cap tester repair

[pete g]

Ok, those readings make a lot more sense.

I would be interested in the resistance of R6, a 1.5MΩ resistor, possibly connected to pin 8 of the 6BN8.

it measures 1.8meg

 

[(*steve*)]

Hmmmm... That's not wildly high, but it may be worth replacing. I doubt that it is causing the current problem, so it's not something I'd do right now (unless you have a replacement 1.5M resistor on hand).

Try the tests that Edd is suggesting. I'll take a deeper look at the schematic. There may be other components that could cause this bias problem.

 

[pete g]

Hmmmm... That's not wildly high, but it may be worth replacing. I doubt that it is causing the current problem, so it's not something I'd do right now (unless you have a replacement 1.5M resistor on hand).

Try the tests that Edd is suggesting. I'll take a deeper look at the schematic. There may be other components that could cause this bias problem.

HI EDD, I just realized what the diagram is. will be using it. thanxs.

 

[pete g]

Sir pete geeeeeeeeee . . . . . .(and Sir Steve as an interested spectator up in the 56th tier of the Peanut Gallery )

I'm going to speed you forward a bit . . .with your having said that the working ? unit has developed this situation with time.

At the top you can see the RED - GREEN - BLUE - PURPLE arrow paths . . .Yellow brick roads . . ..
Lets take the RED arrow one first and see it taking all of the B+ that the 6AX4 can hit it with and travelling down and to the right to the R30 end of a daisy chained series of dropping resistors that end up at an offboard R15 to ground. That gives the #17 rotor connection the capability of picking off some selections from ~3Vdc on upwards of 600 Vdc.
The switch selected voltage then routes down the ORANGE arrow path to the RED designated BRIDGE- DISCHARGE - LEAKAGE switch and its A and B sections.
Now, since we are only concerned with the LEAKAGE aspect, only those switches connections made, are being depicted with the RED-BLACK jumpered connections. On the left A section, we can then see that the ORANGE arrow path then connects into an R40 10k/10W resistor and exits and continues down to the front panels + terminal of the RED 5 way binding post connector.
Sooooooooo . . . now we have the tested capacitor between the two posts and we just now have to see what happens to that left negative lead and how it eventually gets grounded, along with its creating voltage metering.
Now . . . . one additional aspect, is that the same A section switch that we just evaluated . . . additionally . . . connected your - terminal of the BLACK 5 way binding post connector into the PURPLE arrow buss up at # 10 and 11 of the same A switch section.

Now that we see that both sections of the test capacitor are connencted in, lets go up to the top of the page and note that we have the 1st grid of a 6BN8, the plate of a 6BN8, the 1st grid of the triode section of the 6E5 and the cathode of the 6E5 that will be receiving remoted connections via the GREEN - PURPLE and BLUE arrow paths.
Lets start at top left corner at the plate of the 6BN8 where its plate takes the supply voltage from the 220K . . .in that time freame, with it probably being a molded carbon composition resistor.
( The vendor probability factors are . . .Ohmite 28% - Stackpole 18% - IRC 24% - Allen Bradley 29% ).
Check its value to see if it hasn't drifted upwards with time. Then move down the GREEN arrow path to the R7 with its probable .0001 % failure rate
Then follow the GREEN arrow path to the right til the drop down to our now familiar switch, but viewing its B section this time and GREEN arrow goes in #2 and out 4 and back up the path justhaving been taken, but this time it is entering into the 1st grid of the 6E5.
Now . . . . . Ladeeeez and Gentlemen . . . what we do seem to be having here . . . . are being a direct / resistively coupled dual amplier stages.
I ask you . . . .doesn't that high and "odd" level of + DC voltage on the grid of the 6E5 seem more normal / equatable now ?
I say yes . . . but not with that cathode of the 6E5 being directly grounded.
So now we can see that the cathode of the 6E5 is being " remoted " via the BLUE arrow path down to a right angle branch to the left and also straight down to . .guess who switch . . . and in its #12 connection to ground.
BUT that is being ONLY if we were in bridge mode, in our case now, we use that left BLUE arrow branch and transverse to the left and drop down to the YELLOW marked up TYPE (of capacitor) switch with its A and B sections and we make connect into the #1 contact.
Now this TYPE switch pair is being different than our far right B-D-L Switch that were checking out, that just always remained in its switch connections, while testing for LEAKAGE.
In its present situation, it has now received the cathode of the 6E5 and is routing three series resistor sets to ground.
Therewith, you now have a variable cathode resistor cluster serving as your 6E5's cathode resistor.
Now you can see the significance of the order in which you adjusted the R43 - 44 - 45 trim pots and their potential interactions with each other.

