jaaap
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Post by jaaap on Nov 22, 2010 13:21:21 GMT -5
A few weeks ago I saw an Farfisa VIP organ for almost free, so I just had to buy it. But it is starting to sound worse everytime I play it.
Right after I bought it the organ was perfect in tune and sounded great, but after about 20 seconds some of the notes started to sound really out of tune and distorted. But everytime I turn it on and play it those notes started to sound bad quicker.
I am really getting into electronics lately (I build some guitar effects), but I need to learn a lot. Luckily enough I did find a manual/schematic to understand the working of the organ better.
The first thing I thought about was that there where some instable resistors in the oscillator or perhaps the divider circuit. But I read somewhere that these organs don't have much problems with instable resistors.
Then I thought it might be an instable transistor, because some of the notes sounded distorted, so maybe there was running too much current to the circuits? Could that explain why it starts to sound worse each time I turn the organ on? But on the other side, some other keys sound fine.
I took of the back of the organ to inspect the oscillator circuit. I found at least one capacitor that looked leaky. Could bad capacitors cause notes to detune or get distorted?
I already looked for replacements for the capacitors in the oscillator circuit. I know what the values must be, but to be honest I don't have a clue which type of capacitor I should choose.
So could anyone give me some advice about where to start? I know I am asking a lot, but I am really excited about getting this organ back to work. It did sound really great, before it started to detune. Any help is really apreciated, because I don't know where to start.
Jaap
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Post by MusixDaily on Sept 17, 2011 17:39:49 GMT -5
Hello Jaap,
If you haven't done this yet. Start replacing the capacitators in the power supply. If they are not good they can cause any kind of problems. If you still have problems after that replacing caps in the osc's is a good idea
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jaaap
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Post by jaaap on Mar 21, 2012 14:20:29 GMT -5
Sorry for resurrecting such an old thread, but I recently started working on my farfisa again, after studying the schematics a little more.
Thanks for the advice MusixDaily. I did replace the capacitors on the power suply. That didn't change much. Maybe it reduced the very high output of the organ a bit. I decided to replace almost all of the electrolytic capacitors, since the original 40 years old made in Italy capacitors were still there. That solved some minor problems with the special effects.
I still have problems with notes that are completely out of tune, however I did find out that all the notes on the 2 highest octaves with only the 4" flute are in tune. Because two octaves on the 4" flute are in tune, I came to the conclusion that the oscillators should do there job.
I found out that the the notes generated by the oscillators, are divided in 7 octaves by a 7-stage octave divider chip. Because most of the out-of-tune notes are on the lower octaves, I think some of these octave divider chips are damaged. There are 11 frequency divider chips in the organ and I think 4 - 5 of them aren't working properly. Does anyone know if these components are likely to fail? And does anyone know perhaps a good way to find out which of them aren't working properly?
The frequency divider chips for the farfisa vip 500 (saj-1880 / ay-1-5050) are out of production, but they are still available as new old stock at 20 - 40 dollars a piece. I found them quite cheap (9 dollars) at littlediode.com (http://www.littlediode.com/components/SAJ180.html?NO_COOKIE_WARNING=2&ti=2b00ea271791420803d4587acce134c5&xid=8f6be3e9b1bee096d4a48841966bc610). Does anyone have experience with this company?
Jaap
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Post by alessandro on Mar 22, 2012 10:41:11 GMT -5
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jaaap
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Post by jaaap on Mar 22, 2012 13:16:19 GMT -5
Thanks, I checked out that website before. It is really helpful, but they don't provide hardly any info about repairing Farfisa VIP's. Most of the info is about the Farfisa Compact, which uses divider circuits in stead of divider chips.
I did read the part about finding bad dividers again and I found this: "The bad news is, if you have more than one bad divider for a given note, you can't test the lower ones until you get the ones above it working" I guess I'll just have to purchase enough divider chips and replace them until all the problems until the organ is working properly again. The first bad notes after the two properly working octaves use divider 1, 6 and 8, so I replace those first. If I have some chips left after the repair, I can always sell them or keep them as spares.
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Post by joelindsey on Mar 22, 2012 16:26:24 GMT -5
My Farfisa 345 uses the same divider chips. There is a guy who makes work-alike boards that plug into the IC socket and he sells them for $35. Can't remember the website. When I bought my 345 it actually had one of them installed. It uses two 4520 ic's to divide and a hex inverter chip to square off and sine wave inputs. It wouldn't be too difficult to build your own. The hex inverter chip is unnecessary because the oscillators in the organ put out square waves anyways.
If there are any tuning issues, I look at the oscillators first. The chips just divide the frequency they are given. The nice thing about the VIP's is they don't use those stupid tuning coils like the older organs. Measure the supply voltage at each oscillator, as the frequency is dependent on that (notice how if you hold a note down while you switch the organ off the pitch skyrockets and sounds like a laser gun). If everything on the oscillator board(s) looks fine, check the power supply.
