7L13 Sweep Board Cam Switch problems


Jordan
 

I'm having trouble with the Freq Span/Div controls making intermittent contact, and in some positions, no contact at all.

I'd like to remove the Sweep board and check the cam switch contacts, but I'm not sure if I can rely on the service manual given that I have the later version of the 7L13 and the manual instructions for removing the F S/Div controls and the parts blow-up for the control assembly is different.

Any tips, hints, info or links would be much appreciated....Thanks for your time, Jordan...


Jean-Paul
 

We ask the serial number of the plug-in

I have the 7L5 and 7L12 but not 13, however the rotary switches are similar, mechanical shaft encoders not cam switches.

the leaf springs go bad and cause the intermittent issue.

Try contact cleaner, but disassemble of front panel is complex and risky.

Fault is inside the knob mechanism

Bon Chance


jon


 

Jordan:
I have a 7L14 but this board and the switches are the same from what I can see. I had the same problem with the "switches" making positive contact after all of these years. My first pass was to spray DexoIT Gold G5 carefully across all of the contacts and then rotating the Freq Span/Div control from end to end a number of times. Some improvement BUT not reliable contact. Then I removed the whole A1000A2 board ( a real pain in the ass ) and removed the Actuator Cam Switch and then CAREFULLY pressed the "switch" section down while "scrubbing" each contact with a #28 ( for stiffness ) strip of printer paper soaked with G5 back and forth to remove whatever was preventing the gold contacts from making good contact. Then I reassembled the whole board assembly and installed it back into the 7L14. This took care of most of the contact problems but not all. So out came the board again but this time I left the cam switch in place and then checked each contact with a "continuity light" and then "adjusted" ( with very fine tipped tweezers ) the spring sightly to get better contact. Not a job for the faint of heart for sure. Once I was sure that every contact was working properly, reinstall the board again. Finely success for the most part. I had to make yet another pass to get things reliable.
I am just not too sure why these style of switches are not reliable as there appears to be good "wiping" action and the design should work for many years. Both sides of the contacts are gold plated. Has the gold plating worn off? Don't know for sure. Of course I have had this same problem with other 7 series plug ins that use this same design, as well as other Tek instruments which use this design including 465/475.
Good luck,
Bill


Jordan
 

Salut Jon....

I can't speak for the 7L5 or L12, but I can see the switches which are pressed by the raised sections of the roller drum in my 7L13...


Jordan
 

Hi Bill...

I'm looking at the cam roller (for lack of a better term) and the switching, and I can see the contact leafs quite clearly...What I also just noticed is that the pins which P-1260 connects to have rather poor and/or bad solder joints at the pads...I noticed that just touching that connector caused intermittents in the display.

I'll have to work on correcting that before I go any further, and I'll be checking the other connector pins too...

I also have a problem with some of the characters displayed which I'll have to deal with later too...!!!


Jordan
 

I made some progress today on the cam switch after spending a few hours cleaning and re-soldering all the pads and components running parallel to the three banks of cam driven contacts.

After some study of the not uncommon poor, intermittent or failing contact problem, I noticed the rear set of cams, which are driven by the Span/Div control, showed some "flex", and the circuit board itself has no mechanical support at all under the board except for a support at each end. I didn't have any issues with the front set of cams, so I concentrated on the rear section for study.

Just to experiment, I cut 2 small square sections from a vinyl drafting eraser just wide enough to provide some pressure on the bottom of the board while not affecting the rotation of the cams. It made the detent action as the cam "rollers" were rotated much more solid, so I plugged the module back in the 7603 and... Voila..! The cam switch problem is no more.

Not to say that that is the only problem however, I still have some issues with some of the text display characters, and the system still unlocks at Spans/Div less than 100khz. I can see the cal signal drift away and across the screen when I go to a 50khz and lower Span/Div setting.

I'm sure I have some tantalums to replace as well, and it appears that someone had already replaced a few of them before I bought the pair...

Again, any hints, tips, advice or even morale support will be greatly appreciated...!!! 73..Jordan VE6ZT


Jordan
 

Ok...I solved the 1st LO being unlocked problem. I had pulled, cleaned and then re-installed all the "harmonica" connectors on the sweep board, and had re-installed P-1240(?) a 2 pin connector offset by one pin...I re-installed it properly and that solved the unlock problem...

Now I'll go look one more time and see if the incorrect display characters might be due to another offset connector... I know it was working fine at one point..!

73..Jordan VE6ZT