Help with DC on volume pot

[mkusan]

Originally Posted by hitachi_nut

Not surprised with the result at all. I already brought up the capacitor leakage issue on posts #76 and #84.

Hi hitachi_nut,
yes you were the first who suggested capacitor leakage issue and for that you deserve all credit and my gratitude.

My only fear is that not only caps are the culprits here. Only reason for me thinking that way is because the amp was silent for more then six months after recapping, if the caps were leaking wouldn't they leak from beginning, such was the case with C517, it leaked the most when freshly installed.

Anyways, per your recommendation I ordered Panasonic caps ECQV1 in 1uF/63V value so we can exchange C505/C506 and C527/C528, I recall you mentioned they are small in size, do you perhaps know exactly how small, those MKT were a tight fit so just to know what to expect when Panasonics arrive.

[mkusan]

My wife informed me that the Panasonic caps finally arrived, contrary to my expectations they arrived last although the were ordered first. That is life

My wife was also kind enough to send me this picture, I am at work, so in preparation to install them I have a few questions. From the picture it looks like lead space is pretty wide, Mooly you suggested drilling the pcb instead of bending the leads. Since I have never done such a thing I practiced a little on some pcb pictured below. I understand I should expose bare copper but how do I improvise the "eyelet", soldering post that is. Track in the picture is pretty wide so "eyelet" in this case is probably unnecessary, but I presume that the tracks in my amplifier are probably thinner. Inputs very welcomed here.

[AndrewT]

Gently scrape off the coating over the copper strip.
Apply a hot iron and cored solder to the freshly cleaned copper surface to thinly tin the strip with the holes.

Insert the legged components from the other side.

Solder each components leg to it's respective strip (pad).

[mkusan]

Originally Posted by AndrewT

Gently scrape off the coating over the copper strip.
Apply a hot iron and cored solder to the freshly cleaned copper surface to thinly tin the strip with the holes.

Insert the legged components from the other side.

Solder each components leg to it's respective strip (pad).

Hi AndrewT,
and thanks for quick reply. So I should carefully tin around the hole before inserting the cap? One more, I presume I can but just to be sure, can I use one original existing hole and add another, new one which is drilled further apart then the second original hole? It is a complicated sentence but I think you will understand what I mean.

[AndrewT]

your newly drilled holes are quite close together. Just tin the whole strip. Don't try to create a tinned pad around each hole.

If you had a single isolated hole, then it is worth exposing a small clean copper area to create a single pad.

Soldering the pad areas (strip) before you attempt to attach the components will make the attachment much easier and less likely to damage the components and less likely to damage the glue joint from copper to substrate.

[Mooly]

The green solder resist just scrapes off. Try a sharp craft knife.

If the tracks in the amp are very thin then to avoid damage drill the hole next to the track without actually drilling into the copper. Then scrape the resist from the track alongside and insert the component lead and bend it to the newly cleaned track and solder.

[mkusan]

Thank you both for your advices.

Seems doable and hopefully I will report here tomorrow that C505/C506 and C527/C528 has been changed to Panasonics so we can continue debugging this amp. I sincerely hope this is the end of LN cap replacement

[Mooly]

Originally Posted by mkusan

I sincerely hope this is the end of LN cap replacement

Your not the only one

[mkusan]

Originally Posted by Mooly

Your not the only one

Just in case with those wimas I also ordered some tantalums 3,3uf for C545,C546 position, if the need arise they are at hand.

[mkusan]

The caps were a lot smaller in person then the picture suggested and the color of them is such that they blended perfectly in the Rotel interior, thanks for recommendation hitachi_nut, unfortunately same can not be said for those light green MKT caps, see pictures.

I drilled new holes the for leads and that went smoothly, although I would like to add one more advice to those already made by AndrewT and Mooly, and that is to check for any resistor crossing the track to be drilled on the top side, I was lucky

To summarize C505/506 and C527/C528 have been changed to Panasonic ECQV 1uF, C517/C518 to ERO VISHAY MKT1826 4.7uF. Everything that was unsoldered before for testing purposes is soldered back, except of course volume pot and C505 and C506 are still tied to ground via point E7.

Is it (tea) pot time now?