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 Post subject: PCB Repairs For Dummies
PostPosted: Thu, Feb 01, 2018 5:42pm 
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I picked up a little cheap Jet City Custom 22 about 1 month ago with intentions of doing some mods to it..I purchased the mods and got to work,now I have done some repair work on a Peavey XXX head I had 6 months ago,changed out the Screen Grid Resistors,Channel Switch Relay,the 2 jacks for effects loop and 2 resistors,so I figured I could handle these mods on the JC.
There were 4 mods to do,and instead of doing 1 mod at a time and then plugging in and checking to make sure everything was good,I did all 4 mods,then checked,I ended up with a high pitched squeal on the Crunch channel when I cranked the gain from 5-8,then it stopped until wide open,but I noticed when I switched the Bright switch up and on the squeal is there constantly unless I moved the treble control around,so I was in email contact with the guy who sold me the mods and install info and basically it was check this and that,finally after checking this,adjusting this and that I finally had enough and just wanted to put it back to the original gain structure on both channels and be done with it.
Earlier today I was removing the caps and resistors for the mods and somehow I pulled up a long piece of what looks like a trace,so I stopped and looked underside of board and yeah its one of the wide traces that was in the area,so I went ahead and clipped it,put everything back together and fired the amp up,and the squeal went away,but so did the gain and volume of both channels..I had purchased 2 new soldering irons,a Weller and a Hakko in 30 and 40 watts to do this job because the PCB is so thin I didn't want to take a chance and cook holes in the board,the Weller 40 watt iron sucks,it puts out nothing hardly and the 30 watt Hakko did a better job but it just wouldn't get the job done,so I went with my long used,trusted 60 watt Hakko and the damn pads on top of PCB where the parts are soldered in place cooked,so now I feel I have destroyed the PCB even though I didn't melt or gouge holes in it..also I did a bias pot re-locate mod to the back panel and in order to do that you have to drill the width of the trace out inline with pin 3 of power tubes,that works great but now I don't know what to do..I have seen a few listings for items that are supposed to help repair PCB's but really at this stage I don't know what to do..I just boxed the amp up and took to the big garage outside and said fuck it ! Deep down inside I want to fix this amp,from my description what are the chances I can fix this PCB,and can I solder jumper wires on the traces so I can locate the bias trimpot back on the PCB ? When I did the repairs on the XXX the thicker PCB's could handle the heat,the flimsy ones on this amp allow the pads to lift and dissolve in an instant. any info greatly appreciated !


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PostPosted: Thu, Feb 01, 2018 8:22pm 
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Yeah, I would say run a jumper wire where that tracer lifted up.

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PostPosted: Thu, Feb 01, 2018 9:02pm 
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Loudness250 wrote:
Yeah, I would say run a jumper wire where that tracer lifted up.

Thanks for that info,I have fretted over it,its a cheap little amp but it is one of their newest ones and it sounds pretty damn good,I should have left it alone but I can't help it,I always modify anything I get..well maybe not now. going to try it tomorrow and see what happens.


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PostPosted: Sun, Apr 01, 2018 10:54am 
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Since PCBs are essentially just doing point to point wiring in an easily replicated format

So I ask any amp geeks, Could the Op replicate the schematic for this JEt City using another method...turret board etc?


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PostPosted: Fri, Apr 13, 2018 10:12am 
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if its a short run I usually use a piece of solder wick.works great Especially if I have a short piece thats been used and is full of solder

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PostPosted: Fri, Apr 13, 2018 12:54pm 
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Just use a length of wire to replace the trace. Buss wire works the best since its rigid and holds it form.


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PostPosted: Sun, Apr 15, 2018 1:40pm 
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splatter wrote:
if its a short run I usually use a piece of solder wick.works great Especially if I have a short piece thats been used and is full of solder


Solder wick was never intended to carry any form of current regardless whether it's small signal. Solder wick has solder rosin built into it which when hot, leaks out onto the board. You're asking to short something out by doing this. Solder wick also has thousands of tiny small solder pieces not visible to the eye. These small solder balls could get loose within the circuit and short something out. This is not the correct method.

CrazyNutz wrote:
Just use a length of wire to replace the trace. Buss wire works the best since its rigid and holds it form.


This is the correct method. Leave the trace as is, and run a length of wire rated to the same current and voltage ratings as the trace width you're replacing. Tables exist on the internet for comparison. Run the wire directly over the damaged trace.

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PostPosted: Sat, May 12, 2018 12:24pm 
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I've used this MG Chemicals product to create new conductors. You can get a 1/2 oz bottle off of Amazon. You cannot solder to this, but if the pads are intact, you should be fine.

https://www.mgchemicals.com/products/pr ... -print-843

The amp you are working on was built using lead-free solder. Set the solder iron (Hakko) to 750 degrees for surface mount (SMD), 800 degrees for through-hole (TH). Never leave the tip on the contact point for more than 2 seconds. If you are cleaning the tip with a sponge and water, use distilled water only. This will prevent contamination (lime, calcium) of the solder material. I've mixed lead with lead-free solder with successful results, but you are not going to liquify lead-free solder at 700 degrees; not without causing damage to the board and related components. If using tin/lead solder with lead-free, you will need to increase heat to 750 degrees min.

Hope this helps.


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