Lets watch the switching action related to this TYPE switch section B

Move the switch to ELECTROLTYIC position . . . . .
The downcoming BLUE arrow cathode line flows into switch #1 and out #5 and into R45/39 cathode resistor pair to ground.
( Ignore the 2-5 path . . . . as its now being open circuit in this switch position).

Move the switch to MIN'LYTIC position . . . . .
BLUE arrow cathode line flows into R43/37 cathode resistor pair and out of them into switch #2 and 5 contacts (which will short across the R44/38 cathode resistor pair, (taking them out of circuit) and then lets the BLUE arrow path continue to connect to the bottom
R45/39 cathode resistor pair to ground
( Ignore the #1-5 path . . . . as its now being open circuit in this switch position).

Move the switch to MIN'LYTIC position . . . . .

BLUE arrow cathode line flows into R43/37 cathode resistor pair and out of them into the R44/38 cathode resistor pair and out of them into
the bottom R45/39 cathode resistor pair to ground
( Ignore both the 1-5 path and the 2-5 paths, as they are both now being open circuit in this switch position).

That was the more in depth aspect, totally being ignored in the HEATH manual expanation of operation.
Now the last one involving the voltage measurement.

You remember . . . . . that we left you with a test cap connected to B+ and the - lead floating and needing a way home to ground, while also being measured with the eye tube.
Go back to the TYPE switch section A and we see that the test capacitors - lead comes in via the PURPLE arrow path and into TYPE switch section A.

These are the flow paths on the A section of the TYPE switch

Move theTYPE switch to the ELECTROLTYIC position . . .

The PURPLE arrow ground path comes across to the left and goes up into #9 and exits 6 and connects into a voltage divider branch of R36 to ground or goes the upper path of R35 which then passes on up to R6 which passes up to the 1st grid of the 6BN8 triode.
( Ignore the # 7-9 path . . . . as its now being open circuit in this switch position).

Move the TYPE switch to the MIN"LYTIC position . . .

The PURPLE arrow ground path goes up into #9 and exits 7 and connects into the R35/R6 voltage divider branch, of which, R6 goes up to the 1st grid of the 6BN8..
( Ignore the #6-9 path . . . . as its now being open circuit in this switch position).

Move the TYPE switch to the PAPER, MICA position . . .

Don't look at the A switch section contacts, cause there is nuttin' happ'nin with them any mo . . . . . instead back track the PURPLE arrow, wannabe "ground" at the bottom.
It will go up into the B-D-L switch B section to #10 and loop thru to #6 and pass up the right extreme side and upwards until it shifts left at the top and it then ties into the 6BN8 1st grid
( I shudda' put a PURPLE arrow up that path) then the arrow path moves to the left to the top of our old friend . . . R6 . . . the top unit of that voltage divider trio.

Subjectively . . . .the top of R6 is your voltage read off point for measuring PAPER MICA CAPS while the lower R6-R35 junction povides the MIN'LYTIC voltage read off and finally the lowest R35 - 36 junction provides the standard ELECTROLYTIC voltage read off.
The selected sample voltages are being fed into that initially mantioned 6BN8 + 6E5 DC coupled gain block to activate the eye tube.

FIO . . . . my designated RED-WHITE-BLUE circles designate a non consequential flow path ending, as they are grounding the cathode of the 6E5 in accordance to two different switched positions functions (in BRIDGE testing)..

