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Dear all,
I am trying to fix a Tek 577 and would like to check the operation of some specific contacts of the Step Offset Ampl cam switch as well as the 177 Vertical Cuurent/Div rotary switch
I can see from the schematics that the contacts in the cam switches are numbered.
Can anyone tell me what is the convention used?
Front to bottom?
For the rotary switches there are numbers and the letters F or R, which I suppose mean front and rear of each wafer that is numbered.
So 1F would mean the contacts on the front of the first wafer.
Again, what is the convention used?
Thanks

Rogerio,

The F and R are front and rear. One is the wafer closest to the shaft behind the metal wafer with the collar for the shaft. Position 1 is usually the fully CCW (anticlockwise) rotation position.

If you find the diodes leaky to the gate(s) of the dual fet, 1N4937 will work. These have very low reverse leakage and are the best ones for the d-c restorer circuits because of the low leakage, low capacitance, very fast trr and have a 600V rating vs. the 200V used in the d-c restorer circuits. Going higher in PIV on a diode is fine and sometimes advised (d-c restorer circuits is one example).

Mark

Hi Mark,
Thank you for your reply.
Is this convention used for the cam switches also?
If affirmative, contact 1 would be the closest to the "front" or shaft .
Regads,
Roger

Rogerio,

Contact 1 should be the same on a cam as a rotary switch. The first contact number should be the closest to the front/shaft. Ryder's manuals showed the 1 parts of the switches with layered wafers as the one closest to the shaft/chassis skirt with position 1 being in the CCW/anticlockwise position. If anyone else knows otherwise, correct me. Typing with 180/120 B/P so forgive any misspelling or confusion.

Mark

I ran into this with at least one 7000-series plugin. If I recall correctly, the switch contacts weren't numbered from front to back, back to front, or any other scheme I could identify. It was a bit frustrating and I didn't understand why they wouldn't have been consecutively numbered but it just didn't see to be the case and I resorted to tracing the traces to determine which switch went where.

180/120??!! I do hope you're getting help with that. Take care, Mark.

Barry - N4BUQ

Barry,

Thanks for correcting me about cam switches. I figured they were from 1 to _ from front to back. That would be the logical thing to do. The cam "numbering" I too can get confused with. Out comes the VTVM to find what contact goes where to trace what is needed. Follow traces and parts also helps.

170-190/110-130 has been common especially since 4.2.22. I know it is high Stage 2 and Hypertensive stages. It was a bit lower for three months prior. For those that want to know more about this, use private contact to keep from veering off topic. I do not want to get the moderators mad at me for being out of line. I respect them and others on this group to do such a thing.

Mark

Thank you all for the replyes.
I will try to follow the traces, although this might prove to be difficult in the577 without taking out the PCB.
Regards,
Roger

Rogerio,

It occurred to me after my post is if you question if a resistor in the string is bad, unsolder one lead of one resistor. This makes the circuit an open circuit to anything on either end. Then you can test each resistor to see if one or more need to be replaced. You may have to put the selector to one end, CW or CCW. I have done this like Barry did to find an open resistor in the time base of a 7B92A. In your case, the condenser charging causing the reading to slowly change as it charges through the resistors will not happen. This test can be done in the high voltage bleeder in the crt circuits to find bad resistors.

See if you have any leakage paths causing the problem. If you have already cleaned the area, you can skip this suggestion/question.

Let us know what you find as the problem. I am curious to know. You will find your problem.

David's reference made me laugh. Thanks for the Sat. morning smile. The reference to high tension would fit me since working at higher voltages, usually three digits, is something I have done for many years. For those that know NTSC, my sync circuit lost sync for a while.

Mark

Thank you for your reply Mark,
I have disassembled the entire 177 and checked all the wafers one by one but could not find anything wrong.
The 177 was not meant to be taken apart for cleaning, I can assure you, but I have managed to do that!!!
I used a fine sandpaper to clean every contact of the rotary switch.
After reassembling the resistance readings were as before, but I was able to perform the calibration according to the 177 manual, but I could do that before, so I think that I may be barking at the wrong tree.
So I decide to leave the 177 as it is for now and focused on the "main problem" again, which is:
What is causing the "dot" move down the screen when I flip the 177 switch to R in step 9c of the Vertical Gain Adjustment (of the 577).
It should move up and I should use its position to adjust the vertical gain pot.

My current concern is Step Generator circuit (fig2).

It can produce current and voltage steps but the voltages around Q330, Q324, U220 etc are way off and do not change as expected when I change from REP to SINGLE.
The transistors tested ok with a "digital transistor tester".
I will probably open another thread once I have studied the problem deeper.
Regards,
Roger