SENCORE SC61 Oscilloscope Horizontal Control Cleaning Advice

[Voxman]

Hello Everyone,
Asking for advice from anyone with expertise and experience cleaning a “scratchy” intermittent horizontal control switch. The oscilloscope works very well except for some of the positions on the Horizontal Sweep switch positions. About half of the positions work ok if you jiggle the control knob but some rarely are useable no matter how much I wiggle the control.
Took it apart to spray some cleaner in the switch and was disappointed to find out it’s a very large SEALED assembly (see photos). I can only see one screw that might be removable but in my experience with parts like this, there has to be more than that one bolt.
Does anyone know if this switch assembly can be taken apart and cleaned? I would look for a replacement part but am quite sure this particular part is no longer in this universe. If I found a used one, there’s no guarantee it’ll work better than the one I have now. I suspect this type of switch isn’t meant to be disassembled but I have in the past managed to correct problems in other defective parts not meant to be disassembled...who knows!?
Well thanks and hope to hear back from some of you older gents with experience in these older pieces of test equation.

Stay Healthy EveryOne!

[Smoky]

I have a box full of SC61 parts from when my scope bit the dust last year.

If you look closely at the other side of the switch, you'll see four small metal tabs that are bent over keeping the sandwich of wafers together.

But before you can take the switch apart, I imagine you'll need to remove the board first and then de-solder the switch.

[Smoky]

[Voxman]

SMOKY,
Thanks for the info! I figured it has to come apart since it was put together!!! It’ll be interesting to see if the contacts are worn or just need cleaning. It never had much use and had been sitting idle for over 8 years before I grabbed it to use in my retirement years. Since it’s sealed ( supposedly ), I don’t see it needing cleaning but who knows, right!?!
I just broke down and bought a new SIGLENT SDS 1202X-E scope to help out on my bench. The Sencore takes up so much room but I’m so familiar with it and love the digital readout for voltages and frequency. Plus it can take those high voltages commonly found in the tube amps I fool around in. I know the SIGLENT is 10x the Sencore scope but it’s more scope than I’ll ever need or use. I opted for this SIGLENT for resale value whenever it’s time to close shop. I checked a few test measurements between the two scopes and was very surprised to see the Sencore was working great. Great stuff, just a monster on the bench.

I’ll post results of the Sencore cleaning in a few weeks if I don’t get side-tracked by some other interest.
Thanks again!
Gary

[Smoky]

What the heck, I haven't had any time to do any electronic stuff in three months...







Definitely dirty as you can see from wiping it with alcohol, but, notice the "arc" spot on this side of the wafer:



To make sure everything goes back together correctly, mark a triangle on the case. Also mark the wafer as soon as you expose it to make sure it goes back together on the correct side. Also mark the shaft because it's possible to be inserted two ways 

[Voxman]

Smoky!
WOW! That’s what I call helping out your fellow man! Never expected to see this disassembled!
You are the BEST!
Ok I better tone it down or you’ll get a big head...

Amazing work! Looking over the photos I’m curious as to why there is any kind of arcing going on in this circuitry, especially something that would cause this issue....but then again I’m not a electronic design engineer. So I see there are 2 wafers removed, so that means there are probably contacts on each wafer section of the switch. That’s going to be fun and like you cautioned, the disassembly has to be done methodically and marked so everything goes back together properly.
Do you see any lubricant within these wafers? If it’s sealed (which I’m beginning to think it’s not totally hermetically sealed) then why are they so dirty? Residue? Lubricant gunk?  What  suggest applying other than something like Deoxit D5 before zipping it back together. You think alcohol is best to clean it with? And how long did it take you to get this switch desoldered and removed from chassis?
Again thanks for all your trouble. You’re one in 789,000 and possibly much more😂

Later!
Gary

[Smoky]

It looked as though a build up of dirt along with whatever lubricant that they used just dried/clogged the contact's surface over time.

I think the arm of the contacts may lose tension too, so level the height of all of them before you close up the case.

Cleaning them with alcohol works very well and I would just put a drop of D5 or G5 on the tip of your finger and smear it around the wafer.

This assembly is not air-tight so dirt can get in over time.

Be careful when de-soldering. I noticed some time ago that the traces on Sencore PC boards lift easily.

[klunkerbus]

Thought I'd point out that is a switch built to a drawing prepared by Sencore.  It's not a switch you ever could buy as a catalogue item.  The engineering drawing specified what contacts were to be shorted together at each switch position. 

[Voxman]

Thanks again for the responses I’ve been privileged to receive! Great resource and great bunch of members!

Thanks so much!
Gary