Mercury Epiphone Valve Junior - Tips for Working on PCBs; Repairing Damaged Eyelets; Revealing Traces; PCB Trace Repair Methods

40 Epiphone Valve Jr.•Mercury Upgrade Kit
ThisprojectanditsdocumentationistheresultoftechnicalinvestigationsmadebytheengineeringstaffofMercury Magnetics.Thedisclosureoftheinformationhereinmaypertaintoproprietaryrightsand
thefurnishingofthesedocumentsdoesnotconstituteanexpresedorimpliedlicensetousesuchmaterials.
Tips ’n Tricks for
Working on PCBs
APCB(printedcircuitboard)beginslifeasasolid
sheetofthincopperfoilacrossabackingmaterial
madeofepoxyresin.Then,usingaphotographic
process,acircuitisimprintedontothefoiland
allunnecessarycopperisetchedaway.What’s
leftarecopperfoil“traces”thattaketheplaceof
wires.Topreventshorts,PCBsarelaminatedwith
acoloredinsulatingmaterialthatfunctionsjustlike
theshieldingaroundinsulatedwire.AlthoughPCBs
maybemanylayersthick,thePCBusedinthe
thisampissingle-layered,whichmakesiteasierto
workonormodify.
PCBscostsubstantiallylesstoproducethantheir
predecessors,i.e.point-to-pointcircuitboards.
Andareusedbyampmanufacturerstomaintain
affordablepricesforconsumers.
OnaPCBcomponentsareoftenattachedtothe
topoftheboardandthensolderedfromtheback
viapass-throughconductive“eyelets”wherethey
followthetracesthatmakeupthecircuit.
Asian-madePCBsaretypicallynotasresilientas
thosemadeinthewest.Thereforethey’relikelyto
Continued on next page è
Damaged
eyelet
Intact
eyelet
Repair to a damaged eyelet:Theleadfromcomponentbypass-
esthedamagedeyeletandissolderedtoeitherarevealedtrace
oranotherterminalonthesametrace(asinthisexample).
Various examples:1.Jumper.2.Jumper.3.Tracerepair
(jumpersolderedfromterminaltoterminalonsametrace).4.
Tracerepair(ditto).5.Damagedeyeletrepair(leadissolderedto
arevealedtrace).
1
2
3
4
5
requirepatchingandrepairworkasyoumakethe
Upgrade.Thisisnormal,andeasytodo–aslong
asyouknowafewtricks.
Revealing a Trace:Sometimesweneedto“reveal”
tracessothatthePCBcanbemodiedorrepaired.
Aneasywaytodothisistotakeasharpknifeor
Exactoandcarefullyscrapeawaythelamination
to“reveal”thecopperfoilunderit.Usehigh-grade
(99%)IsopropylalcoholandaQ-tiptocleanthese
newcontactsbeforesolderingtothem.
How to Repair Damaged Eyelets:ThePCB’s
conductiveeyeletsareeasilydamagedand