Lowrey MX1 organ

[tuathal]

Hi to all the organ heads out there,

My Dad picked up a MX1 organ a year back at an auction, it was sold not working though the owner said it was working up untill they moved it to another room in there house, whether thats true or not i dont know.

anyway having studied electronic enginerring he was hoping i would be able to fix it for him. I opened it up today and there is acres of analogue and digital circuitry inside,

when the organ is swithced on, the digital display doesnt turn on and there is no response to key press or bass pedals but the speaker/amp and all the analogue stuff seems to work.there doesnt seem to be any fuses blown or burnt out components from my quick look at it. ive got a feeling its probabaly a problem with the cpu or some part of the digital circuitry.

if anyone has experience servicing these organs and has any suggestions theyd be very welcome. if i cant get any joy in getting it working again ill probably canabilise it, thought hat would be a shame because its such a great organ.

Thanks in advance

tuathal

[grahamprie]

Hi Tauthal,

I used to service Lowreys, but I moved over onto computers befre the MX-1 range was launched. If as you describe, so much of the instrument isn't working, it's probably a power supply fault - or a connector which came loose during the move... Without a schematic and some idea of what the bits look like you'll take forever trying to locate the problem - it's a shame I'm in England, or I'd have offered to have a look at it.

There's usually a large metal chassis which houses the power circuits and the amplifiers - look at where the mains cable goes... It's often used as the mounting for the volume pedal too.

If you look inside it ( unplug the mains first ) you'll probably find a set of identical circuit-boards - one per amplifier - and you should be able to feed an external signal into these through a series capacitor to check them out.

If the audio section is OK, you're down to checking all the low voltage stuff - and you'll need to do that that with the power back on - you can't touch anything dangerous if you put the amp chassis back first...

In this case, the problem is most likely just a loss of power, so you'll need a DVM. The power wiring is usually thicker than the rest, so ground the -ve input of the meter to the power chassis and poke around with the other prod to see where there is any voltage on the wiring to each section of the instrument. You may need to push your probe inside the mouldings of some of the connectors to get a contact.

Set the DVM for DC and 20 or 200 Volts and you should see something. Work backwards towards the power chassis.

Parts are still fairly easy to get - deciding what you need is the problem...

Happy hunting,

Graham

[gschneider]

I maintain an mx-1 for a relative... I need to replace IC 25 on board 15 but I can't cross reference the part and the service manual does not list it's origin. If you decided to canabalize yours I'd be interested in purchasing the IC from you.

[grahamprie]

Hi gshneider,

can you tell me what the part number is? A brief decription of the IC's function might help too... A lot of these parts are common across a whole range of the models, so I may be able to identify it for you. They were made for Lowrey by a number of suppliers, but were never available on the open market till the models were discontinued.

I still have a few oddments in stock from 1976... who knows?

All the best,

Graham

[gschneider]

Hi, the chip is made by Synertek and is described only as an SIC (serial interface controller). the lowery part number is
920-030708-000 This number is stamped on the chip which makes me think it was made for Lowery. there is also a date code on the chip 8332 which I'm told means the 32nd week of 1983. It's a 40 pin DIP. Any info would be appreciated....

There appear to only be two custom chips used in the whole thing... the SIC and PIC (paralell interface controller) (and of course the bank of PROMS... ) If anyone else happens to be parting one of these units out, I guess I should make an offer....

Greg

[grahamprie]

Hi gschneider,

It appears that Synertek operated from 1973 to 1985 as a custom chip fabriction house, making mostly pre-programmed ROM chips and a few speciality parts which were compatible with the Rockwell 6502 CPU family, which they also made under license.

It's possible that one of the perpheral interface chips for that processor family is the one you need, but without comparing the functions pin by pin between the schematic and a data manual it's a bit of a hopeless case.

The peripheral interface parts were numbered in a sequence like 6521, 6545, 6551, etc.

From memory, the serial interfaces had only 28 pins, so this may be something I've never seen.

Synertek were taken over in 1985 by Honywell, and the manufacturing facilities were turned over to Honywells industrial control systems - also based on the 6502 CPU at that time.

I'm afraid I've no idea what happened to any surplus stock - if there was any...

The only good thing is that if this board has a 6502 CPU, all the firmware will be in ROM so it would be possible to reverse engineer the functions if you had the knowledge and the time - I've done it before, and it's not pleasant, so the better option is to look for a scrapper and swap the parts.

Good luck, Graham

[LesE]

The Lowrey MX-1 organ donated to the village hall I help run has suddenly stopped. The lights all come on but there's no sound. Can anyone advise on the best way to investigate the problem or suggest an easy fix?

[tuathal]

Hi Grahamprie,

Thanks for the reply!

Finally got around to do a small bit of testing on the organ.
The amp/speaker side of things is working ok, i applied a signal to the audio ip and it amplified it fine.

I also did a quick voltage check on one of the power boards, i got the correct voltage readings, 24V, +-15V etc. Ive got a feeling its something wrong on the digital side of things, (which dosent narrow it down much i know).

Do you have any suggestions as to the best way to determine where the fault lies or is it just a case of testing the voltages on all the ics and taking it from there?

btw the organ was manufactured in 1980/1981

Cheers

Tuathal

[grahamprie]

Hi LesE and Tauthal,

It sounds as though you've both got similar problems, and I'm afraid that the only way to diagnose it further is to check all the power supplies from source to destination. Obviously it would help if you have the circuit to follow - but this type of fault is generally all or nothing...

On the other hand, if all the power is OK, it's likely that one of the digital chips has failed, and then the problem is proving which one, and getting a replacement.

I'm afraid you're probably on your own from here on...

Good luch,

Graham