New member with a broken Porto Organ

[eronschrock]

Hello everyone. I am new to this forum. Please let me know if I am violating rules.

The organ- I recently bought a non-working Porto Organ. I put new fuses in it and it powered on and makes sound. The problem is, the sound is very very quiet, except for a second or two when the organ is switched on, and off. When pressing a key while turning it on, volume is instantly loud, and then quickly fades to a whisper. The opposite happens when turning it off.

I assume the problem is in the power supply. I replaced the only resistors in the power supply because they appeared damaged. This yielded no change.

I realize this is tough because I’m providing no schematic (I can’t find one). But I am wondering if anyone knows a particular part fails in this manner. There are two large 1000uf caps in the power supply, and I am wondering if one has failed. I do have replacements, but have not installed them because the leads are so much thinner than the originals, that I’m wondering if somehow I’ve misread the parts.

Any help or suggestions are greatly appreciated.

[eronschrock]

Well here’s a small strange update. Last night I powered the thing on and it had full volume! It stayed that way while I played it for about ten minutes. Then I shut it off and went to bed, confident it had fixed itself. This morning, it’s back to its old tricks!

[myorgan]

Eronschrock,

Are you sure there's not a timer on the organ (just kidding). Hopefully the techs will weigh in soon.

Meanwhile, could you find a model number to post, and that should help us help you. Thanks, and welcome to the Forum.

Michael

[eronschrock]

Unfortunately, there is no model number anywhere on this thing! No identifying numbers whatsoever.

I’m still unable to get full volume back. I’ve replaced the 1000uf caps in the power supply, and it did nothing.

Does anyone know what these small metal cans are?


- - - Updated - - -

Here’s a pic of the whole thing.

[Leisesturm]

Does anyone know what these small metal cans are?

I don't know, but they look fine to me. Obviously, its water under the bridge, but how did you come to own this instrument? Are there really no clues to its identity? The problem could easily be in the amplifier output transistors and surrounding circuitry. Rather than try to replace components of the main power supply ad hoc I think a technician (I am not!) would want to replace it outright with one that can provide the right voltages and currents. A schematic would help greatly. Failing that a positive ID via a make/model no. found somewhere on the chassis. Does it need to be said that if you cannot do either then you may have to consider cutting your losses ...

PS - FWIW this looks like your organ ...

[jbird604]

Those little metal parts are high-current rectifier diodes. It is possible that a failure of one of those could cause the symptoms you have. These diodes are a little hard to find, but I understand that they MAY be available through an automobile parts supplier, as they are similar to the diodes used in an automobile engine's charging system or inside the Alternator device.

As Leises suggests, it might be more fruitful to simply replace the entire supply with a modern switching supply that can deliver copious amounts of current at whatever voltages are required, though you might have to do some searching to get the correct voltages if they are not standard levels such as 12 volts, 5 volts, 15 volts, etc.

But I would test those diodes with a diode tester. Since you must have already removed them it will be easy to test them, and to find replacements by taking them to an auto parts store.

[Larrytow]

I can't help with locating diodes like those, but I will say that I have never seen that type / size in a automotive alternator. So I think an auto parts counter person will just say " You want WHAT ?! "

[jbird604]

Here's one on Amazon:

https://www.amazon.com/NTE-Electroni...current+diodes

But that is a "stud-mount" diode, and yours looks more like it was simply soldered in place. It's probably a very early type, but really nothing fancy about what it does. Just a heavy-duty diode.

Perhaps one like this would be the proper replacement:

https://www.amazon.com/20-Pieces-10A...t+diodes&psc=1

You just need to determine the voltage to be rectified, and how many amps will be drawn by the circuit, then get a diode that has a somewhat higher rating on both counts. These 1000V 10A units should meet the demands of almost any kind of electronic device these days.

Allen analog organs used the big stud-mounted diodes because the 14 volt supply had to supply current for all those electro-magnetic solenoids that pulled the key contact switches into place for each stop. Drawing a bunch of stops at once could place a very large current draw on the supply, thus the need for some industrial strength diodes.

But your device probably has more modest current needs, so I'd guess the 10A diodes are big enough. And no consumer device that I know of has ever used a voltage higher than 1000 volts, other than the old television cathode ray tubes.

[andyg]

And if replacing almost everything in the power supply doesn't work, then the suggestion of building a replacement power supply is a good one. If you can find out what voltages are required, then building a board with suitable voltage regulators etc should be easy enough as it seems you have the requisite skills.

[eronschrock]

Update: IT WORKS!

So, I stopped messing about and I put an ad on Craigslist looking for a combo organ repair person. I got one response; a person telling me to call third wave records in Detroit. I live in Ann Arbor. I called, and they sent me straight to their repair person who accepted the organ that day, and had it fixed two days later. The problem was two bad caps on the output board.

Thanks to to everyone for all your suggestions. And btw, I bought this on eBay. I have about $300 into it total, including the purchase and repairs. The repair guy fixed a few other issues and went through the rest of the organ too.