Author Topic: Heathkit IO-12 recap and a question  (Read 5699 times)

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Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #75 on: May 18, 2021, 04:00:32 am »
I'm in Maryland, why?
 

Offline Quarlo Klobrigney

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Re: Heathkit IO-12 recap and a question
« Reply #76 on: May 18, 2021, 05:40:16 am »
Just wondering if you were anywhere near. Nope
Voltage does not flow, nor does it go.
“I do one thing at a time, I do it very well, and then I move on.”
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #77 on: May 18, 2021, 05:50:15 am »
Uuuuh, how is Portugal anywhere near the USA?  Do I need to buy a new map?
 

Offline floobydust

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Re: Heathkit IO-12 recap and a question
« Reply #78 on: May 18, 2021, 05:51:11 am »
V6a the only way I can see AC at the grid but not the cathode, would be C127 47uF (-) shorted to GND at the HOR. GAIN pot pin 1. The DC voltages are bang on for V6a. You checked for AC mains ripple at FF right, so the filter cap C133 20uF must be OK?
 

Offline Paul Moir

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Re: Heathkit IO-12 recap and a question
« Reply #79 on: May 18, 2021, 05:56:51 am »
Rickenbackerman:  Sorry about the pot, I don't know how I missed that.  I guess that's a rather dead horse at this stage.
I've been looking very closely at the pictures you posted for some time trying to find a problem, but I haven't seen it. 

Not relevant, but that 0.05uF Phase - capacitor floodbydust is on the bottom right hand side of the schematic, beneath the pilot light.  It looks like they're just picking up the filament voltage off V6 since it is a convenient spot.  It's kind of a silly thing.

The voltages match pretty well, at least the DC.  It took a while for pin 2 to drift down and a while for pin 3 to drift up while measuring, but they match your values.
For AC I couldn't get the cheap TRMS meter I have here to read properly due to the DC offset.  I had to resort to my (non TRMS) Fluke 8120A which read 1.3VAC on pin 2 and 1.1VAC on pin 3.  I confirmed their values with a 'scope so I don't think there's any funny business here.  I can bring my Fluke 175 or my EEVBlog 121GW(!) to see how they do if you like.
Dumb question:  both filaments are glowing right?  Sorry, I'm about out of ideas. 
Finally sharing my ugly IO-12:
« Last Edit: May 18, 2021, 06:08:17 am by Paul Moir »
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #80 on: May 18, 2021, 06:20:05 am »
flooby - tested FF for AC, saw none.  C133 is one third of the 20/20/20 CE can which is brand new.  Lifted a leg of C127 and tested it, it's fine.  Thought maybe I got bad one from the factory there, too, but it tests good.  And not shorted anywhere.

Paul - I LOVE your "ugly" IO-12 since yours actually works!  The DC voltages take a couple minutes to settle down here, too.  I SINCERELY appreciate it, but don't worry about testing any further, we all know what the problem is now - "something" is going on at pin 3.  I get ZERO ACV there no matter what.  I've looked at it from every angle and scratched my head for weeks.  For the hell of it I even reflowed the V6 heater joints even though the heaters there work fine...

edit: Paul - NOT a dumb question about both filaments glowing which is why I just reflowed those joints!  I wonder if I should I look closer at that, though?  I have never even looked close enough at a 12a*7 to see if you can tell if both sides are glowing?  I always just assumed if it was orange it's good to go?


edit #2: what if I desolder the wire from pin 2 of the horizontal gain pot and then recheck the ACV at V6 pin 3?  That would at least separate V6A and V6B.  I wonder if something on V6B is dragging down V6A?  Pin 7 is the V6B grid, though, so that doesn't make much sense, but it's an idea, and I'm about out of those, too.
« Last Edit: May 18, 2021, 06:33:41 am by Rickenbackerman »
 

Offline Paul Moir

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Re: Heathkit IO-12 recap and a question
« Reply #81 on: May 18, 2021, 07:05:41 am »
I was thinking something similar but rather C127 from the pot:  Floodbydust thinks something is shorting this to ground which would affect the AC but not the DC.  I know you measured this and did not find it so it would have to be a magical tin whisker or something like that.  Actually let me test that and confirm that's what happens.
Yeah, it sort of duplicates your readings.  The DC volts go up a bit (62 to 67) on pin 3 but it completely zeros out the AC component.


