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Recently my Tek 2236 began giving a "Control Button Error" message, occasionally at first and now more regularly. Exercising the buttons does not seem to clear this. I ran the CTM diagnostic and everything passes except reading the 1X/10X CH1 sense ring, always indicating "P0" even when the ring is grounded (I don't know if it ever did sense correctly, as I generally used non-encoding probes anyway). In the diagnostic, it reliably reads the positions of all other switches, in particular indicating the push button positions solidly, no glitches seen in the 1/0 transitions in the diagnostic display.

Sometimes with no input I get the "OUCH" message on CH1 volts (even with the input set to ground). Otherwise, all of the CRT display functions appear unaffected.

When the CTM is working, everything works in the alphanumeric display, when not, I get the scrolling "Control Button Error" message, nothing works in any button configuration.

Anyone have any thoughts on this?

I have several Tek scopes, analog, full digital, storage (for a 5L4N) and a 4 channel. However the 2236 is my favorite for general bench work. I miss the built-in frequency counter...

Check harmonica connectors from panel to other boards possible to reseat.

Jon

Thanks for the reply...

After having spent some time going through the CPU/CTM schematics I am inclined to agree with you, it's more probably a mechanical connection problem somewhere. The un-read CH1 probe sense ring is easy to check.
The D0-D7 bus lines on the 6802 are MUXed to many places, not only reading the push buttons but also the ROMs running the firmware. Given that, I suspect an active component failure on a data bus line would kill the entire CTM firmware function including the scrolling "Control Button Error" message. Hopefully it's not some small timing problem in one of the multiplexers...

It won't be the first (or probably last) time I will have reseated connections in my older gear. It's the price we pay to keep legacy equipment operating.
I just need to be particularly careful with the CTM/DMM button extension and Time position knob removal (if necessary). Don't want to break any plastic parts...

A tiny update...
The 2236 is successfully apart. I did find the CH1 probe sense problem, apparently TEK forgot to solder the W9100 connection on the A3 board, the wire was in the PC board hole, just unsoldered. Still investigating for other connection problems that might be the cause of the "Control Button Error" message.

As long as I am inside, I am going to replace the "Riga" filter caps, too.

Riga caps replaced. Scope still apart.
The "Control Button Error" seems to be in the interlocked DMM push button assembly, specifically the last section of the "CH1V" switch. Ohmmeter checks show these contacts as unreliable, probably exacerbated by the buttons being read in a "time slot" along with other data on the 6802 data buss. I had a problem with similar switches in a Sencore "Z Meter", flushing with DeoxIT and exercising them solved that, hopefully it will also be the solution here.
HOWEVER, I was also able to secure a "new" Tek switch assembly (640-7434-00), so I would be able to replace the entire switch assembly. The problem would be in desoldering and removing the old one without destroying the board. Anyone have any "words of wisdom"? There are 40 switch pins to desolder.
Lastly, on the ReadOut ring. The scope now reads the ring correctly when grounded but not with a 10X ReadOut probe. From my research, a 10X probe should provide 11K pin-to-ground resistance to indicate 10X attenuation, which this probe does provide. I am assuming the 2236 complied with the "11K" standard, but I can find no verification of this. Anyone have a 2236 to check this?

Well... Not a cleaning problem. Actually a broken actuator inside the "CH1V" switch section, it was the internal actuator position that was unreliable, not intermittent contacts. So, it will be full replacement of the switch assembly. Fortunately I found one and have it coming.
I desoldered and removed the A14 "Hot Signal Switch" circuit board from the top of the switch module. Tedious work but doable with careful heat application and copious use of solder wick. The switch module itself will take more time...
As Roseanne Rosannadanna said, "it's always something..."

ALLRIGHT!!!
DMM selector switch removed successfully, TEK switch module replacement due in this weekend.
Took me about two hours. I thought it would take days. I will post some pix later.
However, the reason for this is a new toy, the Yihua 948 desoldering station. The tool is a gun with a heated tip (temp controlled) with a hole in it. There is a continuous suction pump in the base unit actuated by a trigger. Just put the tip over (and around) the switch pin, rock it around a bit to insure melting and pull the trigger. Does a really nice job.
I needed to desolder 40 pins to remove the switch assembly as a unit. I had to re-work about 6. after that the switch assembly just fell out. Board is very clean, no smutch like with solder wick. MUCH better than a Solder-pullit. I wish I had discovered this years ago. I am really impressed.
I expect the rest of the repair to go smoothly. Still want to resolve the Readout ring not recognizing the 11K pin on the 10X probe though...