Rodgers 645 keyboard and stop matrix schematic needed

**stevendethick** · 08-01-2012, 12:15 PM

Hi all,
I am new to the forum. I have a Rodgers 645 with factory MIDI, however the MIDI board seems to have failed and I need to have a new encoder designed. I am basically clueless without a schematic, and support for Rodgers is pretty thin on the ground here in Australia!!

I have no need for the existing Rodgers analogue sounds as I use Hauptwerk, but without MIDI I have a silent organ. Does anyone know if the original Rodgers keyboard and stop circuit boards (with blue 16 pin ribbon cables) can be used with aftermarket MIDI encoders? Failing this, does anyone know where to obtain schematics?

Below are pics of the keyboard encoders, cables and stop boards.Manual layout.jpg Manual ribbon cables.jpg Stop key layout.jpg Stop key matrix.jpg Typical cable termination.jpg

Thanks in advance from Down Under

**John Kinkennon** · 08-01-2012, 03:17 PM

This appears to be an SPI interface which might be compatable with a MidiBox core module. The pullup resistors and the use of one IC per every eight keys fits that pattern. Also the five wires that connect the two PCBs together suggests SPI. What is the part number on those 8 ICs? Couldn't quite read it in the photo.

**PeteKnobloch** · 08-01-2012, 10:23 PM

The IC's are 4021 shift registers. The Rodgers electronics supply the Load and Clock signals from its CPU card. The clock period on the model I evaluated was 13us with the Load coming every 1.5ms. The Midibox would probably work if it drives the load and clock lines. But if you want the original organ electronics to work, Midibox would have to be changed to monitor the Load and Clock lines rather than drive them. Another issue is that the 4021's are running on 12 volts rather than 5v.

Pete

**John Kinkennon** · 08-02-2012, 02:41 AM

Thanks for the info, Pete. Personally, I'd pass on trying to reuse the boards if they use older CMOS chips. It would be a reasonably simple design project, but there won't be an off the shelf product that will just plug in and work. So a repair might be the best option. What's the lone 9th IC? Any chance that it's a buffer IC of some sort or would it be part of their multipexing scheme?

If someone sends me a sample keyboard or even just the PCBs I'd be willing to design an interface to some "standard" encoder, perhaps the MidiBox core module since that's so affordable and is commonly available.

EDIT: I'm always looking for a project!

**stevendethick** · 08-02-2012, 09:08 AM

You guys sure know your stuff!! Thanks for the replies! Please clarify for me ......reading your comments, can I assume that the original keyboard and stop encoders can be used through a MIDI curcuit board to generate data to my computer? I have no desire to retain any of the Rodgers analogue sounds, CPU, or power supply or audio system as I only ever use Hauptwerk anyhow.

I have opened the CPU and the socket where the daisy chained keyboard data cable is marked x2, the single one from the stop rail is marked x1.

How do you guys think I should proceed?

**John Kinkennon** · 08-02-2012, 02:13 PM

The quick fix would be to locate a service manual and get the MIDI circuits repaired. Jan Girardot may have a manual available for sale, or you could probably locate one via the internet or directly from Rodgers. There may be a simple power supply issue affecting the entire console.

If the fix isn't simple then I wouldn't hesitate to do a major swap to new MIDI hardware. Obviously this depends on how one feels about the original console sounds. That's a choice for the owner of the instrument to make -- in my case I drew a line at Allen's MDS vintage and resold an MDS-5 console rather than pull the original electronics.

If you end up considering new MIDI hardware then I'd look at bypassing the CMOS chips. I'd pull them and keep the pullup resistors. One could convert the keying to a lower voltage or use voltage dividers to get 5v or even 3.3v for modern encoders. There are a lot of encoder choices on the market, and if you're really wanting a DIY challenge try building one of my free designs on a prototype board. But try the repair route if possible -- much easier.

**PeteKnobloch** · 08-02-2012, 03:29 PM

The extra IC is a schmitt trigger buffer for the Load and Clock signals. You can use the 4021 IC's on 5 volts but the timing to and from the chips will change. I don't know about if the buffers will work on 5v. Last year I was in the process of building a small board that would clip onto the 16 wires going to the keyboard stack and provide Midi Out for the 3 keyboards. This project got delayed because the people who have the organ go back to Canada for the summer.

Pete

**PeteKnobloch** · 08-03-2012, 03:28 PM

Originally Posted by stevendethick

... can I assume that the original keyboard and stop encoders can be used through a MIDI curcuit board to generate data to my computer?

From the keyboards it can happen. The 16 wire cable allows for the 3 keyboards only. The pedal and stop data will have to come from other cables in the organ. As far as the stops I was wondering if your Rodgers 645 used LED's to indicate if the stop is on? This type of stop tab has a spring return that brings the tab back up which generates a signal like a momentary switch would. The LED indicates whether the stop is On or Off. If this is the case, then the controlling of the stops will be much harder to implement without more hardware and special software.

Did the original Rodgers Midi send Midi messages for the changing of the stops? If it did, it might be better to get the original board fixed rather than adding something new.

Pete

**John Kinkennon** · 08-03-2012, 10:05 PM

For what is possible I'd suggest taking a look at the Rodgers 645 conversion described in the photo section on the Hauptwerk forum. Also, check out my own Allen console in the photo gallery on this site. My Allen 603-D with added third manual includes a fully functional capture system with moving drawknobs, all at an investment that has just passed the $600 mark! That's the console without a computer and sound sytsem of course. Since I already have a computer and a fair selection of PA equipment my budget really was around $600 including the trailer that I rented to move the beast.

It's hard to suggest anything beyond the repair of the existing MIDI encoder without a sense of how much DIY effort can be pumped into a project. Get the MIDI board repaired if in any case, but don't stop there. There are encoders on the market that will do the keyboards, pedals, stops, and pistons with a bit of rewiring and soldering. You have a "blind" combination system now. That won't change because the stops aren't SAMs, but they will function pretty much as they do now.