Schematic vs. Reality: Where Are the Resistors on My Sharp Clock Radio? Model FY-70CH

[lti]

I don't know why I didn't see this earlier, but those are printed thick film resistors. The resistor is the black rectangle in between the pads. I wouldn't have expected them to have good enough tolerance back then, but they were used a lot for non-critical stuff.

That's also a 2-layer PCB with plated through-holes, which I didn't think existed in the 1970s.

[petehall347]

there will be other things not there ..

[TinkerTron]

As for the capacitor coupled output, I got it, thanks! So if I connect a speaker, should I expect that DC voltage to disappear? And would measuring across the speaker terminals with the speaker connected give me a better idea of whether there's an actual DC issue?

But also, am I correct in assuming that the only resistors actually needed for this circuit to work are the ones physically present on my board? Even though the schematic shows around 30 more resistors? I may be a newbie, but this seems like a big discrepancy to me (?).

[petehall347]

its just a variation like that board can be used for other models .

[TinkerTron]

here's a picture I took of the actual board. It looks kind of "unpopulated" to me...

[TinkerTron]

Oh, that's excellent info. Thank you very much! I'll test it with a dummy load.

What about my "ghost" resistors? Would you happen to know something about that?

[petehall347]

i cant see the actual boards

[petehall347]

its capacitor coupled output so you will see dc at the speaker connections without a speaker connected

[TinkerTron]

Hey everyone,

I'm currently working on a mid-70s Sharp Electronic Digital Clock Radio, Model FY-70CH. I found the service manual online, printed it out, and have been studying it for a while. My main reasons for tackling this are: (1) I want to learn electronics and figured I'd start with something I had on hand, and (2) I want to fix its issues. Right now, the radio sounds awful, has about 5V DC at the speaker terminals, and the alarm time setting doesn't work. But I'm not asking how to fix these problems.

Instead, here's what's been bugging me so far:
The schematic for the radio board shows about 40 resistors, all labeled with their values. That's fine. But when I look at the actual radio board, I can only find about 5 resistors. And when I look at the wiring diagram in the service manual (the one that shows the actual board layout, rails, and component placement) I also only see those same few resistors . The parts list at the end of the manual also only includes those resistors (plus of course the ones on the clock board, which I'm not referring to).

However, the wiring diagram (radio board layout) has a blue/cyan overlay that seems to represent all the "missing/ghost" resistors — 30ish of them — the same ones that appear in the schematic.

I'm not sure what to make of this. Are these resistors hidden somewhere? Integrated into something else? Or is there some convention I'm missing?

Apologies if my terminology isn't perfect — I'm still learning. My intro post should give some background on where I'm at.

Attached are some pictures of the aforementioned schematic, diagram and parts list.

I've made the full service manual available here: https://drive.proton.me/urls/TZN4HG59QC#YxX7A8fRFliS

Thanks!