Poor signal on Panasonic DVD Recorder DMR-EX84C

[imwinge]

Hello!

I'm so sad right now, because my beloved Panasonic DMR-EX84C is failing me, despite many hours of replacing each and every electrolytic capacitor inside, an effort now proven to be completely unnecessary. Why then, some might ask, did I bother going through with mentioned procedure in the first place? Well, in order to answer that I must first describe the symptoms my device is displaying:

Digital channels (DVB-C, haven't got a DVB-T antenna so I haven't tried that) have poor signal quality (but high signal strength) resulting in loss of sound and picture.
The same signal appears completely fine on TV connected to the device's antenna loop through jack.
The signal quality is poor no matter what cable I use.
If the device is unpowered for a few hours or more the signal quality is improved, only to become worse again after a day or two.
Analog channels are retrieved as normal.
All other functions are working fine.

There are some threads regarding similar units (in particular the DMR-EX75) that mention that these symptoms are caused by a failing capacitor (680 uF). No such capacitor exists in my unit, and no capacitor looked swollen or appeared to be leaking, so that's why I replace all the capacitors.

Sadly enough, this did not solve the issue, so now I'm turning to you in hope for some other possible solutions, before I admit defeat and upgrade to a blu-ray recorder.

 

[imwinge]

I just realized that I forgot to mention some things that's probably of interest. I've had this problem before.

I had been away for a week and when I came home it had this problem: low signal quality. I didn't suspect the unit at the time, but the antenna or something. The problem went away by itself after a couple of days. Since then I never had an issue.

Until now. And when I think about it – it actually started after unplugging it while testing some other equipment. That's when I decided to "repair" it once and for all, just to find out that the caps weren't the issue here.

I stated in my previous post that leaving it unpowered for a while helps. However, now it seems to be the other way around. After being unpowered overnight the signal went from good to bad. And then after being on for a while the signal got better. Strange.

 

[Gavtech]

I don't know this model. We have never had an equivalent in the UK that will receive cable channels.

However, a very common occurrence which may account for your problems and which is consistent with your description of problems after moving equipment about is HDMI interfence

I'm assuming here that the unit is connected via HDMI - but even if not - if you have other equipment that is, it can be the cause of the problem.

When data passes over the HDMI interlink it can radiate at high frequencies. HD material makes this worse because more high frequencies are generated.

That radiation can be picked up by the incoming UHF aerial lead and those frequencies saturate the tuner and corrupt the wanted signal.

The problem can vary between occasional drop outs when high action scenes occur, to whole wavebands being obliterated.

The remedies for this problem depend on its severity.

Sometimes just moving the HDMI lead as far as possible from the incoming UHF lead can be enough - but that is not always easy.

Trying another HDMI lead is another simple thing to do.
It has been shown that some leads exhibit this problem badly while others do not... and the expense or quality of the cable has nothing to do with it.
You are as likely to succeed with the cheapest replacement.

In bad cases in may be necessary to do all the above and Change the uHF aerial lead to a beefed up well-screened version.

 

[imwinge]

Woho, thanks! That's exactly the kind of troubleshooting tips I was hoping for. Will try removing the HDMI and connecting it through SCART to see if that makes a difference. Thanks!

 

[imwinge]

It seems the HDMI is not what is causing this issue. I couldn't find a SCART cable to connect instead of the HDMI so instead I tested it by

-connecting the optical out of the unit to a receiver so I could hear the sound (which is just garbled noise when the signal is poor)

-disconnecting the HDMI cable and removing it altogether, listening for a difference in sound

The sound was still garbled which means the signal was still poor

 

[imwinge]

I would like to add that there are a few channels that have a better signal quality and can actually be watched. Those channels reside on frequencies from 314 MHz to 338 MHz and have a symbol rate of 6875. All other channels have problem and they are found on frequencies from 346 MHz up and have a symbol rate of 6952.

I don't know if it's the different symbol rate or the frequency that makes the difference in this case, although I'm leaning toward symbol rate.

 

[Gavtech]

I would like to add that there are a few channels that have a better signal quality and can actually be watched. Those channels reside on frequencies from 314 MHz to 338 MHz and have a symbol rate of 6875. All other channels have problem and they are found on frequencies from 346 MHz up and have a symbol rate of 6952.

I don't know if it's the different symbol rate or the frequency that makes the difference in this case, although I'm leaning toward symbol rate.

It is a shame it was not the HDMI problem - which is relatively easy to remedy.

I'm afraid I see the frequency sensitive nature of the problem as likely being an indication of problems within the tuner itself or some of its immediate peripheral support components ( More likely within the tuning can).
It is the kind of problem that can only realistically be addressed usually by substitution.

Any attempt at tampering within the can itself will likely knock the tuning out in any case - plus they are awful to get into and it is usually next to impossible to get detailed circuit data.
They are effectively black box units.

For what its worth I have had a positive result treating such a tuner by carefully resoldering some dry joints.
Care required - Just adding solder can change the tuning.

Sub boards and components can sometimes be had on ebay.
Worth a look perhaps if you want to pursue it further.

 

[imwinge]

I suspected that little can myself, actually, and managed to open it and have a look inside. Unfortunately, I just saw a circuit with lots of micro-tiny components inside, and not one electrolytic cap I might be able to replace. Fortunately though, I saw a French site selling that part. Didn't ship to my country though, but I'll keep an eye on ebay.

For the moment it seems as the signal quality has gotten better so I can watch all the channels, even though I did nothing. Too bad it'll probably get worse again in a while. It would be nice to get rid of the problem entirely.