Need help determining voltage needed by capacitor

[SocialistCharizard]

Hello,

Today I acquired a Sony HCD-C770 5 disc DVD changer/mini amp that is non-functional. When I power it up, the standby light just flashes repeatedly and the machine refuses to do anything.

Upon checking the internet, I found forum threads discussing a certain electrolytic capacitor that is known to fail and cause this issue. The forum threads referred to capacitor C914 on the power supply board, so I disassembled the machine, found the capacitor in question, and de-soldered it.

My issue is in finding a replacement with the proper voltage, as there seems to be some discrepancies on what voltage capacitor should be used. The forum threads point to either a 47uF 35v capacitor or a 47uF 50v capacitor. Sony's service manual for the HCD-C770 (https://www.manualslib.com/manual/800088/Sony-Hcd-C770.html?page=136#manual) lists C914 as having a max voltage of 50v, which led me to assume the 50v capacitor is the correct one. However, when I removed the cap from the actual machine, I noticed it was actually a 35v cap. This was extremely confusing, as the service manual is telling me the capacitor should have a different voltage than what was actually in the machine.

I then noticed that there were lots of scratches on the inside of the upper case half. This could have been my doing from when I removed it, however, if it was someone else that did this, it would explain why the capacitor voltage was wrong. Someone could have attempted a previous repair on this machine and carelessly put a capacitor with the wrong voltage without consulting the service manual. However, this is also contradicted by how the machine still is able to power up to some extent (as it is essentially giving me a boot time error) and how there is no visible damage anywhere else on the power board or on the capacitor itself. If an electrolytic capacitor with an incorrect voltage was put into the machine, it surely would wreck the power board further or at least produce signs of over-voltage stress on the cap itself.

I'm kind of stuck at this point, as I have multiple contradicting factors here. As of now I have ordered both a 35 and 50 volt replacement capacitor (I got both because of convenience and a low price). I'm just wondering what others think about this, since I'd really like to get this machine up and running. This is also the first time I have actually replaced a component on a board (I've re-soldered wires and de-soldered components before but that's about it), so I want to make sure I'm not going to blow up anything or shock myself due to putting in incorrect components.

 

[Buk]

If you're unsure, use the higher rated, 50V cap. The rating only specifies the maximum voltage it should be subjected to (before the dialetric breaks down). As such, it is always recommended that caps used should be rated higher than the voltage they are destined to see in use. The extra 'headroom' won't affect the circuit's function.

For more, read http://learningaboutelectronics.com/Articles/What-does-the-voltage-rating-on-a-capacitor-mean

 

[SocialistCharizard]

Ah, thank you. I'll try that out once the cap arrives in a couple days and update this thread with the result.

 

[ramondo]

1.Google, capacitor. Several types of caps are available BUT usually you can install a cap with the SAME uf value but can always go higher in voltage. Exp. 47uf@35v replaced with 47uf@50v or 47uf@75v not a problem. The other way around an BOOM.

 

[Nigel Goodwin]

Hello,

Today I acquired a Sony HCD-C770 5 disc DVD changer/mini amp that is non-functional. When I power it up, the standby light just flashes repeatedly and the machine refuses to do anything.

Upon checking the internet, I found forum threads discussing a certain electrolytic capacitor that is known to fail and cause this issue. The forum threads referred to capacitor C914 on the power supply board, so I disassembled the machine, found the capacitor in question, and de-soldered it.

My issue is in finding a replacement with the proper voltage, as there seems to be some discrepancies on what voltage capacitor should be used. The forum threads point to either a 47uF 35v capacitor or a 47uF 50v capacitor. Sony's service manual for the HCD-C770 (https://www.manualslib.com/manual/800088/Sony-Hcd-C770.html?page=136#manual) lists C914 as having a max voltage of 50v, which led me to assume the 50v capacitor is the correct one. However, when I removed the cap from the actual machine, I noticed it was actually a 35v cap. This was extremely confusing, as the service manual is telling me the capacitor should have a different voltage than what was actually in the machine.

I then noticed that there were lots of scratches on the inside of the upper case half. This could have been my doing from when I removed it, however, if it was someone else that did this, it would explain why the capacitor voltage was wrong. Someone could have attempted a previous repair on this machine and carelessly put a capacitor with the wrong voltage without consulting the service manual. However, this is also contradicted by how the machine still is able to power up to some extent (as it is essentially giving me a boot time error) and how there is no visible damage anywhere else on the power board or on the capacitor itself. If an electrolytic capacitor with an incorrect voltage was put into the machine, it surely would wreck the power board further or at least produce signs of over-voltage stress on the cap itself.

I'm kind of stuck at this point, as I have multiple contradicting factors here. As of now I have ordered both a 35 and 50 volt replacement capacitor (I got both because of convenience and a low price). I'm just wondering what others think about this, since I'd really like to get this machine up and running. This is also the first time I have actually replaced a component on a board (I've re-soldered wires and de-soldered components before but that's about it), so I want to make sure I'm not going to blow up anything or shock myself due to putting in incorrect components.

As you've got the service manual, check what voltage rail the capacitor is on - the capacitor just needs to be higher than that - there's nothing 'clever' or 'technical' about capacitor voltages, it's just as simple as that. The value listed on the service manual is simply just what happened to be used the day the schematic was drawn, and often it's down to physical size as much as anything else.

 

[SocialistCharizard]

So, I replaced the capacitor, and the machine indeed powered on. Now, it seems to have an issue reading discs. It takes very long to read a disc, and while it eventually does play without skipping or anything, there is obviously something wrong here.

I'm guessing that it is the laser mech, but I need to investigate further to confirm.

 

[SocialistCharizard]

A little update on the machine's behavior:

I opened it up to see how the system was acting while reading, and it appears to spin up, then give up and spin down, then spin up again in a cycle. It even does this with a blank DVD+R that should appear as "NO DISC".

 

[rjenkinsgb]

You coudl try cleaning the pickup lens? A lens cleaner disc or very! carefully with a glasses cloth and as near no pressure as possible.
They can accumulate a film of dirt over time, that causes problems.

Other than that, it could be the laser failing - they can get weaker over time & eventually stop reading properly.

 

[Nigel Goodwin]

Just a little more info on 'cleaning' - it's worth a try, a cotton bud and IPA is the usual technique, and gently clean the lens.

However, all you're cleaning is one side of the lens, not the laser, and not the optics - all of which also get dirty. But it's worth a try, and may give enough improvement for the unit to work for a while longer.

This is why manufacturers don't suggest cleaning, and always suggest replacement.

 

[SocialistCharizard]

I will see if cleaning does anything. It seems to be fluctuating between flawless reading and endlessly trying. It is almost as if the laser is dead half the time and alive the other half. Definitely mysterious behavior. If the laser mech does need replacement in the end, I will most likely trash the machine, as the laser mech doesn't seem to be available at a decent price on the internet. It was in the end a thrift store find, and the particular thrift store I got it from has multiple other DVD changers available. This particular machine is also a rather poor DVD changer, as it takes forever to change discs (maybe a worthy trade off for some, since it is not much larger than a single disc DVD player due to it's compact switching mechanism, but I'm not particularly concerned with the size).

 

[SocialistCharizard]

While removing the disc insertion mechanism (it's an odd slot loader) to get access to the lens, the PCB holding a sensor for the disc grab rails cracked in half, which causes it to not take in any discs. At this point I have decided to throw away the device. I appreciate everyone's help here and for bearing with a repair newbie such as myself.