Minitor III/IV frequency drifting

[IRS_BDN_MB]

I have repaired many Minitor III & IV's but in recent months I've been getting a reoccurring fault. It only happens on low split VHF pagers. The low split are marked 'B' on the receiver and logic boards. The problem is that the frequency drifts a lot. I’ve seen them drift as much as a few MHz off the programmed frequency. I’ve tried reflowing the entire RF board with no luck. The weird thing is it doesn’t happen to the high split VHF pagers which are marked 'C'. I have tons of spare 'C' RF boards but they are not compatible with the low split 'B' pagers. Its hard to troubleshot any electronics when the schematic is not available.

Is there anyone who has found the cause of this problem?

Any help would be greatly appreciated!

Andy

[Lake Effect]

When you reflowed things, did you remove the square (1/2 inch) shield? I have had many of these not lock on frequency due to the IC under there. Usually it is one leg loose. The end leg nearest the round timer crystal is the usual suspect.

L.E.

[IRS_BDN_MB]

No I did not go to the trouble of reflowing under the shields before now! I just pulled the shield off, reflowed that IC and sure enough it is dead on frequency now.

Thank you for the info!!!

Andy

[Lake Effect]

You're welcom. Glad I could help.

L.E.

[pigpen484]

i have a min iv vhf high band doing this same thing does any one have a pic of what needs resolder or a little more info on it thanks

[aaknitt]

Thanks for the tip Lake Effect! I just did this on a pager that was drifting, and so far it's rock solid again. I've posted pictures of doing the fix here:

http://radioetcetera.googlepages.com/minitoriiifix

Andy

[Lake Effect]

Thanks for the pictures, aaknitt. I didn't have the ability to post them for the previous question so I'm glad you did it. I have fixed many drifting problems on these pagers and so far no repeats.

L.E.

[rileym]

I am experiencing a different one...

I have re-soldered the IC under the square heat sink as suggested, no luck. Also tried completely swapping the RF board for a spare, still no luck. I noticed one of the connectors (the one towards the top) than connects the RF board to the controller seems to sway to the side a bit. Could it be a bad connection there?

The pager does not receive anything on the programmed channel even with open squelch, which does play back snow.
Any ideas?

Thanks,

Matt