Cambridge audio 640a amp has intermittent operation of the standby / on switch. Remote control turns it on & off every time. But using the switch on the front, it pulses the input light on off and can hear kind of relay switching noise. I used to be a tv engineer so i can change parts if i need to. Looking at the service manual both the manual switch and the IR receiver seem to go into the same device in separate pins but i don't know what this does. Manual says U5 PIC16C57, but may be a dry joint. Looking for help any any advice.
PIC16C57 is a micro-controller.
PIC16C57 - Microcontrollers and Processors
Similar to an Atmel AVR or Chinese STC.
I bet Your problem lies in the switch. Probably it is debouncing.
Switch Debouncing - The Lab Book Pages
I would try some deoxit first.
I had success with a small say 100nF ceramic cap across them used in disco lighting gear like DMX channel up-down & enter switches.
Check PSU Voltages feeding the PIC. Noisy rails caused by bad caps can cause havoc on micro-controllers.
The problem is.. If the micro-controller is bad and if You need to change it, You'll have to ask Cambridge Audio for the firmware and a mean to program it.
PIC16C57 - Microcontrollers and Processors
Similar to an Atmel AVR or Chinese STC.
I bet Your problem lies in the switch. Probably it is debouncing.
Switch Debouncing - The Lab Book Pages
I would try some deoxit first.
I had success with a small say 100nF ceramic cap across them used in disco lighting gear like DMX channel up-down & enter switches.
Check PSU Voltages feeding the PIC. Noisy rails caused by bad caps can cause havoc on micro-controllers.
The problem is.. If the micro-controller is bad and if You need to change it, You'll have to ask Cambridge Audio for the firmware and a mean to program it.
The front panel switch is a PCB mount tactile type.
1825910-6 | Black Button Tactile Switch, Single Pole Single Throw (SPST) 50 mA @ 24 V dc 1.4mm | RS Components
If you unscrew the small PCB holding it in place you can check the height of the switch,RS do a full range.
This fault is common where the Amplifier has had good usage.
1825910-6 | Black Button Tactile Switch, Single Pole Single Throw (SPST) 50 mA @ 24 V dc 1.4mm | RS Components
If you unscrew the small PCB holding it in place you can check the height of the switch,RS do a full range.
This fault is common where the Amplifier has had good usage.
Thanks MAACO and Audio Service, both correct is was indeed the switch, soldered in a new one and now all good, needing a standard Torx T8 for the lid through me.part from RS 4791413 had to buy 20 as min order
Actually, I'm sure the switch is probably just a little worn but perfectly OK. The real problem lies in the Cambridge Audio software debounce routine which clearly only works with 'new' switches. The debounce period is insufficient.