How buried are those caps? Even though it was working great, I sold my old Tek for fear the caps would go bad. Those things were really buried. It would have been very difficult to replace.

I'm not sure what you mean by buried? It looks like the power supply board can come out with just a few screws and unhooking a few connectors. So if I can get the board out, it shouldn't be too tough to access (at least the PS caps). I foresee it being difficult to get them out but I have a desoldering pump and a decent iron so I'm hoping it won't be too tough. Guaranteed to take a while though.

If anybody knows of good tips for replacing caps I'm all ears for sure.

 

Most manufacturers of that era provided GREAT documentation about their products. It's just a matter of finding it, if the stuff you have isn't correct.

This shouldn't be too hard for you, I'd think. They were MADE to be taken apart and worked on. Might take some planning on how to gain access, but you're likely to succeed, I think.

No tips - just get in, heat connection, rock them, get them out without ruining the board (probably fine, they were BUILT back then!)...clean the holes and replace the cap. Be sure not to cross any values, ha ha! I find this operation to be pretty manual rather than 'fine', if that makes sense. Just respect that PCB and the parts on it that are nearby! )

 

I'm not sure what you mean by buried? It looks like the power supply board can come out with just a few screws and unhooking a few connectors. So if I can get the board out, it shouldn't be too tough to access (at least the PS caps). I foresee it being difficult to get them out but I have a desoldering pump and a decent iron so I'm hoping it won't be too tough. Guaranteed to take a while though.

If anybody knows of good tips for replacing caps I'm all ears for sure.

I mean mine were buried inside the scope. I would have to dissemble half the scope just to get to them.

I'm glad for you that it looks easy yo disassemble.

I would remove the supply and take a number of pics. Create a new thread with the pics asking how to proceed. Stick to the subject of just removing the caps. A new thread might get attention of others not following this thread. You want to be real careful removing those caps if in is a multi layer board. Get the best advice possible before proceeding. Not that Mike did not give good adice , you just might want to get more input.

Good Luck!

 

Clip the dead ends of the cap leads off as short as you can get them. Less length to wiggle them out of the solder holes. Sometimes it works to cut the body of the cap into little pieces and remove one wire at a time, but that is a last ditch, desperate thing to do.

 

The best input of ALL would be the service manual, which will provide step-by-step instructions for taking out the board in question.

When I picked up my scope, I got very lucky the guy on Ebay sent them along!! I had to dig in and find/replace ONE blown diode that was killing a channel. Without the procedures lined out in the manual, I'd probably have done something very wrong and broken something.

Spinnaker is totally right - if you can locate a 'guide' online specific to your scope, I think you'll have a MUCH easier time of it. Doing the caps themselves is probably going to be easy. Disass'y, reass'y without damaging something...now, THAT could be a very delicate and intimidating thing for anyone!

Did you try to find the model on Youtube? There's more on there than many ppl know about...you might get lucky, get to watch someone take on apart!

 

I know when I work old stuff sometimes its hard to.get the solder to reflow ..What I suggest is to scrub the board with a brass wire brush and achola....

 

hard to.get the solder to reflow .. scrub the board with a brass wire brush and achola....

Misspelling? Did you mean a choka chola?

 

That looks an easy one to fix. All the caps look low voltage to me.

I would replace all the electros in the second photo, that are to the right of those two black heatsinks. If you can, get 105'C rated electros.

You also need to clean the corrosion. It will probably be causing leakage and could even be the cause of your ripple. Try a toothbrush and some metho or isopropyl alcohol. Keep brushing and rinsing until it has all washed away from the PCB, don't just brush once and smear it around.

The good news is that the PSU is a big old simple linear supply that is very easy to access the parts and easy to check and diagnose.

 

Could be PSU noise. Often you need to replace a few caps on old scopes to get them working tip-top.

A bouncy squarewave as described could easily be superimposed with mains hum due to flaky ground return/shielding.

If it was still present with nothing connected to the input, it would make setting the astig pretty difficult.

 

A bouncy squarewave as described could easily be superimposed with mains hum due to flaky ground return/shielding.

If it was still present with nothing connected to the input, it would make setting the astig pretty difficult.

Not sure how to check for that particular issue... but suppose after I get these caps replaced i'll look to that next if the issue remains.

I've removed all the caps from the PS board. It went very easily actually. I have attached a few pics. Note the second pic with the close up on the largest capacitors... quite a bit of corrosion. I will get some 90% or higher isopropyl and get that cleaned up, along with the rest of the board. I did notice that one of the caps (C304) has three leads. Would it be okay to replace this with a normal 2 lead cap of identical voltage and capacitance? I am ordering 105C capable caps as suggested by a previous poster.

Finally, I've attached a third picture of the other board (sweep circuit maybe?). This board doesn't look as bad, perhaps didn't get the spill/contamination that seems to have hit the PS board primarily. Would anybody recommend pulling those caps as well? My plan is to recap the power supply board and see if that fixes the problem.... then perhaps look the shielding and this second board.

