Heathkit IO-4540

I’ve run across several requests in electronics forums for the schematic of this very old Heathkit IO-4540 5MHz Single-trace Oscilloscope.  The schematic in the Heathkit manual is a large foldout and is difficult to scan.  These are photographs of the four quadrants, and are better than nothing.

All four schematic photos in a single zip file (3.5Mb)

Also, selected pages from the “Illustration Booklet”:

Illustration Booklet Figures in PDF file (1.4Mb)

13 Responses to Heathkit IO-4540

  1. Bill says:

    Thank you.

  2. Robert Lyon says:

    Hi, I recently picked one of these up, and am trying to calibrate it.
    I got as far as the trigger circuit, but then the manual refers to an “Illustration booklet”
    to make various adjustments.
    Without the illustrations, I’m stuck!

    Any Ideas?

    Thanks,

    Robert

  3. Bruce says:

    I have a Heathkit IO-4540 scope and the vertical trace has disapeared, I have the horizontal trace and it works fine. How do I get the verticle trace back.?
    Thank You
    Bruce

    • modemhead says:

      I assume you mean that you have a flat line and no vertical deflection. Set the Volts/Div appropriately, set the coupling switch to AC or DC, and input a signal. The 1Vpp available from the front panel will do. If you still get a flat line, then there must be a fault in the vertical amp.

  4. Hunter says:

    Does anyone know what to adjust for the dc balance and plate volts on the horizontal board? The variable resistors broke and I was going to replace but have no idea what they need to set at or what to do for adjusting them.

    • modemhead says:

      I do still have the manual for this scope (Heathkit IO-4540). I’m out-of-town at the moment but when I get back I’ll see if I can dig out the horizontal board adjustment procedure.

      • Hunter says:

        I ordered another one but it broke in the mail too. Became a parts one and I got the first one working. The calibration is so far off. I pretty much just need the full manual to calibrate it. At least it works now even if the case is completely destroyed.

  5. Richard Montel says:

    Link to IO4540 schematic photos doesn’t seem to work.

  6. Josh J says:

    Dumb question – forgive me. My son is trying to create a spaceship control panel so we bought one of those at a swap meet. I get a horizontal line which is great. But now I want to create some kind of wave form. What would you suggest?

    • modemhead says:

      First, be cautious of the inside of the scope, there are some dangerous voltages on exposed connectors.

      If the scope actually works, I can think of several options:

      1. Find about 1 foot of scrap wire, strip one end and stick it in the center of the “INPUT” BNC connector. There will probably be enough electrical noise in the enviroment to make an interesting waveform. Turn the “VOLTS/CM” knob clockwise for max sensitivity. You can also touch the end of the wire and get a bigger signal.
      2. Connect the wire from above to the “1V (P-P)” banana jack for a reasonably clean sine wave display.
      3. Find a speaker from an old radio. Connect it to the BNC input. (Use 2 wires, one to the BNC center, one to the outer shell.) The speaker will act like a microphone if you speak into it, and the scope will display the signal.

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