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What's up with my old satellite receiver?

You might recall my old Comag/Silvercrest SL-65 started to act, shall we say, erratically. That's why (and many thanks to Mick) I have a replacement digital receiver with a pretty poor user interface, but it works.
  • I can't use either of the two Sky Digiboxes, nor the FreeSat box, because none of these support (by design) the DiSEqC system used for satellite switching. I use dual feeds for NHK World, arte, TV5, and so on.

I needed to realign my dish, and I discovered that no signal is fine (though no LNB will render the receiver unable to switch on), and a good signal is fine, but a weak/iffy signal is what causes the trouble. As the newer receiver, nor any of the others, include a signal strength beeper, I needed to use the SL-65 for tuning. Lovely. It was possible, just.

Poking around with my meter, there are three feeds. A +24V feed, a +9V feed, and a +3.3V feed. I measured the +24V running a little under at +22.6V. The +9V is a little over at +9.31V. And the critical, for this will no doubt be running all of the processor/DSP/memory is the +3.3V. This is the one that is the most important, and possibly the one that the power supply is locked to keep stable. It measures between +2.94V and +3.00V. That's possibly dangerously low, so much so that if extra processing has to be done (say, enhanced error correction for a poor signal), it will load the power supply too much, the system will fail, and the watchdog will kick the system - hence the restart activity that we see.

Here's a video. It is in HD (if your system is up to it) plus has English language captions for the hard-of-hearing or people that don't understand my Brit accent... ☺

As I said, I suspect this is a failed capacitor. The interesting question is is this a failure due to Capacitor Plague, or simply age? The lifespan of a capacitor is between five and ten years, depending on numerous factors. The SL-65 has been in service pretty much since I received it. When was that? 2006ish? We'd hope that a domestic device would manage a little longer than five or six years, but then given that the entire thing cost the same as three maxi-size McDonald's meals, I figure that they probably selected less expensive components, and a shorter shelf life is the price we pay. Or maybe after the Capacitor Plague, ripple effects are being seen all around (it seems a fair few techies have rejuvinated equipment with a PSU repair kit that is basically a bag of replacement capacitors).
Comag SL-65 power supply module
While the big brown capacitor on the left ("QC OK") is slightly bulgy, my money is on the tall capacitor at the upper right of the picture, next to the big diode. This one looks and feels quite bulged, and perhaps it is this that is throwing things off enough that the PSU isn't capable of providing a good 3.3V supply?

I dunno.

I guess if/when I have the cash together for my Farnell order for the JTAG bits (no, I haven't forgotten!), I'll add in some capacitors. Mmmm, 680µF, 16V. No idea what the ESR (etc) is, nor the tolerances. I picked one based purely upon the fact that it had the longest rated lifetime (a mere 8000 hours at 105°C!). Here's the Farnell product page. Got to order in quantities of five, but that only runs to €2,10. I probably ought to measure, make sure replacements would actually fit... But... not today...


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joe, 14th March 2012, 12:16
Hi Rick, 
I have got an ARM JTAG Wiggler, which I have purchased about one year ago, with the intention to help someone to un-brick an ARM device, at the end the person disappeared from the face of our planet and we couldn't find any pin-outs how to connect the device. 
The ARM device was a HP ipaq 312 with ARM 1136 and the JTAG is from this guy: 
Product name: Low-cost Wiggler ARM JTAG adapter Programmer Debugger, if you follow the link, you would find more information about it. 
The most important thing, you can have it for free. 
Rick, 14th March 2012, 20:00
Hi, Rick, 
Took long enough to find you folks. Tell Mum happy birthday and force her to email me. 
Your uncle

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