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Start Up Fails When HDD Connected

Hi, it seems I'm the latest to have this fault and thank you to Black Hole for advising me in another post. I have gone through this significant thread with all the information, thank you to newcoppiceman for his original diagnosis work. I am planning to replace the 4u7 capacitor but have not soldered for many years. I do have soldering iron with a small thin bit and I need to buy some solder. I see that care is needed in removing the old capacitor either by desoldering or cutting, is there a preferred method? Also, can the fix be applied with the board in place, or do I need to remove it to apply the fix?
 
Oliver said:
Hi, it seems I'm the latest to have this fault and thank you to Black Hole for advising me in another post. I have gone through this significant thread with all the information, thank you to newcoppiceman for his original diagnosis work. I am planning to replace the 4u7 capacitor but have not soldered for many years. I do have soldering iron with a small thin bit and I need to buy some solder. I see that care is needed in removing the old capacitor either by desoldering or cutting, is there a preferred method? Also, can the fix be applied with the board in place, or do I need to remove it to apply the fix?
Click to expand...
There's a risk of damage to the board with cutting, in particular you may lift tracks - which is really bad news. Provided the soldering iron is intended for electronics work and is 25W min (say 50W max) you would be better desoldering. Some skill is required, but you say you've had some previous soldering experience, so you should be ok. Applying fresh solder will help get the heat into the joints and increases the thermal mass, so aim to work quickly on either side in turn until the cap can be shifted with some light pressure. If you haven't done it within two minutes, stop and try again when things have cooled down (you don't want to overheat the board). You don't need to remove the board, but be careful to keep the iron away from nearby cables connecting to the HDD (maybe shield them with some cardboard). For a really neat job, after removing the cap use desoldering braid (about 3 mm wide) to clean the excess solder from the pads, then a cotton bud dipped in white spirit to remove flux. Good luck.

PS - Don't use a solder-sucker as this can cause tiny fragments of solder to be thrown around with attendant risks of shorts, intermittent faults, etc.

PPS - Get plenty of light on the board while you work on it.
 
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Oliver said:
can the fix be applied with the board in place
Click to expand...
I think that would be tough. Possible, but access is limited.

Oliver said:
I need to buy some solder
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If you can find any, I advise traditional "multicore" tin-lead solder with flux. Much easier to work with than the modern lead-free stuff, and still legal for rework on old equipment. It's almost impossible to use lead-free solder where tools or the workpiece are contaminated with lead, but not the other way around.
 
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Black Hole said:
Much easier to work with than the modern lead-free stuff, and still legal for rework on old equipment (it's impossible to use lead-free solder where tools or the workpiece are contaminated with lead).
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That's interesting, thank you. It's been many decades since I did any soldering and although I still have my soldering iron somewhere from what you say I might need to throw it away and buy a new one? I suspect I need to do some on my HDR-T2 (the fan no longer works but the fan itself is fine, so I'm guessing a capacitor in the power rail for it has gone).
 
Indeed that, and definitely not fading eyesight (!), might explain why soldering appears to be so much harder now. Where might one find proper non-RoHS solder?
 
I have this problem, bought some 4u7 capacitors, and successfully removed the old one and soldered on the replacement. The DVR then rebooted ok!

However I then (very silly) tried to push the capacitor to a neater position, and have pulled one of the pads from the board! This is the connector further from the edge of the board.

So, is there another nearby connected pad that I could connect that leg of the capacitor to instead? using a connecting wire if needed?

Note my DVR is a FOX-T2/RE - the re-engineered blue motherboard, rather than the original green design. Many of the components are moved around from the images on this site. See my image attached. The capacitor I replaced is the one close to the '5'.
 

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pghardy said:
However I then (very silly) tried to push the capacitor to a neater position, and have pulled one of the pads from the board!
Click to expand...
Yes, well...

If you can identify the 10K resistor from the circuit diagram in post 91, tack across that (or the FET pins, if they're easier). Make sure you get the polarity correct.
 
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pghardy said:
However I then (very silly) tried to push the capacitor to a neater position
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Oh yes. The "WTF did I do that?" result. Been there more than once. I think I usually clawed it back eventually, but it was always hard and/or a lot of work.
 
Black Hole said:
Yes, well...

If you can identify the 10K resistor from the circuit diagram in post 91, tack across that (or the FET pins, if they're easier). Make sure you get the polarity correct.
Click to expand...
Any chance you could take my board image and indicate appropriate pads, including polarity? I’m guessing the 10K is the tiny component near the S B on the edge, but is the negative of the capacitor to the S end or the B end?
 
pghardy said:
Any chance you could take my board image and indicate appropriate pads, including polarity?
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No chance at all. Some of the interconnecting PCB tracks are buried inside the board, where no photo will show them. Also, I can't make out any component markings in that snap. To identify which connects to what, you need a "bleeper" (continuity tester / multimeter). Some components might also be on the underside of the board.

pghardy said:
is the negative of the capacitor to the S end or the B end?
Click to expand...
S/B? That seems to imply the pads are horizontal to each other, whereas what I see in that photo is them arranged vertically. Also the cap near the S/B markings is the wrong one (as you said yourself, the 4.7uF cap is near the "5"... if that's the correct 4.7uF cap!).

The negative terminal is marked by the black stripe on the top of the can.
 
I’ve got a multimeter (somewhere) so will have a go. Unfortunately the track I’d most like to trace is the one with the missing pad, so unavailable.

I wasn’t saying the capacitor was near the SB, but what might be the 10K resistor. I had the right polarity for the capacitor (before I broke it), but need to know alternatives to put the negative leg instead of the destroyed pad.

Incidentally I think the components on the blue RE board are largely the same as the green, but relocated nearby.
 
pghardy said:
need to know alternatives to put the negative leg instead of the destroyed pad.
Click to expand...
Look for continuity between pins on two resistors and a FET. The circuit diagram sketch I referred you to provides the clues (the cap is shown with its negative to the left – the line as opposed to the box, which represents the positive terminal).
 
i found what I think is three such linked pads, and have tried using one, but the device remains in the reboot loop. I'm probably giving up at this point. Thank you all for your information and help.
 
Was there ever a consensus on

(i) whether a faulty 4u7 actually needs to be replaced or can simply be removed and not reinstated? There seemed to general agreement it was not needed for a slow start-up but rather for a slow switch-off, but not whether a slow switch off was in fact necessary? I note that prpr (post 254) did not reinstate and had no issues?

(ii) if a new one is required whether it can be any type of cap or has to be electrolytic?
 
Wildebeest said:
if a new one is required whether it can be any type of cap or has to be electrolytic?
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You would never fit a non-electrolytic 4μ7 cap on the board! As to whether you can get away without one, that's a moot point. My view is manufacturers don't waste money on parts not needed.

An alternative approach seems to be to just bypass the 12V switching:
peterpi said:
Job done, but I couldn't change the 4.7uf capacitor. My trusty Weller TCP iron and finest bit work, but I don't trust my seventy plus year old eyes any more, so I did a work around and fed the 12v from a separate supply. A bit of a cheat, but I thought KISS and it does the job. Now to do a backup of the stuff I want to keep and free up some space on the HDD.
Click to expand...
 
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