That being said, the divider chips could be screwing with the frequency instead of dividing it in half like it should.
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jaaap
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Post by jaaap on Mar 25, 2012 14:57:32 GMT -5
Thanks Joelindsey! It indeed makes more sense to check if the oscillators and power supply are working properly before buying and replacing expensive IC's.
I assumed the oscillators worked OK because the 2 highest octaves on the 4" flute are completely in tune, but I will measure the voltage to be sure there are no problems there.
I will try to measure the power supply as well. I only replaced all the capacitors in the power supply. I have to find out how to do that though, the diagram is a bit confusing to me.
I didn't know you could replace the saj-180 IC's with other ones, mounting them on a small board. Wat would exactly be the benefit over using those old stock original IC's? I guess 4520 IC's are more common and possibly cheaper?
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Post by joelindsey on Mar 25, 2012 18:33:20 GMT -5
Yeah, the 4520's are only a few cents while the obsolete chips Farfisa used are pretty tough to find and at least $20 each. The downside is that you need two 4520's and a board to replace the one obsolete chip, so if you need several and don't care for soldering much it might be too much of a hassle.
If the two highest octaves seem fine, then I suppose it could be the chips. I would expect a "bad' chip would just stop working entirely, as opposed to just putting out an out of tune note. Are the bum notes on pitch with others? Perhaps the previous owner tried to fix it and wired some notes to the wrong key switches?
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jaaap
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Post by jaaap on Mar 26, 2012 14:18:55 GMT -5
Well the strange thing is that the organ is completely in tune when I turn it on, but after about 10 seconds 3 - 4 notes / octave will go out of tune (pitch increases or decreases to a certain level and distort sometimes). The two highest octaves stay in tune. The burn notes are in pitch with each other.
Because the organ is in tune when I turn it on, I don't think a previous owner accidental wired some notes to the wrong key. For some reason he did took out the power-switch and mounted it to the other side of the lower manual.
Because it takes a little time to go out of tune, I would suspect there is something wrong with the voltage supply to some critical parts like the dividers? It does indeed sound more logic for a IC to just fail in stead of creating out of tune notes...
I could buy just one divider chip and see if replacing it will change some of the bad notes. I have found that littlediode.com sells them for around 9 dollar, so that's not too bad.
The alternative of using two 4520 chips does sound really interesting. If the problems are caused by bad divider chips, I would think there would be more than one not working properly so it could indeed be a little bit too much of a hassle. But on the other hand, there is plenty of space for using two chips on a small board... I will surely consider this option. Thanks.
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jaaap
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Post by jaaap on Aug 25, 2012 12:26:29 GMT -5
Today I replaced the bad divider chips (saj-180). This solved all the tuning problems. So bad divider chips can be causing all kind of strange out of tune, distorted or completely silent notes.The organ is fully working now and plays in tune. Glad to bring back this old farfisa to life again.
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Post by joelindsey on Sept 11, 2012 0:55:49 GMT -5
Glad to hear it's working again! Also, good to know about the IC's screwing with the tuning.
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Post by stixsigma on Dec 10, 2012 12:54:44 GMT -5
I've finally figured out how to access all the innards of my VIP400 so it's time to start replacing things.
Where are the divider chips located on your organ and how can I identify them?
Thanks
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jaaap
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Post by jaaap on Dec 13, 2012 10:55:16 GMT -5
Hi Stixsigma, On the farfisa VIP500 (double manual) the divider chips are located under the flute filter/effects board. They are accessible by lifting this board. There is a picture on the very useful web page of Jurgen Haible: www.jhaible.de/farfisa/08farfisa_vip500_jh_drawbar_electronics_raised.JPGThe rectangular black chips just above the upper manual are the divider chips. There is "saj-180' or "ay-1-5050" in white letters printed on the chips.. They sit in little sockets, so you can just pull one out and swap it for another one without soldering. If I remember it correctly, the VIP 400 is a single manual organ? They are quite similar but I don't know if the dividers are located at the same place as the VIP 500. Good luck!
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Post by stixsigma on Dec 17, 2012 17:04:38 GMT -5
Thanks jaaap.
I'm going to have a look tonight and see if any of them are just loose. Otherwise, I'm going to get a few replacements and try that out. When I googled on those two codes (saj-180 and ay-1-5050) I found nothing that looked current.
Any ideas other than littlediode, which did not have anything in stock?
The VIP400 and VIP345 have the same features, except that the 400 is the dual-keyboard model.
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jaaap
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Post by jaaap on Dec 20, 2012 11:29:07 GMT -5
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