Heathkit IO-12 recap and a question

[Rickenbackerman]

I know but the goo leaking out everywhere made me want to just shotgun all the caps...

Does this mean anything to you?  I recreated the "squashed on the left" look.

edit:  I printed out the skit you posted earlier, maybe I'm just using the wrong darn one.  I thought they were all "pretty much the same" and I just realized the one I'm looking at doesn't even have a "CC" supply.  I'm gassed, maybe back at it tomorrow night...

[Quarlo Klobrigney]

Still waiting on those voltages. Come back when you're charged back up.

[Rickenbackerman]

Okay fellers, I got some fresh eyes on this tonight...

I printed out Quarlo's skit (thanks man!) since it shows a 12BH7 as V3 which is what's in my scope.  flooby yours shows a 12BY7 instead...  I've had this thing for ages so I'm almost sure nobody's ever been inside since it was built.  Quarlo's skit is quite a bit different than the 0-12 one I was using before and has a lot more pin voltage data on it.  Sorry for my "psychic hotline" moment the other night!

Anyway, VOLTAGES!  Get your fresh hot voltages here!

Measured first, then the skit value.  My line voltage here is a pretty stable 120V BTW...

Power supply:
AA 377/370
BB 347/340
CC 140/135
DD 110/100
EE 120/115
FF 125/120
GG 110/105

Toobz:

V4:
1  93/90
2  19/15
5  0.2/1
6  -0.7/1
7  1.8/2

V5:
1  106/105
2  92/90
3  98/90
6  77/45 (!)
7  -2.4/-0.5
8  0/0

V6:
1  125/120
2  12.5/12
3  62/56
6  72/70
7  0/0
8  2.1/2.2

V7:
1  241/230
2  79/75
3  86/80
6  279/230 (!)
7  38/35
8  86/80

Some have changed since I took measurements last night, could have been psychic nazi probe operator error though.  The two I put exclamation points after jump out to me.

Guess I should check R144 feeding pin 6 of V5 first.  Then, not sure why the voltages on pin 1 and pin 6 on V7 are so different when I already checked both of those 33K 1 watters and they both read 35K?

I'll be on here for another hour or so then leaving town tomorrow for about a week...

[Quarlo Klobrigney]

Unless you have access on the road, everything on V4-V7 looks good except pin 6 of V5.
That wouldn't effect the horizontal sweep width.
It does note that C124 may be leaking as the cathode of the CRT is at a negative potential.
Did you change the 1KV caps, and with what?

[Paul Moir]

I have my IO-12 on the bench with the cover off at the moment.  Let me know if you want anything measured.

(I'll turn notifications for this thread on.)

I had replaced the GG ballast resistor (1.5K) because it had drifted.  If I remember right, I was getting a narrow trace as well.  But that may be a false memory.  It's running 106V right now, and I think your GG looks good so probably not that. 
My V5 pin 6 is at 50.5V.  But that's the blanker so that seems unlikely.  C124 is the big original ceramic hiding behind V10 in Quarlo's picture and seems like an unlikely candidate for being leaky.  It seems like something funny is going on with V5.

The only other ones I found that had drifted too badly were R182 on the V10 grid (bleed resistor) and the power resistors around V3 (2.7K x 2, 1.2K)
V7 1 & 6 have an awful lot to do with the exact setting of your horizontal position pot.  If I adjust mine so the dot is about halfway between the edge and the centre of the screen, I get 279V on one and 241V on the other. 

[Quarlo Klobrigney]

What picture?

[Paul Moir]

Sorry, Rickenbacherman's.  The picture with V10 in the centre...

[floobydust]

I think we are as far as we can go with only DCV measurements 
Problem could only be a low value coupling capacitor e.g. C126 0.25uF 400V, C127 40uF 150V, C128 0.1uF 200V, C230 0.1uF 200V that you need to look at the signals with a scope, or test each part.
Paul Moir can you can look (with a scope) at the output of the sweep oscillator, for amplitude so we can know if it's weak here or not.  Maybe V5A cathode or V6B plate. You might be able to measure it with a RMS multimeter (using an extra coupling cap to get rid of DC) like at C126 or V6A grid.

There's a chance there is nothing wrong with the H-amp and H-deflection or sweep oscillator. Instead, it could be the blanking malfunctioning. The CRT-beam being enabled for too short a portion of the sweep ramp. It's sweeping full H width but beam current only on for the inch, so it looks like a squished display, only a snippet is lit. Just a possibility.
V5B the grid bias is formed by space-charge and a very high impedance node with 22MEG resistor R142, so measuring with a 10MEG resistance multimeter there, the value will be thrown off. I think V5B is pulsed off? only for the retrace (blanked) portion of the inverted sawtooth it sees. So I would also check:
C116 100pF, C124 0.02uF 1,600V, R142 22MEG.

There might be a way to disable blanking, lift a leg on HV cap C124 or R144 etc and see what the screen looks like.

