Cobra 2000 On/Off button diagnosis help

[SteveSteve]

Hi all
Yesterday pwr button on Cobra quit working properly. It no longer shuts radio off, now when pushing the button, all lights dim, receive noise drops a little and it goes freq display to the clock display, but the radio does not shut down
I run the radio from a separate pwr supply as I have always found the radio to be more stable that way. So right now I can turn radio on and off by turning separate pwr supply on and off

So is it safe to assume the on/off switch in the cobra is the culprit and needs replacing?
Thanks for the help

 

[Holydvr]

I do believe the switch is no good.

 

[Shadetree Mechanic]

Check the clock settings. I believe that the clock can turn the radio on by itself without the power switch.

 

[Handy Andy]

Check your rear panel AC/DC (External power) switch

- then look inside that radio where that switch is, make sure all the wires show continuity
- (a continuity point to point check) for proper point to point wiring.

This symptom - it can mean the AC/DC switch or the diode protection (one way wiring) is damaged.

​

The AC/DC switch - being a dual pole type - might be getting flakey - high current demands on this switch - like a shorted final - can cause this switch to deform. The heat on the plastic innards - can make a mess of the contacts it's supposed to bypass in AC or DC modes.

It also uses a diode D402 - by the power supply wiring harness - that if pushed with a lot of current - backwards or due to demand - the diode can blow shorted - then the power supply is "fighting" itself.

 

[guitar_199]

HA.... is that AC supply ALWAYS ON when plugged in??????
I am guessing so since I don't see a power switch in this snippet.

I don't know why....but things like that make me itch.

[[edited later to add]]
* sigh * I just went and looked at the manual on my SBE Console V. It does the same thing. And IT doesn't even have a clock for an excuse!!!!!!!!

Check your rear panel AC/DC (External power) switch

- then look inside that radio where that switch is, make sure all the wires show continuity
- (a continuity point to point check) for proper point to point wiring.

This symptom - it can mean the AC/DC switch or the diode protection (one way wiring) is damaged.

View attachment 44197​

The AC/DC switch - being a dual pole type - might be getting flakey - high current demands on this switch - like a shorted final - can cause this switch to deform. The heat on the plastic innards - can make a mess of the contacts it's supposed to bypass in AC or DC modes.

It also uses a diode D402 - by the power supply wiring harness - that if pushed with a lot of current - backwards or due to demand - the diode can blow shorted - then the power supply is "fighting" itself.

 

[Handy Andy]

@guitar_199 - it's not the only one, MANY Unidens (The Pro-810/710 series, Even the Madison too - gotta' check me on that) base radios' do the same thing - they LIFT the ground return, shuts off the radio - but if you "bond" the chassis and install a grounded cord, the Neutral/Ground bonding back at the Breaker box will NOT shut off the radio completely - the low resistance of the ground loop return is enough to keep the radio powered.

On my own equipment - I had to remove a grounded power filter jack (like those used on the older CRT monitor) that fits power cords like ones used with PC-AT/XT's for the Pro-810e I own.

@SteveSteve - that brings up another potential problem (literal sense and result) - did you have work done to bond the back panel and case to the same ground that your power outlet uses? If so, you might want to investigate that, it can explain why the radio is not shutting off. Because Ground for the Foil Board ground the radio has, can be made the same ground the power outlet uses - and generates a ground loop problem.

The normal power switch, "lifting" the power supply ground may not interrupt the power - for ground that the same transformer/power supply can use as a Neutral/Ground "lift" is (can be) maintained and kept alive by the radios OWN Foil Board Ground, Case Ground and Power Outlet Ground.

They can be tied together inadvertently - nothing special - just be aware that to turn off the radio in these situations - requires the POWER Cord to the RADIO to be unplugged.

 

[nomadradio]

At the very rear of the counter/clock module is the power connector for that module. Make sure the AC cord is unplugged, and pull off that plug.

I'm pretty sure that's where the clock's alarm feature connects to the front-panel power switch. A device called a SCR inside the module is triggered by the clock's alarm output for a 'wake to radio' feature. If that part goes bad, the radio may only partly turn off. If pulling that plug makes the power button function fully again, this is what's going on.

And if it makes no difference, blame the switch.

73

 

[guitar_199]

I'm just showing my age......

I miss the "old days" when OFF meant... "NO ELECTRONS WERE MOVING"