DSI / Prophet Forum

[psyfi]

Thought I was better off starting this as a new thread as we are now talking about another Prophet.

[rikusk]

The low key priority issue is due the rev 7.0 firmware. To get things working as you prefer you'll need 6.1c firmware. For some reason the rev 7.0 firmware lacks this feature. The rev 7.0 has more features regarding calibration and tuning so it is possible the low key priority feature has been omitted due memory space or something.

The saw wave on the S/H output is described in technical manual on paragraph 5-7. "Leakage causes the output to look like an inverted sawtooth". U354 is most probably failed. What I have learned, those old TL082s does fail quite often.

[psyfi]

I see so It is not possible to play seviral note one after the other over laping in unsion mode and have 1 envalope trigger but multiple notes trigger an envalope each time?
That is unfortunate. AS this machine already has version 7 in and as mentioned previousley on another thread version 7 requers modification tot he power supply what is invloved in reverting the power suplly to work with previous software versions?
P.S. can't find section 5-7 in my manual it only goes to 5-6 and then moves on to section 6 parts list. Thank you for pointing out another potential chip to look at I'll let you know how I get on.

[psyfi]

Also when reading from U354 should I be seeing the same readings as on U353 the OSC a in ital frequency chip? I have traced this saw wave up as far as U351 U343 ect which are related to the amp and filter ADSRs but I have no trouble with the envelopes. is it possible that this is just more leakage from U354?
Thank you so much for your help on this I'll update this thread with what ever results I have.

[psyfi]

Thanks mate. I replaced the chip this evening and the Prophet functions perfectly now.

I can now put the old one up on ebay for Spares or repair and having tested the voice board in this one can confirm that all the components on that are working so I hope to get a good price for it to help cover my losses before I have to sell my soul to the devil or the credit card company who ever finds me first.

Hooray. Thank again.

[psyfi]

Also noticed that the modulation is presant still on the Poly mod envalope amount effecting filter and pitch but not on the filter envalope amount and so guess it must relate to the poly mod filter envalope VCA. just need to track down what chip this is.
hopefully this is another TL802 gone bad.

[rikusk]

Glad to hear good news about your Prophet!

The VCA of poly mod envelope amount is common to all destinations (FREQ A, PW A and FILT) so the problem is most probably on U345 (at pin 7).

While probing the U345, I'd check all the S/H buffers, if there is still odd modulations still going on. The CPU of the P5 does not generate any modulations to the CVs so all the S/H outputs should be steady at the level set on the front panel. There is some reversed outputs, OSC CVs if I remember it right, so if you set all the pots to 10 you get different output voltages. They however all does not modulate under no conditions.

About the firmware versions and PSU upgrades. All firmware versions uses the 2708 eproms as the rev2 is made to use those. The PSU upgrade is actually just resoldering and desoldering two supply wires at PSU side. Reason to use 2716 eproms is good availability on component stores (with 2708s it's next to zero), wider range of suitable eprommers and better supply requirements. The 2716 runs without +12V and -5V and the latest CMOS 27C16s uses much less current. That's all good news to the burning hot PSU, overall tuning etc. If you like, I can send you, and everyone else forum members, the binaries of the rev 6.1c. Well equipped electronics stores usually offers burning services so getting the new eproms is easy.

When and if you put the old one to the ebay, can you post the link here? I'm bit tempted to grab it...

[psyfi]

Hi, and yes U 345 was the one I replaced this evening.
Working perfectly now.
I do still read that saw at a few point on the TL082s although I'm checking more than just pin 7 on each one. Should I see it anywhere?
Yes I will put the ebay link up on here and will also add to the listing that I have removed a couple of the TL082s from the old digital board. I should also warn any one that is interested that there is a chip out of the wood on the front just above the Sequential Circuits plate and that the large rear name plate has been partially removed. plus the silver top of the Master volume cap has come off. The silk screen is very good though and I will be selling it with the Kenton midi kit still in place, this is kit is only just over a year old and made to order. I will most defiantly be putting it up soon as I need to help cover at least part of the cost of getting this one. Hopefully with out letting to much other stuff go other. Already sold my SCI Multi-trak and a Tascam reel to reel is ending soon to. there are a few other things I may sacrifice if need be also.

