Johannus Allegro

[mississippi]

In our chapel we have a Johannus Allegro organ.
It worked for many years, but now we have mayby a small problem.
When the registers of the upper manual are switched off the organ workes ok.
When one ore more registers are switched on of the upper manual and the upper manual is played with, a tone is hanging.
The only way to get it lose, is switching of the organ and switching on again.
When the couple register is chosen, and playing the lower manual and a register of the upper manual is chosen,
the same happens.
Now we are playing only with the lower manual and the pedal, but this is not what we want.
I changed all the ic's from the upper manual with the lower manual, but the problem remains in the upper manual.
Does somebody have an idea ??
Regards,
Mat

[indianajo]

The most common problem in electronic devices over 10 years of age is leaky electrolytic capacitors. Many "sustain" circuits use these to hold a note on. These are devices with a minus in balls in a stripe pointing at one lead. If you have them there will be one for each key in the manual with susteain, at least. Sustain caps will probably be 10% tolerance parts or better. Electrolytic capacitors are usually larger than 5 uf (microfarad). You buy them from farnell or mouser, click passive components, click capacitors, click aluminum electrolytic. I tend to buy the ones with service life over 3000 hours, as I don't like doing jobs over again (as I have done on several pieces of equipment as the new caps wore out). In general, electrolytic caps are also heavily used in the power supply area, where they tend to wear out first because of the higher temperatures. These are aluminum cans full of a water solution, typically sealed with cheap rubber, although high end producers can buy the long life versions sealed with something better.
Jan Girardot may have a service manual. check his parts list thread on Music, accessories, or other thread. This would provide more specific guidance.
Some organs built after 1980 have custom IC's that can only be bought from the manufacturer. We ran into that on a Conn, the IC scanned the key contacts and converted the parallel data to a serial datastream that was transmitted off to another custom part.

[Jan Girardot]

Sorry, Mississippi;

I have nothing on that Johannus, but since you are right next door, just give them a call.

. . . Jan
the OrganGrinder

[mrdc2000]

mississippi,
Since you live in the country where the organ is made, why not contact the factory directly, I'm sure they know how to fix it or will tell you how.

[arie v]

Hi,

Is this an old analog organ? Have not heard of this model designation before.

Anyways, if it is an analog organ, it may be a contact finger on the swell (top) keyboard that is pulling away from the circuit board. Usually they go droopy slowly, so you end up with an intermittent cypher.

With the analog organs, they coupling between the top and bottom keyboards was through another set of key contacts on the lower keyboard. You may want to check the note on the lower keyboard as well for the problem.

How old is this organ?

AV

[mississippi]

Hi,
Thanks all for replaying.
This organ is about 15 years old. It is true that Johannus is a Dutch firma. I have also the service doc from this organ. It is a complete digital organ. That I asked the question here is because maybe somebody had the same problem I hear the highest Fis tone as a hanging tone. It only comes when the upper manual registers are swtched on an a tone played where a Fis is in on the upper manuals or the manual coupling is switched on.

[indianajo]

If the organ is 15 years old, it may be worth paying a service man to check it out. If the mechanical contact problem that Arie mentioned is true, then experience bending it back or replacing it would be worthwhile paying for. The organs I work on don't get key contact problems often.
The service manual will be copyright protected if 15 years old, but if you want to copy the relevant manual page for the upper manual processing and privately message a .gif or .pdf file to arie or me we could look at it. There may be some electronic problem but unless it uses common CMOS analog switch IC's as keying circuits, there may be no recourse but the factory tech. Tell us what IC's you replaced with the message. Don't post the schematic publicly on here.

[mississippi]

Hai Indianajo, I sent you a PM.

[indianajo]

You are in luck if there is an electronic problem with your stuck on key. The IC's are industry standard. I would start with a DVM on the input of the ULN8303, looking to see if the voltage in from the key itself goes up and down with the key, similar to one that works properly. If the input to the ULN8303 does not act the same between keys that work and keys that don't, you probably have a mechanical contact problem as Aire V said. It is remotely possible, since you are near the sea, that there is a salt bridge between two solder pads or connector parts between the key contact and the input IC, the 8303. Inspect all the wiring carefully and furthermore, wipe it down with a paper towel dipped in deionized water. Squirting the connectors etc with DI water is not wrong either, if you let it dry 24 hours before turning it on. You might have a flux bridge between 2 solder pads, this requires scraping with a steel pick before washing off. Check the diode at the 8303 while you are at it., 450 ohms with the black on line end, 1999 without (or at least higher if 8303 is still soldered int).
If the voltage goes up and down into the 8303 but the 8303 sticks on (output stays low voltage after key released) you should see it out the opposite pin. The datasheet is on datasheetcatalog.com, as is the one for the 8255. The 8303 are bjtransistor parts so don't be afraid to touch them with the power on, but don't bridge two pins with the meter probe.
I never expected to see 8255's again since they were in use on single board computers my team used on stuff installed in the JSC mission control center as long ago as 1976, but there they are, the same part. This datasheet is on the catalog too. You could see the voltage going in ID pin, but it takes an oscilloscope to see it going out. These DIP packages are numbers counterclockwise from pin 1, the one with the dot, from the top. Don't bridge 2 pins on this either with the probe. Removing and replacing a soldered in 40 pin dip is a skill, you you might want to hire an experienced computer tech to do that if you get that far. Again. salt or flux bridges in the wiring leading from the 8303 to the 8255 are again a possibility, and cleaning with water and a pick may help.
Good luck.