All and all the work has been easy and very educational. Looking forward to getting the new caps in and putting them in. Thanks again for all the help guys.

 

I also contacted B&K and they quickly sent me a parts list and a schematic. Unfortunately the quality is pretty bad and it is tough to make much of it. I contacted them again to see if a service manual was in print at any point. I think I will need one to calibrate this thing. Anyhow, I'm attaching the PDF in case anybody else who finds this thread through similar issues can make use of it.

 

Just fwiw... if you have a local HVAC shop, they might have a product called * Fantastic Foam "

It is quite similar to the * Scrubbing Bubbles * bathroom cleaner, and a newer non-chlorinated version of a former product.

a generous coating, let the foam about half dissipate, then go after the corrosion with a toothbrush. rinse with distilled water, and bake in a 150°F oven for a couple hours... then give a good going over w/ dry compressed air.

I know this sounds screwey, but it WORKS !!!

 

Owner's manual: http://radiorestorer.com/bkt1466scope.PDF
You can ORDER rolleyes a service manual here: http://www.bkmanuals.com/1401-1500.htm

I can't see where the 'mystery cap' is on the schema...I'm going to assume it's not a 'cap can', the parts list says it's a normal 200V cap, so there should be one "non functional hole" in the PCB. That may have been to keep it from vibrating (?) Anyway, if it was me, and there wasn't a trace going somewhere, I'd put a normal cap in and maybe hot glue it down after. Check for polarization...
http://www.bkmanuals.com/1401-1500.htm

 

Not sure how to check for that particular issue... but suppose after I get these caps replaced i'll look to that next if the issue remains.

.

Most scopes have a switch on each Y input for AC or DC coupling - some have a shorting position that isolates the input connector and shorts the input circuit.

If it doesn't, a spare connector with a shorting link soldered directly to it would accomplish the same effect.

Then any remaining vertical deflection would be due to some fault in the scope.

 

Update on this. I replaced all the caps on the power supply & vertical amplifier board (they are all on the same PCB). I got everything back together and the signal does look cleaner but i am still getting a bounce/ripple. Here is a picture of channel 1 set to ground with nothing connected and 1ms sweep. I have it on frame to hold the ripple I am seeing there but this can be seen in both channels. At higher levels (10ms) sweep, it just starts to look like a blurry line where the ripples start to run together. It is best observed in the 2-1 ms range.

My next thoughts were to go ahead and replace the caps on the horizontal amplifier since they look pretty rough too but i have doubts this will solve the problem. I have noticed that many of the leads on the transistors on the vertical amp/PS board are somewhat rusty/worn. Could a faulty transistor cause this? Could i use a multimeter to verify the transistors are working? Other thoughts on what to check?

Thanks for the continued help guys.

 

I am also aware that the signal is a bit slanted. That is from me messing with the trace rotation. Didn't notice I didn't put it back till looking at the picture.

 

What seems strange is the frequency of the strange ripple. It looks to be about 300Hz. Have you compared that to a 60Hz signal to see if it an even multiple?

 

Update on this. I replaced all the caps on the power supply & vertical amplifier board (they are all on the same PCB). I got everything back together and the signal does look cleaner but i am still getting a bounce/ripple. Here is a picture of channel 1 set to ground with nothing connected and 1ms sweep. I have it on frame to hold the ripple I am seeing there but this can be seen in both channels. At higher levels (10ms) sweep, it just starts to look like a blurry line where the ripples start to run together. It is best observed in the 2-1 ms range.

.

On a Kenwood/Trio scope I worked on a while back, there were some anomalies on the trace once I'd got it going - turns out I'd forgotten to refit a couple of screening covers, the sensitive circuits were picking up radiated emissions from the SMPSU.

 

What seems strange is the frequency of the strange ripple. It looks to be about 300Hz. Have you compared that to a 60Hz signal to see if it an even multiple?

Unfortunately Bill this is my first Oscilloscope and I have spent all my time trying to get it working. I therefore have no working knowledge of how to use one . I am doing some reading the basics of scope operation but I don't yet know how to read the frequency or create a 60hz signal for that matter.

I have ordered probes and plan to do some basic scope tutorials but I feel like I might be at a slight advantage since I've got this noise going on. Hopefully i can resolve it before the probes get here.

 

On a Kenwood/Trio scope I worked on a while back, there were some anomalies on the trace once I'd got it going - turns out I'd forgotten to refit a couple of screening covers, the sensitive circuits were picking up radiated emissions from the SMPSU.

Hmmm... well I haven't touched any covers other than the main metal cover which I removed to pull out the PCB board. I wonder if it could be some kind of shielding issue though. Perhaps the transformer acting on the signal?

Any thoughts on whether a bad transistor could cause this? There are a ton of them and I'd hate to replace them all (although they are in rough shape) if I didn't need to. Although the caps came out and went in without any trouble at all which is reassuring.