Regarding the 6.1 software that would be great to get hold of the binary. I have a friend who said he can burn ROMs for me. So the PSU modification is just removing the supply weirs for +12 and -5? You don't need to change and regulators?

[rikusk]

There should be not any sawtooth on any output, pins 1 and 7 of S/H buffers.

Here's the procedure for the PSU mod:

Desolder two wires, blue -5V and orange +12V from PSU. It is possible to desolder these while the PCB is intact, thanks the double sided PCB, but you can just cut these off too. There is no point to remove whole PSU, specially if you like to spare the big Prophet logo.

The blue wire ends to pin 21 and orange goes to pin 19 of each eprom. The 2716 needs +5V on its pin 21 so solder the blue wire to +5V line. On PSU there is two places, either to same with red wire or pin 3 of the +5V regulator. Orange one is much easier. Just solder it to the GND with the black wires. You can leave unused regulatos there.

When you buy new eproms, select 27C16 CMOS versions of the chip. They draw less current than NMOS versions. It's possible to use 28C16 eeproms after the mod too. Only odd feature with 28C16s is during start-up. There is pattern of leds on, but when autotune starts they goes off.

[psyfi]

I'm not reading a saw on pin 1 or 7 on any of the S/H OP Amps now. sweet.
Looking at my PSU the modifications you discribe don't seem to have been carried out even though the version 7 roms are in place.
Can that be right? Will this cause any problems. I don't know when the version 7 software was installed on this machine or the Kenton kit for that matter whcih looks to be a very old model. its a twin board desinge unlke the modern single board voersion I have in the Other Prophet.

[rikusk]

That's normal. I doubt there's not many eprom/psu modified units. If CPU runs fine and original three supply 2708 eproms are ok, there is no actual need to do these modifications. Personally I like to do the mod, because I find this good way to improve the synth by small effort. Less extra heat makes things more stable and longer running.

I have no experience about the Kenton midi so in this area I can quess things wrong. Woud be nice to see how Kenton has figured things out though, because I'm still having plans to rewrite / modificate the original firmware code of the rev 2 to have midi and other nice features to added my most favourite synht. Due lack of time the project is still in phase of understanding and commenting the original deassembled code.

[psyfi]

Well both the Kenton kits I've used do not "unlike the the factory midi for the rev 3s" Go through the CPU in anyway. They sit between the keyboard and PCB 2. you solder connections directly to the back of a number of the program switches and on to the digital board to access the pitch and mod wheel CV also and you cut 1 trace on the digital board as well as solder on to the SSM 2040s and also connect to the volume jack on the rear panel and take your power from several point on the PSU board.
This all means that you don't have any way to load or save patches though sysex for instance but it is all pretty reversible.
My main complaint about the Kenton kit is that they access control of the volume through the rear panel jack rather then to the individual voices which means you only have a mono velocity effect on the volume which sounds wrong in most cases. The filters are controlled individually though.

[psyfi]

Just sorting out one remaining issue on the voice board of this one before I then sell it on.
I have a problem with the filter on voice one. Its not the 2040 chip or the 2020 chip as I have swapped these with other voices and the problem remain on voice 1. The issue is that the filter does not self resonate through out the full frequencey range. right now it will self oscillate through the low to mid range but not the high range. Could this be down to a bad cap or resistor around the 2040/ 2020? I also replaced the Op amp for the res feedback but this made no diffarence.

[psyfi]

The voice one filter problem was bad resistors on the resonance feedback circuit.

I should say that I've now fixed everything on this Prophet and I am selling this and keeping my original one which is almost fixed now also.

http://prophet5.org/viewtopic.php?p=2560#2560

Happy days