Your related " homework " / lab assignment . . . .
Confim R8 220 K as being . . . O.K.
Lift the ground leads of C11 and C4 and re ground with clip leads or temporary use tack soldered soldered jumper wires.
( "soldered soldered " . . . . . I plead fractional / marginal dementia onset ! )
Power up and take the R12./ C11 junctions DC voltage . . . steady? . . . if so . . .then lift C11 ground to see if voltage increases, if so expect C11 to be leaky.
Same procedure on C4 and the monitoring of pin 2 of the 6E5..
That would be the last of the 6E5 readings . . . and by the way . . . .

MY TIMELY TECHNICAL TIP . . .
A "bad " 6E5 may actually be due to a skyrocketing increase of the resistance of the R12 1 meg resistor.
Now . . . .
C3 seems to be just fine, as per your supplied voltage readings.
Check your 680 ohm R36 . . . . .47K R36 and 1.5 Meg R6 resistances.
If 1.5 meg R6 is higher in value, it will shift the eye tubes sensitivity up and make eye opening even harder to accomplish, if even being possible at all.

Now the last parts would relate to a "mis-adjustment"
on the YELLOW TYPE switch, section B there are 3 fixed 47K resistors that have 100k pots shunting acroos each of them. The idea being for the trim pots to end up being just enough lower in resistance to bring the companion fixed resistor into spec.
Hypothetically saying . . . . that the 100K is trimmed in so as to bring the paralleled pair down to 33K.
Now if you check R37 - 38-- or 39 and find a reading of 33k and 5K and 500 ohms, two of those 100K's are grossly misadjusted . . .to too low of values .

Excluding chemically cleaning controls innards . . . . That's about all I am seeing initially.


73's de Edd . . . . .
. . . . . . . . . . .

Dear Abby:
What can I do about all the sex, nudity, language and violence on my VCR and DVD players ?

​

 

[73's de Edd]

MINOR SCHEMATIC LABELLING ERRATA . . .

WHERE ?
On the large UNITIZED schematics, right center half, on the BRIDGE-DISCHARGE-LEAKAGE SWITCH and its section A on the left.

WHAT ?
The RED inset info of the switches closures in LEAKAGE mode is erroneously showing a #3 to # 5 contact connectivity closure, while one sees that it is actually #4 to # 5.

WHY ?
You tell me . . . . . . senility onset ?


Dear Abby:
My mommy is mean and very short-tempered. I think she is going through her mental
pause.

 

[pete g]

yes, I see it. love your jokes.

 

[pete g]

checking out wiring, per your diagram. making good progress.

 

[pete g]

slight diversion. an iguana has taken up residence in my garage. trying to figure a way to get rid of him. I dont't think I want to touch him. ugh! anyway, hve checked wiring as per edd's excellent diagram. no errors found. one quesrion. with the type switch in mini and the volt sw ser at 25v b-d-l in leakage, if I read between pin 8 6bn8 and pin 7 of type sw should I read the 1.5m (r6)?

 

[pete g]

edd, have checked r8 meas 245k. c4 and c11 checked both for leakage at 100v and value, o.k. r12 checked good, also.

 

[73's de Edd]

Sir Pete g . . . . . ..

if I read between pin 8 6bn8 and pin 7 of type sw should I read the 1.5m (r6)?


The voltage designating aspect of the eye tube is related to the left half of the schematic and the PURPLE mark up portions, with one variance, in the respect of there also being a complete loop around with one of the PURPLE arrow path over to the right side.

There is the series arranged voltage divider trio of the R6 on top which goes down and ties into R35 and then R34 goes on down and grounds.
The resistance reading across R6 can vary in accordance as to how TYPE SWITCH section A is set.

If it is in PAPER MICA TEST the switch should not be closing any connections related to those three resistors.

