Restoring Heathkit Vintage Oscilloscopes (IO-17, OL-1)

If you are reading this and don’t know what Heathkit was, I would suggest you explore more. They made a generation of genius folks I feel. DIY to a High-Tech level. Its sad that I have to write “Heathkit was” I may be mad, but I love them. I really don’t know why. Now, we often come across these scopes, of all models, and I find them very interesting. They are a walk in the park compared to a Tektronix . But they do command a whole lot respect for what they did to make Information Technology and Electronics what it is today. So with all due respect to the great men and woman in Heathkit and hundreds or thousands of souls with craftsmanship who brought Heath-kits to make their own test instruments. I have restored  two of the Heath Scopes, OL-1 -1950s era and IO-17, of a bit later years. They  both are design marvels in terms of simplicity and cost effectiveness plus being DIY. Just sharing the basic steps in case you are trying to restore one of these. RULE#1 – DO NOT POWER THEM ON. HOW-MUCH EVER TEMPTED YOU ARE, NEVER POWER THEM ON UNTIL YOU ARE SURE ITS READY TO TAKE IT. ELSE IT WILL DESTROY THE UNIT BEYOND REPAIR. Like I always do, I will not cover basics, or stuff what is already written all over the blogs and videos and documents, to avoid duplication. I will just point the quick tips, tricks, to help you get one of these guys back to life. Here is an IO-17 after restoring it, IMG_1710 copy and OL-1, again after restoring. IMG_1552 Note: The Gain means Volt/Div. Its a POT, not a switch. These instruments are NOT for measurements, only to see the signal. When you get one of these, they may not be in the best state of their life. Here are some examples (real) when I grabbed them. Covered in mud, dirty panel/Knobs. Broken connectors. So first step is to open and clean, anything and everything, I dont work on any gear unless they are clean. so always I clean the gear before working on them, end to end, from PCB to components, to knobs to case. So lets open these toys up and start cleaning them. Here is how dirty they are typically, unless the owner took care of them, which is rare. All pictures are from OL-1 And  next step is to clean. Brush, Alcohol to wipe all critical parts, and wash the knobs, air-compressor to flush the dust out. Take out CRT for inspection and cleaning. You can find both IO-17 and OL-1 undergoing through the process. You can also see the Can Electrolytic Cap. I removed it to clean the base. I do remove the CRT and clean too. Now third phase, Fix. Basic process is 1. Recap or replace all capacitors- Replace ALL electrolytic, Paper, and WAX. You can leave the disc (Ceramic), unless you see physical damage. Mica ones – Test with Leak Tester, or best – Replace ALL NOTE: HV To the tube is -ve. if you are ever replacing the main HV cap with a polarized one, do remember this, else it can fry the 1V2 HV rectifier tube in OL-1. Screen Shot 2018-02-12 at 10.56.04 PM 2. Tubes – Test if you have a Tube Tester. Else, physically verify if any Tube is leaky (White substance/cloudy inside, check my Tektronix Post for sample picture). If not anything, I would suggest check tubes for shorts between elements with multi-meter. Typically these instruments have less than 15 Tubes in them, so easy, unlike a Tektronix monster. Basically any tube should NOT show continuity between any elements (cathode/Anode/Grids) and between any element to Heater (unless its a directly heated tube, where cathode is Heater). Heater should show continuity between its pins. 3. Resistors – Check all of them. Could be open ones. Pots – Clean with Proper Electric cleaner, NOT WD-40 or anything similar !! . Use proper cleaning products for PoTs. Google is your friend. Note: If your POTS for intensity/focus etc are not clean, your trace may be thicker/wider than it should be 4.Wiring – Verify with schematic. This is not a factory made instrument, the person assembled it may have made mistakes, or would have exposed terminals. I usually replace cables or rewire entire unit, Heat shrink connections and provide plastic shielding for connections close to Cabinet/Cover/Metal Parts of the cabinet. 5. Switches – Lubricate and clean. Again do not use wheel bearing grease and WD-40. remember, these are sensitive parts, do not use any harsh lubricants or cleaning agents. again Google is your friend as I don’t want to recommend any products. Important : DO NOT USE PETROLEUM BASED PRODUCTS. Do not troubleshoot any issues without cleaning switches as most contacts will be bad and that will be causing trouble. 6.Clean POTs. Use proper contact cleaner (electrical), no harsh cleaning agents. 7. This is again my personal choice – I do heat shrink all connections. Here it is in pictures You can see the vintage HV Caps with Ceramic insulated Connecting Terminals and the new Kemet 1200v replacements. Now once you are happy with all, time to power up.

