I don't know this tuner. The frequency display works? Any audio? Even on AM should be noise at least.
You can add the prefix uPD or uPC to NEC IC's part markings to better search for them.
I would first check the power supply voltages are OK: +5V, -5V, +12V, +26V etc.
I second look at the synthesiser PLL loop, that frequency is reasonable. You command say 88.5MHz but it can't go there. Varactor diodes acting up or the prescaler not working.
Prescaler 6.25MHz *17 = 106.25MHz or *16 is 100.0MHz. What did you dial in? That seems OK, and I would expect audio hiss unless muting is on.
Look for other tuners using the same basic chipset like
Dual CT1450 to get an idea of how it's done.
You can look at uPD1701 datasheets which is same as the uPD1703 but without the clock feature.
Some other IC info I dug out:
Q402 - NEC uPD1703C, Synthesiser and clock
Q401 -
UPB553 Prescaler divide by 16 or 17, but I can't see full p/n
Q103 - NEC uPC1167C2, FM IF amp and demodulator+AFC+AGC. See also
HA11225, Mitsubishi M51173P
Q201 - HITACHI HA1196, FM Stereo demodulator PLL
Q202 - TOSHIBA TC4066BP
Q301 - SANYO LA1240, AM radio IC
Q104 - SANYO LB1426, VU meter driver
Q143 - NEC D4011BC (CD4011B)
Q410 - NEC D4035C (could be CD4035)
I would stay out of the can for now, all that is in there is a RF amp MOSFET and RF oscillator.