Tektronix 2246 front panel repair

[king129]

hello i just recently bought this Tektronix 2246 oscilloscope and im having some troubles with the circled area in the first picture with the buttons and some lights i'm assuming are LEDs that aren't lighting up. ive tried takeing apart this oscilloscope to find out if i need to replace any components and this is as far as ive gotten (picture 2-3). Before i even attempted to take this apart on my own I went through the service and user manual for the oscilloscope I downloaded online, sadly it did not contain any instructions on how to dismantle this oscilloscope. So I stopped and took to this form before I did anything stupid like trying to force my way in I learned that lesson already[emoji28]. If any one knows how to get to this front panel or what might be wrong with my scope please tell me it will be greatly appreciated.

users manual:
https://www.tek.com/oscilloscope/2246-manual/2246

service manual:
https://www.tek.com/manual/2246-service-manual



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[rf+tech]

Hi king129,

Although this is a singe data-point perspective, I doubt the front panel is the problem. It may actually be the victim of missing signals elsewhere.

I've been down this very path with another 2246 that had battery electrolyte damage – pins eaten away on ICs, resistors and capacitors covered with corrosion. Most importantly were a number of tracks eaten through causing loss of signals.

Before doing anything further, I would highly recommend checking around the two silver oxide batteries, used to store settings and calibration data.

Also, visually check every smt electrolytic capacitor for leakage, then take a soldering iron, heat one pad. If it smells like dirty socks - it's leaking. Replace *all* of them, cleaning the pcb area thoroughly in the process.

The two series-connected silver oxide cells can be replaced with a single CR2032 and holder and a little creativity.

And to address your question about removing the front panel, I seem to recall it presses out from the back side, same as the 2445/2465. A little finger pressure here and there should get it moving.

Do keep in mind that the scope will need a full calibration, if the original cells are flat or removed with the scope turned off.

RF+ Tech

[king129]

Thanks for the advice ill try it out tomorrow. but as for the poping out you mentioned on the front pannel can you tell me how to do that step by step for future reference and for anyone who has tried what you just said and it didn't work so we can help the next guy out.

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[rf+tech]

Removal is as simple as stated, but is not covered in the 2246 manual.

From the TDS640 manual:

Lift the front panel assembly out of the front subpanel until you can reach the interconnect cable connecting it to the processor/display board.

Disconnect that cable at J2 of the processor/display board. Disconnect the flex board connector at P3 of the front panel assembly. (The flex board is part of the display frame assembly.)

Finally, lift the front panel assembly out of the front subpanel to complete the removal.

The only additional point being the panel is a friction fit, surrounded on all edges by finger stock. May require moderate pressure to get it moving. Obviously, jack and plug numbers may differ.

Attached photo should be self–explanatory.

RF+ Tech

[JimG]

my Tek 2245 has screws i can see on the back side of the panel to remove the trim ring before the front panel can be removed.

[king129]

where are the screws at could you please take a picture and share it with us?
i know you said on the trim thing but where on the trim thing
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[JimG]

these 2 screws look like they go into the bezel/trim, they may just be for the CRT.  i tried to pull mine off and the trim is held on by something.  and it looks like the entire face is one piece. this is a new unit to me also, didn't really want to tear into it yet with 2 others in the works now lol

[king129]

Ah those screws did you ever find a way to get out the the screw from the first image the one on the end of the bezel/trim. I couldn't do it with the interchangeable screwdriver I have at home if you could tell me what i can use it would be greatly appreciated.

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[JimG]

1/4' nut driver with a t15 in a bit holder and wobble 6"extension

[king129]

thanks.

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[king129]

rf+tech im about to start takeing unscrewing the boards to check everything you mentioned ill let you know what i find.

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[rf+tech]

Thanks @JimG re the screws. I've sold the 2246 several years ago.

Later Tek scopes have a snap-off bezel



@king129 if it is of help, here's an image from the 2246 of the original mess.



HTH,

RF+ Tech

[king129]

i haven't fully taken out the board ill send you some pictures in a bit of what it looks like though i don't see any sings of corrosion yet

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[king129]

the first 10 are the bottom pbc.

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[king129]

top pbc.


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[rf+tech]

king129,

If the dark discoloration in the attached image appears to be under the solder mask, then there's definitely some electrolyte damage.



RF+ Tech

[king129]

okay im sorry for not  posting anything yesterday something came up. Either way today I figure out a way to get to the front board which contained a screw beneath it as seen in image one that metal sheet had a screw in it below the PVC were trying to get at that scrrew needed to be unscrewed for me to get at the bottom pbc ill explain how that happened in more detail in a hour at most.

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[king129]

Exclue the in an hour part ill probably have to explain it all when i can put everything back together. Though  rf+tech you were right about this one being blown ill have to check all of the other ones if you think i should just replace all of them with ones that matches their specifications i could do that. I did manage to pull out the metallic tube from the intergrated circuit do you have any advice on what i should do next?

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[rf+tech]

Hi king129,

First, my apologies for such a belated reply - a poisonous spider bite required eight days in the hospital and lots of antibiotics.   

That ripped out through-hole plating may lead to a steeper uphill battle, as some inner track(s) are now disconnected.

Before replacing this capacitor, remove all solder mask from every copper track in the affected area. Razor knife, sandpaper, fibreglass bristle brush, whatever it takes. Failure to remove all traces of electrolyte under the solder mask now, will only lead to more open-circuit tracks over time. Once the cleanup is complete, examine all tracks for places where they have been eaten through and repair as necessary. Examine all vias in the affected area, tracks terminating at via edges may actually be disconnected. In this case, remove all solder from the via and add a strand of wire through-hole to the other side.

Once the repairs are complete, apply CircuitWorks CW3300G overcoat, or CW2500 epoxy, to seal all exposed copper. Then try installing a replacement capacitor and see where things are.

If you do not have a proper vacuum desoldering gun, invest in one. 

Do practice on scrap boards, to improve your technique and avoid ripping out vias in the future. 

RF+ Tech

[king129]

i haven't been working on the scope recently. Finals have really been a pain. Thank you for the advice ill try it out soon. Also im glad you got over that spider bite

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