[Quarlo Klobrigney]

I think I already mentioned the capacitor C124 from the CRT in the blanking circuit. We will have to wait until he returns for the answer.

[Rickenbackerman]

Posting from the beach trying to digest all that you guys said, and thanks for the help!

Quarlo you asked about the "two 1kV caps" - C34/C37?  I got a couple 0.1/1600 film caps from mouser.  Not sure what brand but I can find out.  The original ones were literally leaking goo out everywhere.

I'll be home tomorrow night but I might not get back to it for another day or two.  Sounds like C124 is first to test.  I don't have an ESR meter but I have a decent DVM (which can measure capacitance) and a heathkit cap checker which I redid and works well.

Funny how I shelved the thing due to vertical issues and now the horizontal amp is the issue. The "squashed on the left" trace pic isn't a dead giveaway to anybody?  I thought it would be.

[floobydust]

We don't know what signal you are putting into the scope and what the sweep speed is. Is it supposed to be displaying a single sine-wave cycle?
If you measure the sweep oscillator frequency (e.g. with DMM) and set it to say 1kHz and the vertical has a 1kHz sine-wave coming in, that would tell more about a non-linearity or squished sweep ramp. Or maybe try it with the 1Vpp reference and line trigger (all mains frequency).

[Rickenbackerman]

Sorry flooby, I should have said that it was just a simple sine wave...  I forget what frequency...  Anyway, got home tonight and played around for a little bit.

FYI it should be noted that ALL of the electrolytics and ALL of the black tubular film caps have been swapped out.  The only original caps remaining are the ceramics.  In case that wasn't clear.  Not that those don't ever go bad...

I measured (in-circuit) a few things you guys noted I should check:
C124 - 0.028uF but like I said I don't have an ESR meter so I dunno if it's leaky or not.
R142 - 33M - a little high versus 22M, no?  (my DVM has a 2000M setting)
C116 - seems like right around 100pF but my meter was jumping around on that one.

I hooked up the IV P-P to the vertical input and played around with it - I've never even tried that before.  I could NOT get a decent looking sine wave at any setting, and I noticed that playing with the frequency vernier wants to make the trace either jump off toward the left or disappear completely.  It definitely moves it around horizontally though and it affects the intensity as well.  And I still get the "squashed on the left" look at certain settings.

When you guys talk about "blanking" and "sweep oscillator", I'm in over my head.  If you tell me exactly what to measure to try next, though, I'm all ears.

edit - Quarlo - for C34/C37 I used these:
https://www.mouser.com/ProductDetail/75-MKP1839410134HQ

[Quarlo Klobrigney]

Expensive little buggers! "For C34/C37 I used these:"
For C124 - 0.028 µF (or 28 nF) take it out of circuit. Discharge it and use your DMM on the highest resistance range to test it. It should charge, then go infinite. Flip it around a few times and try it again. If it doesn't go infinite or has a resistive reading that stays, it's leaky.

I use the 630V yellow polyester or whatever they are made of today. 2 in series is plenty to replace those 1.2KV caps. Of course, you have to double the capacity in series .056 µF (56 nF). At 50 cents apiece they are affordable. https://images-na.ssl-images-amazon.com/images/I/41gxqCXq3UL._AC_SX425_.jpg

"Dioda Gona Wildaaa" has a video on the sweep 07:33 and and blanking at 11:00. Starting here, https://youtu.be/TPX9BMDK4w8?t=453 he explains the basic theory with his cat assistant.

That was the quickest version I could come up with before bedtime.

For the out of range DMM resistor, you could always measure it in parallel with a known resistance with an online parallel resistor calculator. Use the known resistor that fits in the range of your DMM (2.2 MΩ for example) for the first value and substitute the printed value of the unmeasurable resistor. Now calculate the parallel resistance. Compare this to the example value and unreadable resistor in parallel.
That will give you the differential tolerance.

For example should take the 2.2 MΩ measured, put it in parallel with the unknown resistor (say it is 33 MΩ) the result would be = 2.0625 MΩ proving that the unknown resistor is not equal to 22 MΩ like in the next equation.

It should, for the 2.2 MΩ measured and the 22 MΩ required in parallel = 2 MΩ.

Just run a few values that you can parallel, through the calculator to find out.

[Rickenbackerman]

I will check C124 doing exactly what you said to do.  And I will watch that video.

But I think you misunderstood - my DVM can read up to 2000 MΩ (not sure accurate it is on that setting though!).  R142 reads 33MΩ vs 22MΩ.  I'm an engineer, so I prefer to not have to do math if I can help it!   

[Paul Moir]

Sorry I'm so late in replying.  I keep forgetting my digital 'scope so we'll have to live with my old 465, so unless you really want pictures I'll do this verbally.

