all the KB bushings replaced, a few front panel switches, and one of the Oscillators that would not always work. I replaced the battery. I had bought the patch memory upgrade for it, but I never installed it. I thought I would keep it original in case I ever have to sell it. i have some spare parts for it too.

 

From what I remember of the Rev 2, it sounded a little "Fatter', but then I thought the Rev 3 sounded more authentic on individual string instruments, like Cello. At least to my ears. I'm amazed that it still works and it sounds great. Its been safely set up on a KB stand in my music room for the last 30 years. Its a classic.

 

 

Mike T.

Yamaha Motif ES8, Alesis Ion, Prophet 5 Rev 3.2, 1979 Rhodes Mark 1 Suitcase 73 Piano, Arp Odyssey Md III, Roland R-70 Drum Machine, Digitech Vocalist Live Pro. Roland Boss Chorus Ensemble CE-1.

 

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My only Sequential or DSI synth so far is the Evolver, but someday I hope to change that!

I have tried plugins versions over the years, some of which can float my boat pretty well.

As I recall Mark had a nice selection of hardware polyphonic goodness...

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One of the folks at the AHMW gathering brought both a rev2 and rev3 P5. Great opportunity to compare them.

 

The CEM3340 VCOs of the rev3 are more stable in tuning.

The SSM2030 VCOs of the rev2s drift more, but the SSM2040 VCFs have a more colorful resonance. That's their ace. Rev2s sound creamier too.

 

I prefer the rev2. I could fix the tuning drift of the rev2, the core of the SSM2030 VCO is identical to the Oberheim SEM/OBX which is a Dave Rossum design. I have successfully tamed OBX VCOs.

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