 

Offline Quarlo Klobrigney

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Re: Heathkit IO-12 recap and a question
« Reply #82 on: May 18, 2021, 06:19:38 pm »
Not only do I need sleep, I need to really sleep and not sleep post. :=\
Not only the wrong forum, but the wrong website. :palm:

Quote from: Rickenbackerman on Yesterday at 14:50:15
Uuuuh, how is Portugal anywhere near the USA?  Do I need to buy a new map?
Voltage does not flow, nor does it go.
“I do one thing at a time, I do it very well, and then I move on.”
 

Offline floobydust

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Re: Heathkit IO-12 recap and a question
« Reply #83 on: May 18, 2021, 06:26:40 pm »
I never mentioned that I cleaned the pots?  Jeez...  Yeah, I D5'd 'em weeks ago, they all needed it badly.

Checked all connections and components around V6A for the 17th time.  Reflowed a few more joints and scraped a little bit more nasty old flux off the bottom of the board between traces.  All looks good.

V6A DCV:
Pin 1 - 126V
Pin 2 - 12.7V
Pin 3 - 62.2V

V6A ACV with the horizontal selector set to "Line SW":
Pin 2 - 1.7V
Pin 3 - 0V

The horizontal gain pot is fine, I'm AM certain of that.  I tested it about three different ways by now.

edit: I also retentioned V6 socket pins 1-3 and hit all of the tube pins with a spritz of G5 gold (the hi-temp stuff).

Your measurements still do not make sense  :rant:
You say V6a pin 3 cathode 0VAC yet you have some horizontal sweep on the CRT which says that is not the case. What are you doing wrong here? Is there oxide on the points you are measuring, your DVM has beer spilt in it or what?
 

Offline Paul Moir

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Re: Heathkit IO-12 recap and a question
« Reply #84 on: May 18, 2021, 08:34:44 pm »
Hi Floodbydust,

The small trace collapsed to a point when we started using the "Line SW" input.  I suggested this for two reasons, one of which was to put a 60Hz sine into the circuit so we could measure the voltages with a multimeter.  I wasn't having much luck producing a repeatable measurement test for the sawtooth.  At the time I presumed that the higher frequency of the sawtooth was leaking through somehow.  I also presumed we would find the problem quickly.

I've been concerned that the "Line SW" was somehow leading us down the garden path and so have been checking a few concerns I had behind the scenes.  I don't think I have but doubt is the name of this game.
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #85 on: May 18, 2021, 09:47:41 pm »
I did say I had the Horizontal selector on "Line SW" when I took those measurements, and get zero trace width on "Line SW" as I rotate the Horizontal gain pot.   I only see hints of width up on the other settings (10, 100, 1000, etc) but I didn't check AC at V6 pin 3 when set on those...

My meter IS flaky, though!  Sometimes I have to rotate the switch back and forth a few times to get it to settle down.

I had an idea earlier today for another test to try - I'll report back later...
 

Offline floobydust

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Re: Heathkit IO-12 recap and a question
« Reply #86 on: May 18, 2021, 10:02:39 pm »
It looked like there's signal coming into a stage (V6a grid 1.7VAC), and nothing out (cathode 0VAC).  Either an open connection to V6a grid (at the tube) or a heater-cathode short, but the filament winding is supposed to be center-tap grounded and could not float up to 62.2VDC ... so the problem is likely voodoo.

