1990's Fender Prosonic PCB - soldering pads on TOP of PCB?

[Fred G.]

Fender Prosonic question - I have a '90's Fender Prosonic in for a cap job and general "looking over"- looks like the original E-caps are still installed. BIG question - upon opening this thing up, while cleaning pots, tube sockets and switches, I looked over the PCB with my magnifiers and it appears that the two PCBs are TOP SOLDERED with pads on the top of the board! Is this a correct assessment? Can someone enlighten me? I work more on PTP and eyelet board stuff, and all of the PCB gear I work on has all soldering connections to pads on the underside, so I'm a bit unaccustomed to seeing this. Thanks in advance!

Fred G.

[The Dude]

The Prosonic has a double sided circuit board, so there are traces and solder pads on both sides with through holes.

[Fred G.]

Thank you for the prompt answer! I'm going to stupidly pursue this for one more dumb question - I'm assuming that means I can approach installing new components on this PCB in a somewhat similar fashion to the old Fender eyelet board construction, correct? Don't worry, I have just enough experience working PCB's to not f**k it up, I've just not encountered a double-sided PCB before. Thanks for tolerating my question! I appreciate your patience.

[Chuck H]

The high voltage leads are probably PTH (plated through hole). If they look to be soldered from the side you're on then you can probably replace them from that side. Thing is, pcb's are more tender than eyelets so the risk of damage with excessive heat or aggressive work is much greater. To he honest though I've done it enough times to know it usually works out when working from the soldered side. Same rules apply. Suck the joints clean and resolder judiciously. Otherwise blobs can form or even drop from the bottom of plated through holes (causing random and potentially worse problems). Just like eyelets.

[The Dude]

You can install and solder components from the component side. Just a warning: Removing components can be tricky and you MUST BE CAREFUL! Imagine a top hat with a brim on both sides. The circuit board through holes are similar. There is a solder pad on each side of the board. Then inside the board substrate itself there is a conductor "tunnel" that electrically connects the two solder pads side to side. If you rip out that "tunnel" when removing a component, you break the connection from one side of the board to the other side and you have to solder both sides to restore the connection. It's a bit hard to describe, so I hope you can make sense of it. Let us know if not.

Edit: I find it best to CAREFULLY pull out a component lead while the joint is hot molten solder so that you don't pull the through hole conductor out with the component. In other words, remove the component while you are holding the tip of your iron on the joint. Then, after the component lead is removed from the hole, suck the remaining solder out. You also don't want to hold the iron on the solder pad too long or you risk lifting it off the board. You may want to find a double sided scrap board and practice first.

[Fred G.]

Thank you so much, gentlemen!

Trust me, I have enough confidence in my soldering skills to handle this task. But I thank you for the cautionary comments. I've been building, modding, and repairing for 25 years. However, I am NOT formally trained, so my experience is limited to "whatever I come across". This is the first time I've seen a PCB soldered this way. I've done enough modern Fender repairs and FX pedal fixes to be comfortable with PCBs (I hate them, though, lol). Everything PCB I have seen so far is bottom-solderd and requires a bunch of dismantling. Just trying to keep learning.

I'm a retired IT guy ( I can certainly read manuals and I thoroughly understand troubleshooting, lol) who's been gigging for 50 years now (gasp). I started modding my own stuff 25 years ago, began doing builds of my own, and I've gradually morphed into running a repair shop out of my basement. I'm the only game in this small town, so my business is growing and I'm learning on the fly with some of the newer stuff. I can do eyelet board Fenders and PTP in my sleep, but I'm still learning technique on the PCB stuff and it intimidates me a bit.

Thanks for your patience!

[nevetslab]

One more word of caution. Fender has a habit of bending the cut leads over on the bottom side, so heating up the pad from the top won't mechanically release the lead to pull thru, unless it is NOT folded over. I'd have a look at the bottom side of the PCB before unsoldering anything. And, Fender is known for having poor quality PCB's produced. Getting the folded-over leads unsoldered and then lifted up from the bottom solder pad had a tendency to lift the pad right off the PCB material, as well as fracturing the solder pad from the connecting trace. Typical problem on their Hot Rod Series PCB's, as well as Twin and Deluxe Reverb boards, sad to say.

[Jon Snell]

I, without exception, remove the PCB to gain access to the rear, this enables a properly carried out repair as opposed to a possible bodged up job.
Yes, it is not easy to remove a component legs from double sided board, especially if it is not through plated, without desoldering on the pad side. Not desoldering from the leg end of the components can cause problems either straight away or later on, meaning the time you thought you had saved, now means hours on the bench, possibly with an angry customer, fixing yet again the same job that should have been done correctly in the first place.
Most boards come out quite easily, stand offs and pots with the odd jack socket and its out.

My motto, if the job is worth doing, for goodness sake, do it properly.

[mozz]

One more word of caution. Fender has a habit of bending the cut leads over on the bottom side, so heating up the pad from the top won't mechanically release the lead to pull thru, unless it is NOT folded over. I'd have a look at the bottom side of the PCB before unsoldering anything. And, Fender is known for having poor quality PCB's produced. Getting the folded-over leads unsoldered and then lifted up from the bottom solder pad had a tendency to lift the pad right off the PCB material, as well as fracturing the solder pad from the connecting trace. Typical problem on their Hot Rod Series PCB's, as well as Twin and Deluxe Reverb boards, sad to say.

Exactly. If this is the bottom of the board, and you try to unsolder and pull the component out from the top, you are gonna have problems. This is a old Western Electric circuit board, every lead is bent over. As was said, your best bet is to remove the board, clip the bad part out, unsolder from the bottom and pull the remaining lead out. The traces and the plated holes will get damaged unless you have practice on these.

[Greg Robinson]

I agree with Jon and Mozz, not worth the risk of damage, and IMO any apparent "time savings" are a false economy, getting proper access by removing the board might seem like extra work, but it makes everything go much smoother, so you end up wasting less time.

[nosaj]

On the prosonic since the tube sockets are not PCB mounted you will have flying leads going to the pcb. When you remove the Pcb leave leads attached and flip it over. do your thing then reflow all the flying leads on the pcb .
nosaj

[Chuck H]

IIRC (I used to have a Prosonic) all the pertinent capacitors for a "cap job" are on smaller separate boards that have some generous leads. You can probably access the under side of those boards with minimal desoldering of leads. Perhaps none.

[Fred G.]

Any suggestions on removing the bias board so I can replace the e-caps on the board from beneath? To my eyes, I don't see any rational way other than a complete dismantling - I'm finding this exceedly frustrating...

[g1]

Any suggestions on removing the bias board so I can replace the e-caps on the board from beneath?

Does yours look like this?

[Fred G.]

Yes, it looks identical (except in much better condition)! I'm hoping for some tip on flipping the board over enough without having to do a major dismantling effort. I've tried some of the more obvious things, such as clipping off the wire ties, but that just hasn't given me enough access. I don't want to go de-soldering all kinds of leads if I don't need to, but I'm just not visualizing the most effecient way to do this and I figured I'd ask of folks who've been down this path already.