My 186 W's dial was stuck, so I took it apart to clean it. Upon reassembly, I noticed that I had the little block of contacts in the wrong place. At this moment, the phone could not dial the numbers 2,5,8, and 0. Everything else worked fine. This contact block is shown in picture A
Now, upon fixing the contact arrangement,referencing from another 186, nothing seems to work. Upon pressing a button, there is a little pop and a lessening of volume on the line. No audible tone can be heard. Upon removing the contact block completely, nothing is heard when pressing a button.
I'm not a GTE/Automatic Electric guy, but all mechanical DTMF dials, regardless of manufacturer, operated on the same general concept. Your 2,5,8,0 issue was the result of one of the sets of contacts around the outer perimeter of the dial that corresponds with the pressing of one of these digits. Each digit operates two sets of contacts to create dual tones (DTMF). One set of vertical and one set of horizontal contacts are closed to blend two tones together. Sounds as if your faulty contacts are located at the top or bottom edge of the dial pad.
As for the second part: On the back of the dial (picture A), one set of normally-open contacts 'turns on' the dial, as in these contacts close whenever any button is pressed to power the oscillators. That set of contacts is either not closing, or your suspected transistor leg is the culprit.
The click/mute of audio when a button is pressed is proper operation. This is an intentional muting circuit to prevent loud tones from being returned to the receiver. This is the result of another set of contacts (also in picture A) that places a resistor across the receiver unit in the handset. This set of contacts is going to be adjacent to the ones on the back of the dial as the one mentioned above. They may be N/O or N/C depending upon the circuit design. The tones are very loud when generated by the dial, so they have to be muted to prevent discomfort when holding the handset to the ear. From what you've said, those contacts seem to be working properly.
You sound like you're on the right track otherwise.
