HELP I got an old Accordion with Midi interface

[blaze_01]

Intresting. Im still trying to get my midi turned on by bypassing the box since i dont have the box.
As shown its wire up with 3 wires. Pin2,4,5.
Ive triend sending power through the pin4(yellow) which is the (v) pin according to the common midi2usb cables.

However im woumdering if voltage is sendt in through both pins?
The guy making these powerboxes told me power was applied in both pin4 and 5?
He said data went through 4 and 5 and that power was short circuted inside between the pins.

Im a bit confused..

 

[tjw]

You can confirm whether pins 4 and 5 are shorted by checking with your ohmmeter.

I am also confused. Standard MIDI adapters do not supply power to the instrument. The V++ (pin 4) is a current source (see the diagram @happyrat1 sent you on this thread earlier). It shows that the 5-volt power source is behind a 220 ohm resistor. This will source a maximum current of 23 mA (roughly) - this current is drawn by the instrument when signals are sent from the instrument to the "MIDI in". This is a sufficient current for signal transmission but not enough to power that display and all those devices. This current would indeed, (if the diagram MIDI out were connected to the diagram MIDI in) flow through pin 4 and pin 5, and would, because of the 3 220-ohm resistors in series, allow a current of up to 7.5 mA through pin 4 and pin 5.

If instrument power is supplied by a powerbox through this connector, then its wiring and intended use is not "standard" MIDI, rather it is a proprietary connection scheme belonging to the accordion manufacturer. If you know a guy who makes the powerbox, that would give credence to his information, for sure. I'm not sure why you wouldn't just buy one of his powerboxes ??

This "current loop" is the mode specified in the MIDI spec. It is a good choice of digital signal transmission, it allows for longer cables and less interference than a signal which switched voltages.

 

[tjw]

Can you trace these wires from the MIDI jack to where they are re-attached onto the circuit board. and follow the circuit board trace to a device?

BTW - I was reading through a very old (1996) MIDI spec which states that pin 2 of the MIDI in jack should be left unconnected. This is consisitent with your observation of your first USB/MIDI adapter.

 

[customironwork]

blaze_1

I hope you have succeeded in having a playable midi accordion. If not, sorry for the late post, but...

I have used Michael Arralde Accordions for years. Located in Kent, WA. I recently secured a 60's vintage Hohner Imperator V, in which he installed midi. The unit is of his design; however, it will not work without supplying the correct voltage to the unit. He built a small power supply (110 v ac), to supply the correct dc voltage. The accordion plugs into the power supply (midi in) and the midi out goes to a sound module.

He may be able to help with this, if, hopefully, you still have the accordion. He also installed a MusicTech midi into a 6 row Balkan type Excelsior accordion (921) for me. And, 20 years ago he tuned a beautiful Crucianelli for me. His midi installation looks every bit a professional work. Probably even more so than you can purchase from a company.

At any rate, he may be able to help. Keep squeezin.'

Neil