On Cathode of V5A we're seeing a nice sawtooth like you would expect; it gets a little rounded on the lowest range (10 CPS) but it has a nice sharp rise.  Vpp is about 8V with the vernier at 10% and goes to 14V with the vernier at 90%
V6A plate is practically DC.  1Vpp uuuu shaped wave at the lowest sweeps and diminishing as the sweep rate increases.

I've been trying to work out a system for measuring this amplitude but haven't been successful yet.  I couldn't get anywhere with AC even with a good blocking capacitance on a TRMS meter, I'm trying to get a good rectification signal so we can use (a reliable) DCV with a pretty simple setup.  I'll keep working on it.

Can I suggest a simple test?  If Rickenbackerman sets his Horizontal Selector to "Line SW" (60Hz Sine wave) he should get a line that can be expanded past the extents of the CRT.  This takes out V4, V5, and their associated circuitry as culprits. 

Quarlo:  are you thinking the blanker is overblanking the sweep?  If so I tried lifting a leg on C124 disables the blank just like you would expect without any obvious side effects.

[Rickenbackerman]

Paul, no worries - I was at the beach for a week!

Horizontal Selector to "Line SW" - check - with no input I get a single dot with the horizontal gain on all settings.  I hooked up the 1Vpp and I get a vertical line with plenty of vertical gain.  And here's a weird one - if I move the horizontal position pot back and forth real fast I can get a somewhat decent looking sine wave the full screen width, although still smashed on the left.  It only does that when I move it, if I stop it goes back to the vertical line...

Lift a leg on C124?

[Quarlo Klobrigney]

I was tired when I read the 33M - DMM part. In that case, it's out of tolerance. Change it to 22 MΩ.
Lifting a leg is good to check ones balance preferably the "Crane" method. It is also good to check components.

[Paul Moir]

OK, we may have the tiger by the tail now.  To validate my check could you please confirm with the Horizontal Selector set to "Line SW" that you measure 1.4-2VAC (meter set to AC volts) on the indicated side of C126?  This is the long capacitor you replaced next to V6, and the side we want to measure is the side near the front panel.
If we get that, it looks like something around V6 is bad.  Since the horizontal position control seems to work fine, and everything after V6 is affected by that control, all that is probably OK.
I'm glad to hear your visit to the beach was good.  Ours are still cold and miserable, but they might warm up by the end of July!

[Rickenbackerman]

Paul, I get 1.22VAC at that location with the horizontal selector set to "line SW".

[Paul Moir]

OK, looks like we're making progress then.  I get 1.44VAC here so close enough; something downstream is amiss.

Could you please check the two points A & B on volts AC, with the same setup as before but with the horizontal gain set about halfway.  I get 1.2V at point A and half that at point B.  They're both on the pot so pretty easy to get to from there if it's lying on its side.  That will confirm the V6A amplifier is working.

[Rickenbackerman]

Paul, while you were typing that I was testing every resistor associated with V6 and V7 - everything looks good.

I lifted a leg of C124 and tested it with my DVM as Quarlo suggested - even with the meter set to 2000Meg, the cap charges up then the resistance goes infinite.  So that's not the problem.

To clarify an earlier measurement - R142 - measures 33Meg, but with the leads on my DVM connected directly on the 2000Meg setting I read 9Meg...  so really R142 is about 24Meg.  I really need a new meter (and I've been through a few over the years!).

TEST 2:
Point A - 0.012VAC
Point B - 0.012VAC

It looks like we're on to something.  To check my meter I redid the first test you suggested and now I see about 1.8VAC vs 1.2VAC.  Not sure why it's moving around.  I've looked over every solder joint on this thing at least a dozen times and I don't see anything so I'm thinking I may have connected something incorrectly...

[Rickenbackerman]

Closeup of V6 socket and parts...

[Paul Moir]

Your recapping is a lot neater than mine.  I've got a two 22uF Nichicon radials in parallel there   I also have a very, very fine crack on a trace on V7 which is giving me an intermittent horizontal. 
I double checked those voltages with a 'scope.  There is no DC there and it's a normal sine wave, so if you're reading point A correctly, there is a problem with that amplifier.
Regarding the original voltage; it might be affected by the "Phase" control.  Mine is stuck and I've been trying to free it up.  But if you're seeing anything like 1V at that point you should have a nice wide horizontal trace.  So don't worry too much about that exact voltage.

[Rickenbackerman]

Ha!  (on the neat recapping - I try)

If you carefully scrape the busted trace with the point of an X-acto knife to scuff it up, lay a hunk of small solid core across the gap and solder it on that's the best way I've found to fix a busted trace.

Bedtime here.  Agreed, something is up with V6A.  Tomorrow I'll reflow all joints associated with it and see if that gets me anywhere.  The tube tests fine on my BK747B.

[Paul Moir]

Same here.

And you can play swaptronics with V5 if you want because it's not doing anything with the Horizontal Selector in "Line SW'.

I'll fix that trace just as soon as I remember to bring my soldering iron home.  I have a rather nasty Radio Shack firestick here but I would rather not use it!