Re: 545 HV won't oscillate 100% of the time.


Don Black <donald_black@...>
 

Does anyone know if the leaking oil is PCB?

Don Black.

On 09-Dec-13 9:48 AM, Daniel Koller wrote:
 

Yup - I agree!  I Ended up replacing C800, C803, C805 and C806 - basically all the remaining bumblebees in the primary circuit of my HV power supply.  The two 0.001 uF caps were clearly leaking oil on the photo I posted earlier.  What was less evident, and I didn't notice until I got some better lighting, was the crack lengthwise across the 0.01uF cap, second from the top in: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781

...and the 0.047 uF cap was similarly cracked on the bottom.  Yet ALL tested just fine at low voltage on my new Chinese tester.  But apply any voltage to them whatsoever (~>10V) and they all leaked to different degrees.  They all had effective resistances of ~~10's of Megohms, so at 100V, ~~10  micro amps leakage.  I'm glad I did not get rid of my old Eico 950 tester!

  So, now my HV works, but with a catch.  It turns on by itself about 1 minute after the tubes turn on.  That's about 1 minute after the B+ relay clicks on.  I can occasionally accelerate the turn-on by jostling the intensity knob.  So, it's not 100% fixed, but I am fine with this.  I don't have the patience to troubleshoot further since it is working well when warmed up.  I'm thinking a weak 6AU5 is the culprit here, no?

  In addition I replaced the vertical output capacitor because I measured ~20V DC at the vertical signal out terminal with no vertical deflection on the screen - leakage.  There are a couple oil filled caps left in the power supply that don't appear to be cracked or leaking, and I am just going to have to leave them there for now.   I'll stock up on replacement parts in the meantime.    All voltages are dead on - I'm not touching the power supply.

  Finally, I now understand those extra components in my photo.  The 33K (not 2.2K - it's hard to tell the orange from the red) and the 470 pF cap seem to have been added in some sort of factory refurb.  These are present in the 545A schematic, so it seems my 545 was partly upgraded to a 545A.  That probably also explains the Silicon diodes on that board in the power supply.

  Dan

On Sunday, December 8, 2013 9:35 AM, "bonddaleena@..." wrote:

>I have replaced literally BUCKETS full of BBOD, Bumblebees, wax caps, etc. I have NEVER seen a single one that would pass a leakage test at rated voltage.
>They might 'test' fine for VALUE on my NIST traceable bridge, but they all leak at HV.
>
>As the Prez would say:
>
>"PERIOD!"
>
>ha ha
>
>ron
>N4UE
>
>
>
>
>
>
>
>-----Original Message-----
>From: Don Black
>To: TekScopes
>Sent: Sun, Dec 8, 2013 4:17 am
>Subject: Re: [TekScopes] 545 HV won't oscillate 100% of the time.
>
>

>Oops. I meant eBay bumblebee and black beauty caps, not tubes. Freudian slip??
>
>Don Black.
>
>On 08-Dec-13 8:09 PM, Don Black wrote:
>

>>I hope you get it sorted out Dan but I was being facetious about the eBay tubes advertised as tested good. I wonder what tests were done? I noticed another ad for similar caps saying they were tested OK on a bridge. No mention of leakage or if the bridge had to be adjusted for losses. Maybe I'm just getting cynical in my old age.
>>
>>Don Black,
>>
>>On 08-Dec-13 10:33 AM, Daniel Koller wrote:
>>
>> 
>>>Hi all,
>>>  My caps probably are bad.  When I first got the
                  scope around 1980, I learned about "black beauties"
                  and had to replace them in the power supply, but I
                  think I recall being told that the bumble-bee types
                  were fine, so those stayed in.  Now it looks like I
                  have leakage from them in the HV power supply.  See
                  the attached photo
                  here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
>>>The two shiny black 0.001 uF caps stand out because
                  they are coated in oil.  You can't see it on the
                  photo, but there is a film of liquid oil between the
                  middle cap and the 56K resistor below it.  Those two
                  are coming out but being a big fan of "don't mess with
                  it if it ain't broke" I might leave the other caps in
                  unless there is an obvious failure. Mind you, my scope
                  works well when it does turn on.
>>>
>>>But I've had some other modifications it seems.
                   What's that square cap on the left and the 2.2K
                  resistor doing there?  I'll have to trace the circuit
                  to see where they were put in and why.  Maybe that was
                  a long ago patch for the oscillator failure?  Or the
                  cause of it now?
>>>
>>>I see now why I had originally thought my scope was
                  much younger than it is - before I learned from the
                  group here that the "brown" Teks were pre-1954.  There
                  is this circuit board in my scope:
>>>http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052
>>>Someone seems to have made factory improvements circa
                  1967.   What was in its place before this?  Is it
                  possible my additional HV circuit components were
                  placed in the same upgrades/refurbishment?
>>>
>>>Back to the shop.  I've got an hour before guests
                  arrive!
>>>
>>>Dan
>>>
>>>On Saturday, December 7, 2013 10:58 AM, Don Black wrote:
>>>
>>>>I'm not so sure. Yours may be faulty, these are
                  tested good so they must be a rare animal.
>>>>
>>>>Don Black.
>>>>
>>>>On 08-Dec-13 2:31 AM, Daniel Koller wrote:
>>>>
>>>> 
>>>>>I'll check and see what's in there.   And when
                  I take them out, I'll sell them on e-bay to an
                  audiophool!!
>>>>>http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26
>>>>>
>>>>>(No affiliation with the seller!)
>>>>>
>>>>>Dan
>>>>>
>>>>>On Friday, December 6, 2013 11:27 PM, Chuck
                  Harris wrote:
>>>>>
>>>>>>Most of the time with the 545, the problem
                  is the
>>>              black beauty oil/paper
>>>>>>tubular capacitors used for the HV
                  filters.  They
>>>              always go bad, and if
>>>>>>they haven't been replaced, you must
                  replace
>>>              them.  Ceramic is fine.
>>>>>>
>>>>>>There is also a BB cap that is in series
                  with the grid
>>>              feedback winding,
>>>>>>and another in parallel with the plate
                  winding.  Both
>>>              must go.
>>>>>>
>>>>>>-Chuck Harris
>>>>>>
>>>>>>Daniel Koller wrote:
>>>>>>> Howdy,
>>>>>>>
>>>>>>> The recent discussions on HV repairs
                  has me
>>>              thinking I should look into the issues
>>>>>>> in my 545 (not A or B, old style
                  square case).  
>>>              It works very very well, but
>>>>>>> about half of the time, increasingly
                  more, the HV
>>>              circuit will not oscillate.  If
>>>>>>> I pull the plug-in out and drop it
                  back in, it
>>>              will work.  I know this is not a
>>>>>>> recommended option!  Alternatively,
                  if I shut it
>>>              off and wait for it to cool, it
>>>>>>> will work when I turn it on with
                  about the same
>>>              probability, or a little less.
>>>>>>> Once the scope is on it's up to spec.
>>>>>>>
>>>>>>> The 6AU5 is not brand new, but is
                  good.  It was
>>>              replaced recently with no
>>>>>>> improvement.
>>>>>>>
>>>>>>> So, suggestions as to where to start
                  on this
>>>              intermittant problem are welcome.  Is
>>>>>>> there anything I should look for or
                  measure that
>>>              might indicate what is getting
>>>>>>> tired?
>>>>>>>
>>>>>>> Dan
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
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