• Get involved.
    We want your input!
    Apply for Membership and join the conversations about everything related to broadcasting.

    After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
    If you use a disposable or false email address, your registration will be rejected.

    After your membership is approved, please take a minute to tell us a little bit about yourself.
    https://www.radiodiscussions.com/forums/introduce-yourself.1088/

    Thanks in advance and have fun!
    RadioDiscussions Administrators

MX-15 Intermittent Oscillation

M

maineengineer

The symptom for this vintage Harris MX-15 exciter is the same as for the classic older Optimod, which manifests itself as a varying (not "locked") audible birdie that can be heard only in stereo and disappears in mono (even when recorded in stereo and mixed to mono), but in this case it's the exciter itself rather than the processor. As it's intermittent (natch), it hasn't yet been scoped, but presumably it's an oscillation in the 38 kHz L-R subcarrier region (modulated oscillator, or main power supply, etc). Perhaps someone has run into this enough times before to be able to offer a "classic" diagnosis and cure (similar to the well-known RF module cap replacement for 200 kHz spurs either side of carrier in aging MX-15s). Thinking "caps" on, please (pun is intentional).
 
Assuming you have re-capped the modulated oscillator and AFC module, have you looked at the power supply with a scope?
 
This is a CLASSIC failure mode for this exciter. The MX-15 is an old exciter and likely needs EVERY electrolytic cap replaced!

Just shotgun the whole exciter-you'll be pro-actively fixing future problems before they happen. Ideally, use 105 C rated caps.
And while you're at it, replace the cooling fan and make sure the regulator chip's screws are nice and tight.
 
Status
This thread has been closed due to inactivity. You can create a new thread to discuss this topic.


Back
Top Bottom