No trace on Tektronix 465 scope

[enochsmoken]

I bought a used Tektronix 465 It will power up but I get now trace. Pulled cover off and found a blown fuse F1419 on the 15V unregulated line. I bought the service manual but I’m having trouble tracing this down.
Thanks,
Brad

[Edd]

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Sir Brad . . . .(ley?)

Do not go to jail . . . do not collect 200 dollars . . . instead go directly . . . . to 'ole ala BAMA mirror site and get the WHOLE 465 manuals FULL package as:

http://bama.edebris.com/manuals/tek/465(2)/

Then flip thru 'til reaching Adobe page 228 and just to the right below and off center of that page excerpt, you will find ye referenced fuse in the unreg 15V supply line .
It is feeding power to the switching power supply below.
First suspect would be the power switching transistor Q418 at the very bottom, should it be shorted or leaky.
Now a potential CAUSE of its failure could be the Q1419 electrolytic filter in that supply line deeee-veloping high ESR and corrupring the purity of that feed in 15 v supply, and the Q1419 being the end receptor of that trash, and failure of the unit.
Next consideration would be the secondary load lines thru diodes CR1421 and CR1427 on the right side of that T1420 transformer (shudder-shudder . .if ITS bad ), however these are quite high Z supply sources and derivatives of the -150V and the -2.45KV CRT ultor voltages . . . and with even the little CRT filament chiming in . . . me too . . .ME TOO !.
Otherwise, the balance left is the drive circuitry for the base of the Q418 , in the form of the Q1404--8--13--14--16 cluster.
Thats it for info on this trip . . . . . What say ye ?



73's de Edd
[email protected] . . . . . . . . (Interstellar~~~~~Warp~~~~Speed)
[email protected]. . . . . . . . (Firewalled*Spam*Cookies*Crumbs)



One time I went to a drive-in in a taxi cab. Seeing that movie cost me $95 ! ! ! .



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[enochsmoken]

Edd, Que pasa amigo. Q1419 checks out ok. The capacitor C1419 is actually two 24µf Tantalum Capacitors in parallel. I found one of these to be shorted. What is a good replacement cap for these? Does it need to be the same? The two 24µf Tantalum Capacitors in parallel? The parts list calls for one 47 µf.
Thanks,
Brad

[Janitor Tzap]

Edd, Que pasa amigo. Q1419 checks out ok. The capacitor C1419 is actually two 24µf Tantalum Capacitors in parallel. I found one of these to be shorted. What is a good replacement cap for these? Does it need to be the same? The two 24µf Tantalum Capacitors in parallel? The parts list calls for one 47 µf.
Thanks,
Brad

Hey there Brad,

Hmm.....
Has this Scope been repaired before?

If the schematic calls for a 47uf capacitor.
Then using just the one capacitor should be fine.
It's possible that the two 24uF's was done as a quick fix.
{Being that Tantalum's are rather costly.}
Or are there spots on the PCB for mounting them?
{Sometimes on early, or later runs of the PCB.
they will make changes, to cut costs.}
In any case those Tantalum's don't go bad very often.
So, start checking the rest of the drive circuitry and such for more possible damage as Edd has indicated.

Good Luck with it!


Signed: Janitor Tzap

[enochsmoken]

Janitor Tzap I don't think this has been messed with. After some research I found that, after a certain serial number Tek replaced the 47µf cap with two 24’s. I would like to know if there is a replacement for the two Tantalum Capacitors.
Brad

[Janitor Tzap]

Janitor Tzap I don't think this has been messed with. After some research I found that, after a certain serial number Tek replaced the 47µf cap with two 24’s. I would like to know if there is a replacement for the two Tantalum Capacitors.
Brad

I looked at DigiKey and found 47µf Tantalum Capacitors.
Here's they're Capacitor look up chart.
http://search.digikey.com/us/en/cat/cap ... lum/131082

The 47uF Tantalum will work for a replacement.
BUT....
You need one that will match the Voltage and ESR rating of the current 2 24uF Tantalum Capacitors.

