When I power on the tuner, the display is partially illuminated and there is no response to any buttons being pressed on the tuner or on the remote control. I've included a photos of the tuner and what the display looks like. I'd appreciate any help to fix this, thanks.
Google Photos
Google Photos
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It looks like the microprocessor/controller is locked up. There could be multiple reasons for this and troubleshooting can be difficult.
Try first, unplugging the unit for a couple of hours and see what happens when you turn it back on... do the symptoms change?
Try first, unplugging the unit for a couple of hours and see what happens when you turn it back on... do the symptoms change?
Service manual is here, several problem fixes are mentioned.
Don't see a battery inside, so let it sit overnight.
Sony ST-V77 - Manual - AM/FM System Control Tuner - HiFi Engine
Don't see a battery inside, so let it sit overnight.
Sony ST-V77 - Manual - AM/FM System Control Tuner - HiFi Engine
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Unplug the tuner from power and try it again in 12-24 hours.
Did you have any power line disturbance or storm recently?
Did you have any power line disturbance or storm recently?
The service manual talks about poor contact between 2 parts of the R shield that can cause the remote control reveiver section to oscillate and block key functions
There's probably digital power as some of the 7-segment display lights up, but perhaps the clock for the µController is kaput? Or the digital power isn't stable. Or the firmware has faded.
First to check is power supply voltages and that all connectors are properly seated (including any socketed ICs).
First to check is power supply voltages and that all connectors are properly seated (including any socketed ICs).
There may be no battery (haven't looked at the manual) but there is often a 'supercap' to retain a 5 volt supply. If there is, and if you try discharging it then I would use something like a 220 ohm resistor and leave it connected for several hours.
Stuck 'frog' switches as we used to call them (tact switches on the panel) can inhibit the uP if one is stuck or leaky/shorted.
Final resort is discharging the backup cap (if it has one) and ensuring ALL supplies are discharged and then shorting ALL pins of the uP using aluminium foil. Press it hard onto the pads to short them all out... this helps remove the last remnants of residual charge that may be causing the logic to latch.
If all that fails then its time to get the scope out and go around ALL pins of the uP looking to see if anything looks amiss.
Stuck 'frog' switches as we used to call them (tact switches on the panel) can inhibit the uP if one is stuck or leaky/shorted.
Final resort is discharging the backup cap (if it has one) and ensuring ALL supplies are discharged and then shorting ALL pins of the uP using aluminium foil. Press it hard onto the pads to short them all out... this helps remove the last remnants of residual charge that may be causing the logic to latch.
If all that fails then its time to get the scope out and go around ALL pins of the uP looking to see if anything looks amiss.
Did you unplug it from the wall?
Many of these devices are never truly off unless unplugged and in some situations are only reset when plugged back in.
I powered it on again after 18 hours. Still the same. I had unplugged it from the wall socket overnight. There is a CR-2025 battery soldered to the PCB
When the µP is not coming up, often a dead electrolytic in the vicinity is the culprit (e.g. in the reset circuitry). That said, a dead or half-dead backup battery can also wreak havoc.
Should I try replacing the battery with one of these?
CR2025 Tabbed Battery For Pokemon Replacement GBA / SP | eBay
CR2025 Tabbed Battery For Pokemon Replacement GBA / SP | eBay
Take the battery out and then short the battery terminals on the board for a little while to remove charge. Then see if it works without the battery fitted. The battery is only to retain settings.
And as Rayma and Douglas mentioned earlier MAKE SURE YOU UNPLUG IT FIRST 🙂
And as Rayma and Douglas mentioned earlier MAKE SURE YOU UNPLUG IT FIRST 🙂
I removed the battery and shorted the terminals. I powered the tuner on and it's still the same
Hmmm... so its looking more of a deep seated issue unfortunately. I wouldn't like to guess from this point in, I would be looking with a scope now to check all around the uP noting anything unusual.
Although you can't tell good data from bad data on a scope, we would be looking for 'expected' results such as clean logic swings between the appropriate levels and so on. Sometimes something like a bad memory chip (I'm sorry I haven't looked at the manual for this tuner) can pull a data line down... it really could be anything at this point... but a scope would be my next step if I had it on the bench.
Although you can't tell good data from bad data on a scope, we would be looking for 'expected' results such as clean logic swings between the appropriate levels and so on. Sometimes something like a bad memory chip (I'm sorry I haven't looked at the manual for this tuner) can pull a data line down... it really could be anything at this point... but a scope would be my next step if I had it on the bench.
Now the tuner won't power on from standby. I hear the relay click when pressing the standby button on and off, but the standby light remains on and no display lumination.
All you have done as far as we know is remove the standby battery and at that point the symptoms were the same...
If you left the unit off for while, then what you are seeing now is in a way typical of a logic related issue. There is no battery backup to retain the logic in whatever state (corrupt or otherwise) that it was in and it may well have 'reset' to another state.
I would be tempted to try what I mentioned earlier and that is to short the uP out with tinfoil (but make sure it is unplugged first and that all rails are discharged).
Also and again, this is where you really should make real measurements (scope and DVM) and try and see why it behaving as it is.
First steps are ALWAYS to check all supplies both with a DVM and then a scope to make sure they are clean.
Check the oscillator (clock for the uP) is running.
Check the reset line to the uP is correct.
Check that there is no stuck input data (from panel switches etc) to the input ports of the uP.
If you left the unit off for while, then what you are seeing now is in a way typical of a logic related issue. There is no battery backup to retain the logic in whatever state (corrupt or otherwise) that it was in and it may well have 'reset' to another state.
I would be tempted to try what I mentioned earlier and that is to short the uP out with tinfoil (but make sure it is unplugged first and that all rails are discharged).
Also and again, this is where you really should make real measurements (scope and DVM) and try and see why it behaving as it is.
First steps are ALWAYS to check all supplies both with a DVM and then a scope to make sure they are clean.
Check the oscillator (clock for the uP) is running.
Check the reset line to the uP is correct.
Check that there is no stuck input data (from panel switches etc) to the input ports of the uP.
uP is the micro-processor, the big chip which usually (not always... but usually) is not to blame for faults like this. As a general rule they are extremely reliable. Only when we have measured around all the pins and looked at logic levels and so on would we even consider pointing the finger at such a chip.