Sony ST-V77L Tuner 'Frozen'

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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 :)
 

humanoid85

Member
2018-04-26 11:03 am
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 :)


I removed the battery and shorted the terminals. I powered the tuner on and it's still the same
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 

humanoid85

Member
2018-04-26 11:03 am
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.


I don't know much about electronics. What is the uP?
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.