For the sweep source, LINE SW is high impedance and lower amplitude than the sweep osc. due to the PHASE potentiometer, capacitive divider C41 etc. so FIL(B) might be really a too small signal and it's just hum pickup, so the 1.7VAC is a red herring. Many multimeters can't handle a large DC offset when measuring AC. Clipping at the A/D or just plain lie and give bogus values. Bad firmware as well. You have to know your test equipment so it doesn't lead you on a goose chase. Some multimeters can even get damaged because they auto-range down looking for AC yet DC is present, while the AC stage input cap gets charged up, which then discharges and kills the multimeter's front end when you next probe anything else. Might have to make an RC circuit prevent the drama. I think the ACV measurements are not working out as we expect.
 

Offline Paul Moir

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Re: Heathkit IO-12 recap and a question
« Reply #87 on: May 19, 2021, 05:05:39 am »
Hi Floodbydust,

If you look at the initial measurements I got Rickenbackerman to do on the other side of C126 and C127, it was to avoid the DC offsets.  They sort-of-suggest the measurements he made on pins 2 and 3 are possibly correct.

But the differences in impedance are something I wasn't thinking of.  I'll try loading down the stages at a couple places to see if I can get the results replicated.
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #88 on: May 19, 2021, 05:15:05 am »
Here is the test I wanted to perform - some questions still as to the horizontal gain pot being the issue - I checked it three different ways and was sure it was good, then today I thought "you know what, I AM sure of nothing" and thought of a simple way to totally get rid of it as a culprit - remove it entirely from the circuit.

Disconnected C127 and the wire going to V6 pin 7 from the pot, connected them together and then add in a 10K resistor to ground to simulate the pot resistance.  This simulates the pot being in the circuit and turned up all the way without the pot actually being in the circuit.  Not a very complicated test, no, but now we can be 110% sure that pot is good, and I feel better about that now at least.  Pic attached of my temporary wiring...  V6 removed just to take the picture, obviously...

Same result - dot on Line SW.  Hints of horizontal gain up on 10, 100, 1000, etc...  Want any more voltages checked while I have it hooked up like this or should I put it back the way it was?  If you guys think the DC offset messing with my meter at pin 3 - or elsewhere - I have tons of coupling caps and jumper leads here so I can put a cap in series with the positive probe?  Am totally comfortable poking around, like I said, I got nailed once and I know my limits. 
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #89 on: May 25, 2021, 04:34:12 am »
Anybody got any ideas?  I'm pretty much out of those...
 

Offline floobydust

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Re: Heathkit IO-12 recap and a question
« Reply #90 on: May 25, 2021, 07:25:12 pm »
I would backup and try something different. Strong assumptions (if wrong) can really make a mess when troubleshooting.
I thought we were trying to see if the sweep-amp V6 was doing its job, and the multimeter seemed to be lying about things. On ACV there is DC present at most nodes, it's a sawtooth, high impedances at the grids, so a digital multimeter can give misleading results. Or the probes are pooched or something else is not working.

I would forget about the H-sweep, who needs it anyway lol and see just how the Vertical section is doing.
Is it reasonable height when the scope probe is connected to the 1Vpp ref? Although all you'll get seems to be mostly a line, it's good enough to use for checking signal amplitude as we probe the H-sweep section...
I'm saying use the scope to probe itself, inside the horizontal section. Unless you have other test equipment. A common aspect between the two sections (V, H) is the SYNC portion, so I'm not sure where you want that switch. But poke around and try see (again) if V6 is amplifying anything. You just need ballpark ACV measurements as we are looking for where all the sweep signal gets lost - if that's the problem.
When the HV caps C36, C37 0.1uF 1,600V died, did they short and damage R71 470k 1W or the 1V2? Just checking because low HV can give weak V and H deflection. Don't have a beer and try measure it.
 

Offline james_s

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Re: Heathkit IO-12 recap and a question
« Reply #91 on: May 25, 2021, 07:32:40 pm »
I had a thought, are we sure the problem is with the H-sweep in the first place and not with the blanking? Does the trace look compressed or are the edges of it simply being cut off?
 