Safety warning :

These instruments contain deadly voltages, powered from a transformer. They can supply sufficient current to kill you. do not attempt to repair or open any of these if you are not well trained/qualified to. There are better ways to die.

Do not poke around with cheap multi meters or probes, as typical voltages can reach 400v+ DC.

CAUTION: Front panel intensity/focus control POTS carry High voltages up to 600-1000v !!! BE CAREFUL !!!

Use a Variac, and slowly power them up, monitor current. Start at 20v, wait for few minutes,  and then go 40v, and then 60v input AC. You should see almost all tube filaments glowing at 60v. 1v2 filament will not glow. its just 1V. Keep the unit to warm up with half input voltage for couple of minutes. Check all secondary voltages and ensure they are ~ 1/2 of expected, both AC as well as rectified and filtered DC.  Check for overheating components. Once satisfied, you can go full line voltage to 115v and ideally you should see the trace, adjust V and H pos as well as intensity to get trace. Typically they do come to life unless any tube is bad, in terms of Gm, which I guess is rare. Here is how it looks when they come to life. NOTE: The first OL-1 with thick trace is when the intensity control POT is dirty. you can see it thin once I cleaned the intensity and focus PoT. Also on OL-1,   I replaced almost all wiring, remember to use 1500V cables, as the lines running to Intensity and focus controls carry close to 1000V. IMG_1544 2 And finally, have fun 🙂 For Heathkit OL-1, here is a block diagram of the schematic, OL1_Diagram

Heathkit IO-10 Schematic, Capacitor assembly drawing By  Chris Jenerick (Vons Garage)

Shared with permission, All credits to Chris and thanks for allowing me to share this.

Schematic (fixed the typo in grid voltage) – Click Here to download the original pdf

Screen Shot 2021-05-07 at 8.01.02 AM

Capacitor Wiring in color – Click to Here to download the original pdf

Screen Shot 2021-05-07 at 8.00.45 AM

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15 thoughts on “Restoring Heathkit Vintage Oscilloscopes (IO-17, OL-1)

  1. Hi,
    It’s great to see a good old electronic equipment being put back to life. I really love the vintage tube electronic stuffs. Unfortunately for me I live in the other side of the world where these things are quite hard to come by. So, usually have to import these stuffs from the US or Europe.
    I recently scored a Heathkit IO-10. It did power ON right out of box. Immediately recapped the equipment and things seemed to work fine. Tried an audio signal on the vertical input and got a waveform on the CRT. But while connected to the Horizontal input, it’s only a straight line. No, waveform on horizontal inputs like on the vertical inputs. I’ve only worked on Analog oscilloscopes that have 2 channels from the beginning. So, pardon if I’m wrong. Am I missing something here or is it the way it’s supported to work? Or is the horizontal input section not working? Most of the youtube videos and online blogs about vintage oscilloscopes show the inputs with connections made only on the vertical inputs.



