Yamaha T-720 tuner - problems with auto search

[VMat]

Hi,

I've got a "new" Yamaha T-720 tuner. It doesn't look like it was abused, but it was kept in storage for a long time, according to the previous owner (not a surprise).

It had a few problems, I've fixed the obvious ones, but the last one is giving me a hard time (I have fixed a few audio amps, but never a tuner). I wonder if anyone here has some experience fixing these tuners and can give me some clues.

Symptoms:

1. In FM auto search, starting from a frequency above a certain point, pressing the "Down" button, the search stops at that point (if it can't find a strong station before that), although there's no station there. Usually 90.4 or 90.5MHz (I had it go down once to 89.9MHz instead). There is a station at 90.3 though, not very strong, but strong enough to trigger the CSL, and I do hear it if I manually tune to 90.4 or 90.5 (with noise).
2. In FM auto search, starting from a frequency below that same point, pressing the "Down" button, the counter goes up (!), and stops at the same point (again, if it can't find a strong station before that).

Other things that seem to be relevant:

• I can tune to anything from 87.5 to 108.0 in manual mode.
• The "Up" button works as expected in auto search, wherever the starting point is.
• Both "Up" and "Down" buttons work as expected in manual mode.
• Auto search works fine in AM band (510 to 1620kHz, up, down, each button performing as expected).
• Sound-wise, I like what I hear, although I only hooked it up to the secondary system. There's very little noise, even on weak stations.
• PS voltages are a bit on the high side, but within the tolerances.
• Memory works fine. Stereo detection seems to work fine. I can't tell if the "noise filter" function works or not, can't hear any difference (maybe I should try different stations).

In case you're wondering, the problems I did fix were 1) a leaking capacitor in the power supply (removed it, cleaned the board, replaced it with a combination - didn't have the exact value at hand), and 2) unit not holding the memory after a power cycle (replaced the memory capacitor). Nothing that seems to interfere in the auto search.

I don't have the best resources to work on this, but I'd like to give it a try. I have the service manual, a good multimeter, and a cheap 20MHz digital oscilloscope. No RF signal generator. If I can't fix it, the unit is still usable, anyway - just not as fun.

Any suggestions?

Thanks,

VMat