Offline floobydust

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Re: Heathkit IO-12 recap and a question
« Reply #92 on: May 25, 2021, 08:11:49 pm »
C124 measured 0.028uF but did not hear back if OP ran the scope with the lifted leg (disconnect one end of the part) to see what happened with the blanking disabled post #45
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #93 on: May 26, 2021, 05:04:05 am »
When the HV caps C36, C37 0.1uF 1,600V died, did they short and damage R71 470k 1W or the 1V2? Just checking because low HV can give weak V and H deflection.

C124 measured 0.028uF but did not hear back if OP ran the scope with the lifted leg (disconnect one end of the part) to see what happened with the blanking disabled post #45

Ok, I admit I must be getting frustrated and possibly leaving out critical info.  So, let me step back a few and give some more...   

BACK STORY!  When I shelved the 'scope, the horizontal amplifier worked fine.  It was the vertical amp giving me issues.  It would "freak out" every couple of minutes (screen would turn to a blur of mush (vertical amp) everywhere and if I'd flip the SYNC Selector back and forth it would stabilize...  for another minute or two.  Then freak out again.

Pulled said 'scope off the shelf (before recapping) and plugged it in.  No trace or even a hint.  Noticed the 1V2 wasn't lit, so ordered a couple used good ones and caps and then recapped the 'scope.  (C36 and C37 had puked their guts everywhere, and the cans didn't look much better).  Plugged in a "new" 1V2, was happy to see that I at least had a sign of a trace, and now four pages later on the EEVblog here we are...

I thought I tested R71 but let me test it again...  492K, so not THAT far off.  And the "new" 1V2 pegs the meter on my BK747B.

And I did run the scope with a leg of C124 disconnected, no change in horizontal deflection.  I thought I mentioned that but I looked back and realized I didn't say...

A little bit scared about using the 'scope to "probe itself" - I have Zero HV probes here, only a 1:1.  The vertical amp sure does seem to look like it's right on, now.  Connecting the 1V-PP gives me a nice controllable vertical line with the Horizontal selector on LINE, and barely a half inch wide "trace" on the other settings.

No other useful test gear here. 

Pic of scope with 1V-PP connected, ignore that the VERT input switch is on X1, I think pin 1 and 3 wires on that switch are swapped, been that way since I've owned it.  So X1 is X100 and X100 is X1.
 

Offline floobydust

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Re: Heathkit IO-12 recap and a question
« Reply #94 on: May 27, 2021, 07:51:55 pm »
This stuff is supposed to be fun, it's an adventure repairing vintage gear and keeps your skills sharp  :-/O
There are many ways to fix equipment - keep replacing parts or troubleshoot each stage to the component level, start the end, or the middle or the beginning stage.
I was looking at the three sections responsible for the H-sweep: Osc. V4/V5, H-amp V6, H-CRT driver V7 and we need to have some idea what stage is not working. Your DCV measurements seem to show everything is reasonable.
So one approach is start in the middle, see if the sweep amplifier has good output voltage, comparable to Paul's scope.

OK, no probe but no problem to poke around in the horizontal section as long as what you are using is touch-safe. Or just power it down and connect the test lead, then power on and measure, every time.
Can you fix the V/div switch wiring with R1, R2, R3 to avoid confusion. Everyone note this scope vertical section is only AC-coupled, so DC offsets do not get in the way.

I would do a measurement at the top leg of the Horiz-Gain pot R52, we need to know how many ACV is coming out of the sweep amp buffer V6A .
When you have the HOR/FREQ selector in LINE SW position, you are not even using the sweep oscillator. It's just a sine-wave 3Vpp FIL-B coming into the horizontal amp, so completely bypassing the sweep oscillator V4, V5. This leaves only V6 and V7 stages to measure.

Using the Vertical section, can you look at:
V6A output pin 3 or at the pot at R52. Should be around 3Vpp?
V6B pin 8 plate H-amp output. Should be around 30-60Vpp?
Biggies are V7 plates pin 1, pin 8 should have lots of voltage swing there but we don't seem to have it.

With blanking disabled, C124 leg lifted I would have expected to see a retrace line, the time when the beam zips back from right to left in readiness to do the next sweep.