    1. hey Rahul, I can understand the pain of sourcing components there, as I’ve been through that. I am not sure if I understand your question correctly, but H-Input is supposed to provide sweep, so it will only trace a line across the as you see. H Input is used in case you want to do X/Y plotting or want to have a different time base than available on the scope. On V- You see a waveform because the internal time base is proving the X-Sweep, where as when you insert a External H, its just replacing the internal time base. The signal you want to view against the H is still expected on the Vertical. – Quick note – Never power on vintage gear, without checking the Internals and caps, as it can burn things down, there could be dead leaking caps or shorted tubes or broken wiring insulation. General rule is to cut the power cord as soon as you receive it so that you are not tempted to power it on until its fully restored.


      1. Yeah, I absolutely agree with you. The funny part is the equipment or spare parts like a tube might just cost from $2 to $60, but the import and shipping charges easily reach or exceed $100. So, whenever I buy I make sure I get only a working unit or one that can be easily fixed.

        Thank for explaining it in an easy manner. Now my doubts are cleared! :).

        Yeah, I read on multiple websites including yours and on Mr Carlson’s youtube channel that powering on these vintage items without varian and current limiting is bad(especially those electrolytic caps). In my case the only reason I power On was because the ebay seller had some picture of signal traces and it was powered for like 15 mins he said. I wouldn’t risk powering ON and damaging it. Apart from tubes rest of the parts seems to be manageable to find.


  2. Thank you for sharing those links. I’ll definitely check them out. I have one question regarding paper & wax capacitor replacement. when replacing with metallized polypropylene caps I read that it is important to find the lead that is connected to the outer end of the foil. How much would the performance an equipment be affected if we don’t follow this?


    1. Its basically for Shielding from Noise/Interference. Easy way to understand is to compare it with Co-Ax Cable, where the outer Woven conductor is shield and grounded to give the inner conductor Shielding from Noise. In Film Caps, you keep outside foil for ground – on filter applications- and for coupling applications (audio Amp) you use the outer foil for output side of one stage and inner foils for input of next stage.


  3. Hello,I have read all Your recommendations and carefully studied the photos,thank You for such a detailed presentation of the materials. They helped me a lot in repairing the American IO-12 oscilloscope.I got it as a gift ,a friend brought it from Berlin in 2005.All this time it has been standing in my warm pantry at home and only recently decided to turn it on to pass it to my son.But when turned on, instead of the beam, it began to show a point on the tube screen.For three weeks I searched for an error and found a dried-up tubular capacitor/C127-40,0 mkf x160 volts and a faulty horizontal sweep regulator R -220 kom/. After replacing these elements,everything was restored, the beam and the oscilloscope scan began to function.All lamps work,the 1V2 кenotron outputs 1600 volts. The brightness of the kinescope tube is good,the focus is there. I can send You photos and videos on the oscilloscope for info.I have two professions-an electronic engineer and an international journalist.I’m from Leningrad-Petersburg, working in Europe.I have been doing stereo photo and video shooting since 1965.Thank you again for your material.All the best to you and good luck. Mr. Pavlov.


  4. Good Morning. I have restored a Heathkit IO-10 and am wondering if there is a possibility of a typo on the schematic. During checkout after the recap all the voltages are within 10% with the single exception of Pin 2 on V4A. Schematic states -62 volts but measured is -6.2 volts. If I was smarter I guess I could figure out what would make sense. If you have the time to look I would appreciate it.
    BTW; I completely redrew the schematic electronically and would be pleased if I could provide you a copy for your records.


    1. Hey Chris, yes, looks like a typo. That is the grid of 12AU7 triode, a -62V there will drive that tube to cut off since the cathode is @ 3.2V . If you look at the schematic, the resistor divider of 1M/100K (R22/25) should drop the -75V supply to ~ -7.5 DC for grid bias. With additional AC coupling from the previous stage, it can go a bit high. So yes it is -6.2V, not -62V.


      1. Thanks for the review, evaluation, and reply! Don’t spoil me. A brilliant engineer an email away!

        Again, thanks and here is a PDF conversion of the IO-10 schematic I redrew using Paint.Net which is a lot of fun to fool with. And now, thanks to you, it’s even correct.

        I hope it makes it thru and looks OK on your end.



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