ge space saver clock radio (time wont change)

[CoopedUp]

I have a clock radio that my grandma gave me to fix. the radio didn't work for a while and I fixed that but the clock recently stopped working as in the clock time doesn't change it stays at what its set too. it has the tms3450nl. I replaced the caps on it but that didn't do anything. all of the other features seem to work but I can't figure out what it could be. the clock input which is low voltage ac is present as well.

[Renate]

Well, since it's battery backed up, it shouldn't actually need the AC line to tick off the time.
If the set buttons make things change at the appropriate rate then your clock input is fine.
Maybe the "Alarm Set" button is shorted and you've been looking at the alarm time all the time?
(Or does the "Alarm Set" button correctly switch to a different time.)

[CoopedUp]

this one isn't battery backed but that very well could be the case... I should have thought of that

[CoopedUp]

so the timer works... just figured that one out. I don't think there's actually an alarm on this thing, I know the chip allows for one but there's no way to set one

[CoopedUp]

I think I found the problem... There's a diode for the alarm signal and as you mentioned I was staring at the alarm time... but there's still no way to set an alarm on the clock

[CoopedUp]

the diode seems to have fixed the problem... it works!!! yay now I can give it back to my grandma

[CoopedUp]

well, it looks like it is having problems again... IDK if that's the diode that I replaced or the switch.

[Renate]

Do you have the schematic or a model number?

Do the set buttons make the numbers change  correctly?
Does the colon blink?

I mean, there's really not a lot to a clock using this chip.

Ah, I see, this has a timer mode for baking instead of the normal alarm?
Is there an indicator for time vs timer?

There probably are one or two (small, signal) diodes around the buttons to make the timer modes work.
Can you make the alarm squawk?
Is there a 110k resistor in there?

[CoopedUp]

it has an outlet that you can set up to turn on at a time in the day, its called auto. there's an auto set and an auto enable so two switched and if you turn the auto enable past auto enable to timer which is just an hour on and then back to off I see the actual time for a bit before it goes back to the "alarm" time

[CoopedUp]

I'm fairly certain a switch is the problem because if I turn it with my tongue at the right angle I can display the proper time

[CoopedUp]

The switch you can see in this picture is inbetween two positions and is allowing the clock to function properly. I tried cleaning the switch with contact cleaner to no avail
 

[Renate]

Yeah, that's a 3 position slide switch.
There are two different styles of this.
You can tell the difference by the layout of the pins on the back.
In either case, it's either single pole or double pole.

If there are 4 pins (or two rows of 4) with the four pins spaced equally:

Code: [Select]

  A   B   C   D    (A&B are shorted)
  ^---^

  A   B   C   D    (B&C are shorted)
      ^---^

  A   B   C   D    (C&D are shorted)
          ^---^

If the pins are spaced unevenly it is more likely a normal common and three selections.

These slide switches wear out over time, the little tabs on the bottom that hold the pieces loosen and the pressure on the contacts decreases.
If you can identify and replace the switch, that's one thing.
You could remove the switch, either open it up and clean it (or not) and press the little metal tabs with pliers to hold the pieces together more tightly.
If you don't need the options of that switch, you could also replace it with jumpers.
Of course, replacing it would be the thing.

[CoopedUp]

I dismantled the switch and cleaned it put it back on and it still doesn't work... the signal diode isn't getting pulled low unless the switch is in a weird spot. the switch has 5 pairs of pins a group of 6 and group of 4. im guessing the slide on the contacts is bridging the right contacts but barely and in the wrong spot.

[Renate]

Oh! That's a 4 position switch.
https://www.ebay.com/itm/5Pcs-4-Position-10P-2P4T-Panel-Mount-Micro-Slide-Switch-Latching-Power-Switch/323744748229

[CoopedUp]

yea I guess it would be that. I dont think the switch is at fault here... there is some other problem

[Renate]

Well, you need to do some sleuthing here then.
First, what are the four positions of that switch? (Clock, timer, sleep, seconds, whatever).
When you can fudge it into showing the clock where is the switch? (Halfway between ? and ?).
Did you try the clock while the switch had been removed?
Open circuit everything should get you clock (unless they use a transistor to invert something).

Pin 20 on the chip is VDD, which would normally be something positive, but this is PMOS so it's more the negative side.
Use this (or trace out a handier place with an ohmmeter) as your black on your DVM
Check pin 19 (Alarm Disp), it should show no real voltage.
Check pin 23 (Sleep Input), it should show no real voltage.
This would be the setting for clock.
Trace out 19 & 23 to your switch.
Figure out what is going on.

[CoopedUp]

I still get alarm when I pull the switch out... so it must be a transistor or something that's bad somewhere

[CoopedUp]

After a while of goofing around with it, I realized that I had made the mistake of thinking a different switch wasnt at fault even though it was the problem... after cleaning it a bit I saw the actual time but I couldn't change it, after more cleaning I could kinda change the time and after I took it apart I lost the ball detent and then made my own and put it back together and boom it works for now... Yay?