Service manual

Page 4
TROUBLESHOOTING
Thenicethingaboutbuildingyourowntransceiverisbeingableto
fixitifitbreaks,ortofigureoutwhyit’snotworkingquiteright
asyouturnitonforthefirsttime,WITHOUThavingtosenditback
tousforrepair.Butwehavefoundthatmanypeoplelackbasictrou‐
bleshootingskills.Sohereareafewtipstohelpyounarrowdowna
problem:

1.StartbymeasuringthemainDCvoltagesoneveryboard.Isthe5V
supplyreally5V?Mostlogiccircuitscantoleratearangeof4.75
to5.25V.Ifit’slessthan4.75,lookintothecause—disconnect
allboardsfromtheDCDboard’spowerconnectorsandmeasurethe
voltagethere.IsitOK?Ifitis,plugtheotherboardsinoneat
atimetoseewhichoneisaffectingthevoltage.Ifnot,trouble‐
shootjusttheDCDboard.
2.Isolatetheproblemtoaboard,andthentoasectionofthat
board.Forexample,isthereceiverworkingbutnotthetransmit‐
ter?Sincethereceiverusesthesamelowpassfiltersasthe
transmitter,andtheyarelocatedonthetransmitterboard,youcan
ruleoutonewholesectionofthetransmitterboard(allthelow
passfiltertoroidsandassociatedrelays).
3.Figureoutwhatitcan’tbe,tohelpyouunderstandwhatitcanbe.
Forexample,ifplugginginthetransmittermakesthereceiverquit
working,itcouldbethatthetransmitterisloadingdownthe
shared8‐bitdatabus.Orperhapsitisdrawingtoomuchpowerand
causingthevoltagetodroptoolow.MeasureDCvoltagesfirst,to
makesurethatthecircuitsyoususpectarebadaregettingpower.
4.Replaceunknownsignalswithknowngoodones.
Forexample,ifthe
receiverdoesn’twork,isasignalmakingitallthewayfromthe
antennajackthroughtheantennaswitchontheDCDboardthrough
theSWRmetercircuit,throughthetuner,throughthelowpassfil‐
tersonthetransmitter,throughtheT/Rswitch,throughthe
band‐
passfiltersandpreampsontheRXBPFboardandallthewaytothe
RFinputjackonthereceiverboard?Lotsofcircuitsthere!Try
disconnectingthenormalRFinputandconnecttheantennainputor
anyothersourceofRFdirectlytothereceiverboard.BecauseSi‐
enna
hasalotofcableinterconnects,youhavegreatflexibility
inseparatingonecircuitfromanother.