[mississippi]

Thanks for this information Indianajo. I will start this afternoon with measuring this all.
It would be a hell of a job because the everything is build very compactly in a tower of printed circuitboards connected together with short flat cables.
I put here the results.

[indianajo]

You may be able to get the offending PWB out to see it by building a long flat cable. Farnell.com and mouser.com have a large selection of industry standard connectors in Europe, but mouser has them better organized by catalog page (pdf file). I find a dial calipers very useful for figuring out inter-pin spacing. You may also have a local distributor whose counterperson can identify the short cable and get you the parts to make a longer one. The connectors tend to push on the ribbon, so a wide sheet matal clamp vise-grip pliers is useful to install them. Item E http://www.mcmaster.com/#metal-crimping-pliers/=hayre2
While ordering, look for a dip clip to make it easier to get a clip lead onto a dip package. http://www.mouser.com/ProductDetail/...FcnLn9H6WYwXwl
Pamona grabbers are useful for clipping the meter onto the dip clip without shorting. I believe this number has banana plugs on it for the meter but check carefully the detailed listing. http://www.mouser.com/ProductDetail/...8pgOzr7ks6M%3d

[mississippi]

Hi indianajo,

I measured both manuals and the pedal with an oscilloscope. I see the pulse train comming, ans when a key is pressed, you see the key niceley appearing and disappearing when the key is released.
There is no problem to be seen in that part.
It seems that there is no problem in scanning the registers and the keyboards.
Alle the generators for the pedals, upper and lower manuals are working correct.
Then I started to measure the pulstrains to the voicegenerators, the strobe pulses are comming when a tone is selected.
When it goes wrong one of the current to voltage amplifiers (TL074) gives an output tone (highes Fis) and will not disapear until the organ is switched off.
I changed the voice-ic with another, and it did not help.
Now I am out of ideas.

[indianajo]

Well, back to basics. Electrolytic caps dry up. You might try replacing the 10 uf electrolytic capacitor like C85 (I don't know which TL074 section is which) and the 4.7 uf electrolytic capacitor C01? the input DC blocker. The 10 uf is patently a low pass filter to keep high frequency transients off the fast slew rate TL074. There is also a power supply (+-15V) electrolytic cap on the amp PCB somewhere that is probably also dried up. C78,C79,C80 are also some kind of a filter whose inflection point has changed as the e-caps dried up. Do the caps for the TO074 section that is oscillating, first. Do the other 4 sections, later.
If that doesn't help, put a 0.1 uf ceramic cap (not film) between pin 14 and 7 of the back of the TL074 socket. TL074 is a pretty fast amp that is tempted to oscillate.
If that doesn't work try replacing C82 the .001 uf disc capacitor with the same or even a .01 uf. Although ceramics caps don't fail much, it might more likely have a bad solder joint. C82 is an anti oscillation high frequency gain killer cap.
Frankly, if that helps, replace every other electrolytic cap on the amp board, and eventually the organ. 15 years is long enough on electrolytic caps. I put 71 electrolytic caps in my h100, 6 in my ST70 tube amp, about 20 in my inherited 197? transistor FM radio that doesn't get hot, two on my 6 year old computer mainboard last month, etc, etc, etc. Buy caps with 3000 hours service life up, life is too short to replace 500 hour caps (the kind most commonly stocked in stores). over and over again. Farnell.com has the hours life in the selection table, mouser.com makes you download the manufaturer's datasheet to see the hours service life. Click passive components, click capacitors, click aluminum electrolytic. Make sure you mark the plus lead before you pull the old caps out, they blow the end out and leak if you get them backwards. If one was backwards on the original installation (possible on low volume goods) no wonder it doesn't work.
If that doesn't work try a MC33179 for the op amp, it has a slower slew rate.

[mississippi]

I will order some of those components, It will take some day's to get them.
When everything is in, then I start to change them.
I 'll be back when done. :)