Sharp VC 584UB clock lights up but won't power on

[jmm83]

Bought a Sharp VCR at Savers for $10 but won't turn on
Clock lights up vcr will take a tape
I tried changing the power button but still no luck
I tested and changed some of the caps in the power supply but made no difference
Not sure what else to do
VCR is From 1985 not much info online about it

[Electronic M]

Could be the mode switch is dirty and during power up self testing it rapidly sees that and immediately nopes it's self back into power off.

[jmm83]

I was able to set the timer & make a recording. but after the timer rec is over it still wont power on so i can't play a tape back in it.

[Electronic M]

Does it power on with the remote? Some front panel circuit boards have all buttons going to a single analog line on a control IC and each button pulls down or up through a different value of resistor that the chip senses. If a resistor drifts enough the IC no longer interprets the button it connects to as the function it's supposed to be.

[jmm83]

I didn't get the remote with it but from looking online the original remote doesn't have a power button.
I also noticed the CH buttons don't work either when setting the timer it just says on CH 2

[redk9258]

Originally Posted by Electronic M

Does it power on with the remote? Some front panel circuit boards have all buttons going to a single analog line on a control IC and each button pulls down or up through a different value of resistor that the chip senses. If a resistor drifts enough the IC no longer interprets the button it connects to as the function it's supposed to be.

That is a very good point! Also when the tactile buttons get oxidized, resistance goes high and the control IC misinterprets what button is being pressed. Sometimes if you keep working the buttons, they start making better contact. It's worth a try.

[jmm83]

Tested the resistors on the control panel they seems fine 1k resistors Tested around 995 so I don't think that would be a problem. Not sure what to do now. Maybe the chip on the main board could be bad? Tried a universal remote even though the original one doesn't have a power button but no luck.

[redk9258]

Before condemning the IC, I would check the tact switches for resistance, open and closed. The advise of cleaning the mode switch is a good idea too.

[redk9258]

There's a service manual on eBay for $10.00.

[jmm83]

I tried changing the power button tact switch made no difference, the mode switch is sealed & doesn't look easy to get into without breaking it.
the weird thing is i can make a timer recording with it & it will record to a tape but as soon as you stop the recording the vcr turns off i think that's what it's suppose to do though.

[Blast]

Originally Posted by jmm83

I tried changing the power button tact switch made no difference, the mode switch is sealed & doesn't look easy to get into without breaking it. --snip--

1) To hopefully expand on what redk9258 mentioned, there is likely a voltage going to the power button tact switch that is sinked to ground when said switch pressed. You should be able to probe across the tact switch and look for some change in voltage when it is pressed. If there is no voltage to sink, see how far you can go back to find it.

2) Alcohol will get inside the mode switch. It may not be a complete solution but maybe enough of a procedure to see what, if anything, changes after you induce it.

Good luck!