Power Supply Caps Replacement (Blues Deluxe)

[NGW]

Hi TUT Team,

I have a Blues Deluxe on the bench which needs some attention, including replacing the leaky IC brand HT filter caps.
I have replaced quite a few IC caps in the past, on Fender Hot Rod series amps, using better quality caps.

This amp dates from the mid-'90s and I am wondering whether I should replace the filter caps for the 16V SS supply (C38, 39, 43, 44) and the Bias supply (C37, 40) also.
The reason I ask is; with the flimsy PCB traces and the difficulty removing the solder from these flush mounted radial caps, without damaging the traces, I don't want to add to the cost to the owner and the aggravation to me if they don't usually give trouble. 
I haven't seen any problems with them in the past, but due to the age of this amp, maybe I should persevere and replace them.

Have any of you blokes had problems with these caps, or do you recommend replacing them anyway?

Cheers, Noel.

[K O'Connor]

Hi Noel

The service life for an electrolytic is generally regarded to be about fourteen years maximum, based on the changes of dielectric absorption (DA) and dissipation factor (DF). This is regardless of whether the cap is long-life and/or is operated at much reduced temperature and/or how the life calculation might come out, with a result longer than fourteen years.

Apart from that, as you describe these amps are not easy to work on - a "fix" might result in a few "breaks" that then need fixing themselves. So it is a tough decision. The old adage "if it ain't broke don't fix it" seems to apply, but if the unit fails soon after you've repaired it, the customer will think you did a poor job regardless of the fact that a completely different thing failed each time.

If the amp is played regularly then the caps will remain functional for decades even with astronomical DA or DF. The mechanical integrity to the board is important if these are axial-lead.

Note that the removal of a component from the board should be done in a manner that saves the board rather than the component - unless the part is extremely expensive or cannot be obtained or substituted. Always ADD fresh solder and remove the component with live heat THEN clear the holes. Trying to clear the holes first results in far more heat being used and potential lifting of traces or pads. ALWAYS ADD fresh solder when you are doing the solder removal step with a solder sucker or wick.

I'm not sure if any of this helps with your decision? But everyone should heed the advice of the "note".

[makinrose]

I'd done a number of cap jobs on these in last few years. They can be done successfully but they are tricky to work on.


Kevin's point about: " Note that the removal of a component from the board should be done in a manner that saves the board rather than the component". Is a really good one as is the advise about how to remove the parts. I learned the hard way!

When do these I clip the leads the axial cap both beneath the board and close to the cap before trying to remove them. You want to only be pulling out short straight piece of wire or you'll damage the pads. It's very delicate board.

My other recommendation is to pay special attention to the 470 ohm 5W resistors in the power supply for the relays. They often need replacement or at the least to have the solder joints touched up. I've seen lots of these where they fail.

Good Luck!