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,
and OL-1, again after restoring.
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.
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.
And finally, have fun 🙂
For Heathkit OL-1, here is a block diagram of the schematic,
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