If you're not wanting to make measurements, then carefully retest the all parts in the section - R260, R261, C230, R151, R254 etc. without assuming any of them are good.
« Last Edit: May 27, 2021, 07:54:35 pm by floobydust »
 

Offline Paul Moir

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Re: Heathkit IO-12 recap and a question
« Reply #95 on: May 29, 2021, 09:48:04 pm »
I don't want to interrupt this path since I think it is a good one, so this is directed to floodbydust:  If you're worried something is broken in the LINE-SW setting, I was going to propose connecting 1Vpp to the horizontal input and using the sweep selector on EXT. INPUT.  It gives us a lower impedance source, though that shouldn't matter. 
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #96 on: June 04, 2021, 04:41:14 am »
Ok I'm back after another relaxing week at the beach away from this confounded scope that's making me pull my hair out.

Just kidding! Like flooby said this stuff is supposed to be fun.  Step away if you get irritated or confused.  Rethink things.  Double check previous work.

Didn't have much time tonight to poke around but I'd like to fix the 1X/10X/100X vertical V/Div selector switch first if we're going to use the scope to probe itself so nobody get confused.  Good idea and I like it, too.

Paul can you flip yours upside down on the bench and take a looksee if you still have the cover off and it's not too much of a pain?  I think I need to swap wires 1 and 3 on the switch (counting lugs 1, 2, 3, 4 up from the bottom of my picture)?  I'm seeing conflicting things on the various skits I have printed out here, not all things are labeled, etc... and figured it'd be easier to just ask you.  And those wires are solid core, not too easy to get to, wrapped around the lugs and don't look like much fun to swap if that's not it.  Pretty sure it is, though.

« Last Edit: June 04, 2021, 04:53:14 am by Rickenbackerman »
 

Offline Rickenbackerman

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Re: Heathkit IO-12 recap and a question
« Reply #97 on: June 04, 2021, 05:21:25 am »
One last quick test before I hit the sack...

V6 Pin 2 to vertical input.  Sync selector to -INT, Horizontal selector to Line SW, I still have the horizontal gain pot bypassed so that's maxed out.  Pic below of this test.

Same settings - V6 Pin 3 to vertical input only gives me a dot!  So V6A is clearly not working.  Why???  I don't get it...  At least we've proved what Paul said back in post #62.  Although he already knew it!  Ha!
 

Offline MathWizard

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Re: Heathkit IO-12 recap and a question
« Reply #98 on: June 04, 2021, 04:12:49 pm »
The schematic is quite similar to an old scope I have. It's transformer is fried and I never got around to getting a suitable replacement. Maybe this year when i have some extra money.
 

Offline Paul Moir

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Re: Heathkit IO-12 recap and a question
« Reply #99 on: June 04, 2021, 06:36:05 pm »
No problem at all.  It's good to take breaks from this kind of work when you can, especially if you're not having fun.  I've got email notifications on so it's not any burden.

Unfortunately it looks like another mystery, since the wiring looks correct.  And the labels match so that's not it.  I think you're trimmers are installed the same way around, with the trimmer with the white plastic cylinder beneath the adjustment screw towards the front & bottom of the 'scope. 

And another horrendous shot from my 'scope.  If I remember right, R1 had drifted really badly.  Also if I remember right, the trimmers took some serious exercising to get working cleanly so there might be an open there.

EDIT:  Oh, I think we just have a terminology problem here.  They work identical - X1 really means divide-by-1 while X100 means divide-by-100.  Not multiply-by.  So a 1Vpp signal fed to the vertical on my 'scope is biggest on X1, smaller on X10 and tiny on X100.

I also replicated the V6 pin 2 setup and I'm getting a diagonal line, due to the functional horizontal amplifier.  I get a higher amplitude (10% on the vernier is about the same as Rickenbackerman's 30%) and no opening into a circle, except briefly during warmup.  I'll try a few things later tonight.

« Last Edit: June 04, 2021, 07:02:02 pm by Paul Moir »
 


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