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Old 1st Aug 2011, 7:54 pm   #11
Top Cap
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Join Date: Mar 2006
Location: Watford, Hertfordshire, UK.
Posts: 1,270
Default Re: circuit diagrams.

Graham, the way I do it is this. Draw a rough outline of the board and components, I guess you could use a digital camera now, shows when I did the last pcb
Then annotate each component i.e. R1 R2 C1 etc then identify each wire end as being either N S E or W i.e. North, South etc.
Compile a list which might go something like
R1-N
R1-S
R2-E
R2-W
continue until you have all nodes tabled then write alongside each where they go e.g.
R1-N C1-N TR1c
R1-S + supply
R2-E R3-N TR1e
R2-W 0V
When the list is complete you would have actually checked each node more than once,e.g. Checking TR1e should have R2-E and R3-N against it.
The process is a bit long winded, good for winter nights though in front of the telly but the end result enables you to draw a circuit diagram. I actually place the components down in the same orientation so R2 would be horizontal with its right hand leg (East) going to R3-N and TR1e. Hope this description gives you some idea how I do it but be prepared to redraw the circuit a few times as you find the circuit layout opens out, if you know what I mean. When I have arrived at the best draw I then sit down in front of the PC and do a 'proper' one to save or print.
With regards to using a circuit diagram for repair, yes I always endeavour to obtain one if I can. Knowing the fault, the circuit allows me to analyse and come up with the best test sequence. My best ever was looking at a Philips G8 that had intermittent Green. I viewed the circuits and arrived at the conclusion that it could be a Tantalum perhaps? on the RGB board. I changed what I considered to be the most likely culprit and presto! Green now perfect, a fault found just by analysing the circuit diagram. Priceless!
Les
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