Dash speaker size/ cb radio location

[Ifitaintbroke]

I'm trying to read this on my phone, but I would say what are the two switches directly above transistor Q501(?) on the left side?

You say "one is a dimmer". What does it dim? The display? An indicator lamp?

They both go to the IC header and switch between direct and through a resistor, it seems.

(again, my eyes are not so good anymore and I'm looking at a sub6" screen)

Circuit boards can definitely fail without scorches.

IC's can fail internally, sometimes a resistor, transistor or diode will fail open without showing on the package.

Often the best way to detect a fault without a logic probe is to look with an infrared camera.

Jim, you are correct. R519 and R520 both go to the switches. I'll have to look up their specified resistance, and check them. I would much rather it be something simple like that. One unit is completely functional, so, if that is the problem, I should be able to take one from the 23, and put it in the 40. Also, can you explain the infrared? What would I be looking for?

[Ifitaintbroke]

I'm trying to read this on my phone, but I would say what are the two switches directly above transistor Q501(?) on the left side?

You say "one is a dimmer". What does it dim? The display? An indicator lamp?

They both go to the IC header and switch between direct and through a resistor, it seems.

(again, my eyes are not so good anymore and I'm looking at a sub6" screen)

Circuit boards can definitely fail without scorches.

IC's can fail internally, sometimes a resistor, transistor or diode will fail open without showing on the package.

Often the best way to detect a fault without a logic probe is to look with an infrared camera.

Looked it up, and, if I'm reading it correctly, they should be 330 ohms. Will test tomorrow.

[ArdWrknTrk]

https://cbtricks.org/radios/royce/1_610/graphics/royce_1_610_om_ser1_sch.jpg

The link is a little clearer but I'm still zoomed WAY in and can only see a fragment at a time on my phone.

S51 & S52 are the dimmers for each of the two digits (7 segment displays, FGABCDE) probably a DPDT* switch.

S14 (to the right of Q501) would pull pin 16 of IC 105 to ground.

I suspect this is what causes channel shift and the displays to change.

[ArdWrknTrk]

Also, can you explain the infrared? What would I be looking for?

With an iR camera you can see hotspots on the board.

Some things (like a resistor that's sinking lots of current) are naturally going to be hot but if you see a hot spot inside an IC or some other component that's overheated it's a good clue there's a failure.

Sometimes you can even feel it with the back of your hand.

I haven't done much troubleshooting at the component level since I was a kid (about when these radios were made)

 

[BigBrother-84]

You mean something like this?

It is Smittybilt's Clinometer app and it provides a wealth of info. I just haven't figured out how to mount the phone somewhere stable yet, but I have a good idea.

https://forum.garysgaragemahal.com/file/n142920/IMG_1061.png

🤣

[Ifitaintbroke]

The link is a little clearer but I'm still zoomed WAY in and can only see a fragment at a time on my phone.

S51 & S52 are the dimmers for each of the two digits (7 segment displays, FGABCDE) probably a DPDT* switch.

S14 (to the right of Q501) would pull pin 16 of IC 105 to ground.

I suspect this is what causes channel shift and the displays to change.

Jim, again, you are correct. S5-1 and s5-2 both go to the dimmer switch. I realize now that each of the mechanical switches are actually 3 switches it the schematic.

[Ifitaintbroke]

Also, can you explain the infrared? What would I be looking for?

With an iR camera you can see hotspots on the board.

Some things (like a resistor that's sinking lots of current) are naturally going to be hot but if you see a hot spot inside an IC or some other component that's overheated it's a good clue there's a failure.

Sometimes you can even feel it with the back of your hand.

I haven't done much troubleshooting at the component level since I was a kid (about when these radios were made)

Another thought. Could it be that the channel switch works, but the display is stuck? I'll have to test it to find out.

[Ifitaintbroke]

Looked it up, and, if I'm reading it correctly, they should be 330 ohms. Will test tomorrow.

Went thru all the trouble to look up and decode the resistors, then realized that the schematic lists the ohm rating right next to the resistors.

[ArdWrknTrk]

Jim, again, you are correct. S5-1 and s5-2 both go to the dimmer switch. I realize now that each of the mechanical switches are actually 3 switches it the schematic.

I think that 5-1 & 5-2 are actually two legs of a single DPDT switch that simply control whether each digit gets a solid ground connection or if it 'sees' 330ohm to ground.

Another thought. Could it be that the channel switch works, but the display is stuck? I'll have to test it to find out.

I don't think that's possible.

IC 501 is controlling which segments of the display digits light up.

It probably cycles through channels with a momentary switch, and outputs to the display on one side and the crystal oscillator on the other.

(M) prefix makes me think Mitsubishi, but I don't have any of my semiconductor books to look up 58804B anymore.

This schematic doesn't follow convention in switch symbols (buttons v/s toggles) but I suspect S4 as that's the only switch that doesn't seem maintained (arrow in lever)

The channel select button on the left is momentary, correct?

 

[ArdWrknTrk]

Went thru all the trouble to look up and decode the resistors, then realized that the schematic lists the ohm rating right next to the resistors.

When I was six I could read resistors at a glance and bin them in my sleep.

Now they're specks the size of coarse ground pepper surface mounted on multilayered boards.

'Times change'...