If you then switch to MIN'LYTIC, look and see if your top lead of R6 (same as #8 of the 6BN8 ) is then going into the PURPLE arrow loop going to the right, then going extreme right and down and into and out of the terminals #6 to #10 of the B-D-L switch.
Then it continues to the left until it goes up and ties into #9 of the TYPE SWITCH Section A which connects to #7 and passes over and right up the PURPLE arrow path to effectively short out R6. ( Confirm this)

If you switch to ELECTROLYTIC expect the 47K resistor being shunted across R6. (Confirm this)

So you would want to test R6's resistance value by being in the PAPER MICA position and you could further double check by switching the B-D-L switch to BRIDGE or DISCHARGE position to switch open that otherwise closed PURPLE loop around.
Or, an utter finality would be floating the top or bottom lead of R5 out of circuit for measuring.

If doing that R6 resistance reading myself . . . to preclude any potential soldering heat shifting of R6's value into a change, I would lift / clip / unsolder either joining " PURPLE " wire, on either of the sides that feeds into R6.
That keeps excess soldering heat far- far away from R6.

73's de Edd . . . . .
. . . . . . . . . . . .

Text message found, left on mobile phone . . .
370HSSV 0773H
? ? ? ? ? ? ? ? ? ?
(HEY . . . .you're looking at it upside down, dummy !)

 

[pete g]

o,k, thank you, edd.

 

[pete g]

checking out wiring, per your diagram. making good progress.

steve, I don't understand what this is? do I need to do something?

 

[(*steve*)]

You replied to yourself.

I originally suggested that you check all the wiring to ensure there wasn't a construction error, however you assured us that it was once working correctly.

 

[pete g]

You replied to yourself.

I originally suggested that you check all the wiring to ensure there wasn't a construction error, however you assured us that it was once working correctly.

well, its been awhile since I messed with this thing. to the best of my recollection it worked o.k. but, you know I started to check the line that feeds the grid of bn8, and noticed a lot of noise with some big spikes. as far as the wiring I checked , and can"t find errors. can the noise on the grid, be the problem? I do have an old sencore sc61 scope that I used to scope that line. I disconnected the lines on pin 6 & 10 on the bdl switch and the noise is still there.

 

[(*steve*)]

I reviewed an article recently that spoke of the experience of those who worked for Heathkit "fixing" problems caused by people's kit construction.

The observation was that, very frequently, problems were resolved simply by fixing poor soldering -- dry joints being a common issue.

Another observation was that almost every kit had at least one wiring error (wrong component, something connected to the wrong point, etc).

If you're seeing noise, I would certainly be checking for poor solder joints. This is especially true if the noise can be affected by mechanical action.

 

[pete g]

well then, i'll resolder all the joints.

 

[pete g]

I resoldered all connections. I hung a 22ufd cap on the line that feeds the bn8 grid. that got rid of the noise and also enabled me to calibrate the min lytic position. the mica,etc. position still is a problem. somrtimes it will calibrate, but then open again? that's it for now.EDD I confirmed both items you suggested. (r6 being shorted,etc.)

 

[(*steve*)]

I wonder what condition the switch contacts are in after so many years?

I don't suppose you have any contact cleaner?

I watched a YouTube video of someone building a Heathkit project. They discovered that quite a bit of work was needed to get some of the switched working. The same issue might also apply to the trimpots.

Does the resistance across the trimpots vary smoothly as you adjust them? Do the switches read read a very low and consistent resistance?

 

[pete g]

yes I used deoxit on the pots followed by a lubricant. I did find a wiring error going to the trimpots, which I corrected. what happens now is in the mini-lytic and mica,etc., the eye closes when I adjust those two pots when calibrating but then start fluttering open and close. what resistance should I read from pin 15 of bdl switch and pin 2 and 5 to ground of the type switch? what confuses me is that with the voltages so far off the problem should be be obvious. switch contacts good.

 

[pete g]

yes I used deoxit on the pots followed by a lubricant. I did find a wiring error going to the trimpots, which I corrected. what happens now is in the mini-lytic and mica,etc., the eye closes when I adjust those two pots when calibrating but then start fluttering open and close. what resistance should I read from pin 15 of bdl switch and pin 2 and 5 to ground of the type switch? what confuses me is that with the voltages so far off the problem should be be obvious. switch contacts good.

hi steve and edd. I just wanted to thank you for all your help. i'am going to shelve this project for now. your help was much appreciated.pg