Forum Top Banner Ad

Collapse

Ebay Classic organs

Collapse

Announcement

Collapse
No announcement yet.

Early 1970s Allen with electrical short - what do I do?

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Early 1970s Allen with electrical short - what do I do?

    So, I just got this old Allen digital computer organ from the early 1970s. When it was given away, it was said to have a short in the electric and that seems to be true. Sometimes it doesn't work and sometimes it does. How can I catch it at the right time and how much should it cost to get this problem fixed?

  • #2
    Hi,

    How do you know it is a "short" that is the problem?

    A serious short will generally cause something to fry, or blow a fuse.

    I would say, the cost to fix it will exceed what the organ is worth.

    AV

    Comment


    • #3
      Alot of info missing here to do a drive by diagnosis. First off when the organ is on and then "shorts" is the power light still on? I'm wondering if there is a defective power switch. More information is needed like what is actually happening and when does it happen and does it "un-short" by itself and start working again. We're all ears :-)

      Comment


      • #4
        Originally posted by Hamman View Post
        Alot of info missing here to do a drive by diagnosis. First off when the organ is on and then "shorts" is the power light still on? I'm wondering if there is a defective power switch. More information is needed like what is actually happening and when does it happen and does it "un-short" by itself and start working again. We're all ears :-)
        Today when I was playing it, it suddenly stopped. I think one of the speakers is blown, as it makes a humming noise when the organ is working. The power switch was still in when the organ shorted out and it still looked like it was on. Apparently, it is "bipolar", where it goes through long periods of working and long periods of not working. I think it also has some stop problems as well.

        Comment


        • #5
          You could find a much better organ than this Allen. It sounds like it has had its days.

          James
          Baldwin Church Organ Model 48C
          Baldwin Spinet 58R
          Lowrey Spinet SCL
          Wurlitzer 4100A
          Crown Pump Organ by Geo. P. Bent, Chicago, Illinois


          Organs I hope to obtain in the future:

          Conn Tube Minuet or Caprice even a transistor Caprice with the color coded tabs
          Gulbransen H3 or G3, or V.
          Wurlitzer 44, 4410, 4420, ES Reed Models, 4300, 4500, Transistor Models

          Comment


          • #6
            A model number would be useful to help in diagnosing the problem.
            There are several power supplies in MOS organs in addition to the amplifiers.

            td
            Servicing electronic organs since 1969.

            Comment


            • #7
              Originally posted by tucsondave View Post
              A model number would be useful to help in diagnosing the problem.
              There are several power supplies in MOS organs in addition to the amplifiers.

              td
              It is a 30X-C, or System 300. I don't want to replace it, as it replaced a crappy organ.

              Comment


              • #8
                At this age, it is quite likely to be an amp or power supply problem. These are fairly inexpensive to repair, but require some skull sweat.
                I would normally discount the bad speaker theory but Allen was known for purchasing particularly short lived ( 10-15 years) speakers at one point. First look at the cone suspension - the bad ones get missing bits of surround. Second, with the power off, push the center in and out. Good smooth suspension and no scraping of windings on something (bumpy feel) there probably is no speaker problem. You can, with the wires disconnected, measure the speaker coil at about 7 ohms, on an 8 ohm speaker. If low some coil may be internally shorted. I don't imagine the transistion to 4 ohms speakers happened until the late seventies. You can test the speaker with a transistor radio when disconnected from the amp if you want to go that far. This test would get you to look at the speaker wire to the amp, which could be jumbled up by whoever removed the organ from the previous owner and sold it to you.
                The S100 amp is a conventional two supply push pull single output transistor model, op amp input, ltp next stage, upper and lower drivers with double diode and transistor bias control. There appears to be no protection relay (which is another troublesome parts after 5 years of exposure to air). The schematic has been on organ forum. Most likely symptom at this age, the power supply rails are dipping in voltage with the silence. You can test this theory with a fast DVM on the power supply capacitors. At this age, those rubber sealed wet parts are very suspect. Read the safety sticky thread before this work.
                Ittermittant Hum out of the amp could also be an open on the input. Allen was known for high quality assembly work, so I don't suspect bad solder joint, but a bad crimp on an input wire terminal or something could be opening up. Dirty tab contacts or loose wiring connections anywhere could cause this silence with hum symptom. Ittermittant hum could also be the power supply cap shorting out in the power amp. Electrolytic caps are the rubber sealed water filled (or dried up) usual suspects, not the plastic film or ceramic disk capacitors. To TusconDave's point, there are other power supplies that can go ittermittant too, same catagory of part is the root cause, although permanent silence can be a blown rectifier caused by a shorted e-cap somewhere on the load side.
                If this is all over your head, buy Thomas Floyd Electronic Devices the Electron Flow version which discusses meter use and power supply design in the transformer-rectifier-filter cap era. There is also some amp theory in there. More advanced is this thread about power amps: http://www.diyaudio.com/forums/solid...de-manual.html
                One determines the problem is in the power amp by taking an analog measuring device and proving the music comes in the input at all times when the failure occurs. Such devices are scopes, sound probes, analog voltmeters with a 2 VAC scale. DVM generally produce random numbers on music on the AC scale, although the Fluke 177 is supposed to read up to about 5 khz accurately. My Simpson 260-6XLPM produces useful results at the megahertz range, I don't know why people are so stuck on buying digital meters. digital is useful for checking plus and minus DC power supplies with one meter setting, but they miss a lot of transient shorts by being too slow, averaging the signal over about 4 seconds.
                this organ could be worth $3000 in my area if working, with all these seminaries and organ schools around here, so I see all the naysaying above as the complaints of people afraid of learning something new. An organ amp is a hifi amp is a tv amp is a radio amp. Buy them and throw them away every 5 years like the lords of commerce have dictated or learn to fix them and save sending that heavy metal to the dump for another day. Allens have been more like 25 year life products than consumer products, but with the replacement organs costing $$$$$ to $$$$$$, learning to repair the documented parts (like the power amp) could be rewarding. Not the digital bits, those are proprietary and after the MOS models usually secret, but this problem does not sound digital to me.
                One other quirk of MOS Allens, there is a volume dipping power resistor that is put in series with the speaker by a relay when the echo tab is activated. The variable tap on this resistor can be oxidized, as can the relay contact. both could use some contact cleaning with a file, not sandpaper or anything that leaves bits of insulating sand in the contact surface. An automotive points file is useful. This little chassis is in the back, the speaker wires from from the amp to it and then out to the speaker. Sound can get lost in it when it is old.
                Good luck and happy learning.
                Last edited by indianajo; 06-10-2015, 08:13 PM.
                city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

                Comment


                • #9
                  Originally posted by AllenMDS View Post
                  It is a 30X-C, or System 300. I don't want to replace it, as it replaced a crappy organ.
                  The power supplies are about the only parts that can be repaired in the field aside from cleaning connectors.
                  The main supply has -27 , +5, and -5 volt outputs. They should be measured for both proper DC output and no AC output.
                  It's unlikely that both amplifiers fail intermittently at the same time.

                  td
                  Servicing electronic organs since 1969.

                  Comment

                  Working...
                  X