Hi Gavtech,
Sorry to hijack.
Do you remember my “no freeview on rescan” problem on my DMR ES20? I wonder if it is this same capacitor at fault?
bigmin
Indeed I do. It was my intention to post about this elsewhere to bring it to your attention.
Although not the same model, not surprisingly these units all have similar overall structures as regards the circuitry. So such a capacitor could well be implicated.
As yet I do not have detail of the function of this cap.
If I knew its circuit designation I could deduce it... Unfortunately circuit analysis down to this level virtually does not happen any more in servicing such that I was shocked to discover yesterday, when I looked into this particular capacitor, that Panasonic do not even provide component values in the service manual [ EX75 - I don't have the manual for the ES20 ]... so I could not find the responsible component.
Up to now I've had a working hypothesis of what may be going wrong:
As far as I can tell users have reported that their units apparently scan and find channels as normal - but none are stored, so none are present when the user tries to use a channel.
As far as I know, channel placeholder information is held in an eeprom... which requires
significantly more current to overwrite the information stored in it than in normal routine read operations.
It would be just such a moment that would find a weakness in a supply due to a dodgy smoothing or decoupling cap. I'm guessing that, as the cap cited here is moderately large and is located away from the general PSU area, that it is performing as a decoupling device.
In other words, the information is available, but does not get stored.
There is a flaw in this hypothesis: Why does the old information get erased?
The problem here is I don't have enough information to be certain of the functional operation of this system - so I'm clutching at straws.
The tuner itself has a number of supplies associated with it and this cap could be implicated in any of those... albeit it is a long way from either the tuner or PSU section.
Suffice to say that overstressed caps are just about the commonest cause of failures so it is a strong contender.
It may be that there were software issues also. As I recall you seemed reasonably certain that the scanning problem with your machine with the problem software would always fail on first scan and always succeed on second scan.
If it was truly that reliably predictable, it does call the software into question.