Thus...
A 47uF Tantalum, 20Volt, +/-5%Tolerance, 125c Temp, Through Hole Radial or Axial lead.
Should work as a replacement for the two 24uF Tantalum Capacitors.



Signed: Janitor Tzap

[haklesup]

The part substitution was probably a supply issue. They probably got tired of fixing failed electrolytics that they went to the tantalum. Hypothetically two tantalums could give you lower ESR than a single electrolytic but I have no idea if thats what they were going for. They also tend to be more stable WRT theur value but are usually more expensive (but not always depending on supply situations and bulk buys)

I'm suprised that shorted tantalum cap did not explode, they usually do. Tantalum caps are pretty reliable until you hit them with a large enough revers bias pulse, then they prime like detonators.

[dacflyer]

i have had a few flame up and go super nova...lol...

[Edd]

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Meeester Brad . . . . .


In ref to your ¿ ¿ ¿ "Que pasa amigo" ? ? ? ?:


Ehhhhhh Gr i i i i i n n n n n - go . . . . . now, with even more PREEE-cise info:



May I now say . . . . . WHASSSSSS UUUUUUUUU U U U U U U P P P P P P P P? (a la TV commercial of the past).



(ROTFLOL . . . .BAGut )



I don't have an opened 465 (of my two owned units plus a 466 storage ) unit for inspection . . . . but " THE ZAPPPPPSTER " was referencing you into a tantulum chip capacitor.

I had a conventional leaded wire cap design in mind . . . . now, which type is your unit using ?

In testing switch mode power supply "ewectwonics " (a la Fudd ster) and using either the pinkie touch test to the case of an electrolytic . . . .or an IR thermometer, if I am finding a unit running quite warm, I have always been able to make it absolute "cool city" by the placement of two paralleled units for that single unit. It knocks down ESR akin to the " Law of Inverse Squares".

I too was surprised when you mentioned a failed tantalum unit, but then, I mostly use WET tantalum slug units instead of the common tantalum foil units.

I have some (wets) in my extensive parts cache that date back to the 60's but still ESR out as perfect, but most of my stock is in 70-80-90's vintage.

Ohm out the rest of the circuitry on down that 15 unreg supply line that you are working with . . . . but could you be so lucky as to get out with only that cap and a fuse . . .whOOOOOPPEEE !

Thasssitttt . . . . .

73's de Edd
[email protected] . . . . . . . . (Interstellar~~~~~Warp~~~~Speed)
[email protected]. . . . . . . . (Firewalled*Spam*Cookies*Crumbs)



Efficiency is a finely tuned and highly developed form of laziness.


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[Dean Huster]

The Tek 400-series use no SMT components anywhere. Most likely, Tek figured that they were having failures relating to voltage on the original 47µF part and replaced it with two 24µ caps in parallel with a higher voltage rating. There may have been a size restriction that kept them from upping the voltage rating on the original part and instead used two smaller ones in parallel. You're working on the underside of the chassis where it can be a tight fit against the inside of the case.

In case you haven't figured it out yet, the way to take the case off and put it on is to flip the scope's bail handle so it's over the top of the case, install the front cover and stand the scope on its face to remove the six screws in its backside. Remove the four feet and plastic retaining ring and then slide the cover straight up and off, kieeping the line cord so it wont drag against the cover edges. Putting it on is just the reverse. Make sure it's seated in the front casting grooves ... when it is, the case rear end of the case will be flush with the read edges of the rear panel.

All screws used in the "new" 400-series are Pozidriv. A #2 Phillips will work, but a Pozidriv bit is SOoo-o-o-o much better ... has a much nicer feel.

[enochsmoken]

I replaced the two 47uF Tantalum with one aluminum 47uF 50V and all is well… So far
Brad