35406Re: [softrock40] Re: softrock lite - troubleshooting the flipflop
- Aug 3 3:14 PMI knew I could count on you guys!
I had never thought of lifting a single pin. I'll do that. I did
recheck the chip orientation (which would be number one). It's ok.
I just lifted pin 3 of the flip-flop. the divider voltage is 2.53 v
now. Guess I would replace the chip now.
I have some of the fairchild 74AC74's coming. Dont know yet if they are
exact replacement. But looks right.
If y'all have any experience on that, let me know. I can canibalize a
74AC74 from the RXTX kit I have waiting on the shelf.
Where can I get replacement parts?
Tom - WA4FYN
See Me at the Huntsville Hamfest!
(or....dont let that stop you. ha)
> Hi Tom,
> The title threw my as I could not find SoftRock you were talikng
> about, but by process of elimination, got to the v9.0 RX!
> Try removing C19, then measure on the junction of R9 / R10.
> If you still have 5v on it, then try lifting pin 3 and pin 11 of U6 to
> eliminate the device itself pulling it up.
> I use some solder braid and then a sewing needle with the soldering
> iron to carefully lift up individual pins on a smd devices. Make sure
> that they really are clear of the solder pads, and do not use any
> force or you can easily pull of the PCB pad.
> Try measuring again on the junction or R9 / 10 and see what it is. If
> it is still 5v, then start looking for the solder splashes! If it is
> correct at 2.5v, then carefully push pin 3 then pin 11 back down and
> see if the junction changes. You might have cleared any short in the
> process. My bet is a short pin 3 to 4 or 10 to 11 :)
> Let us know how you get on,
> 73, Bob G8VOI
> --- In firstname.lastname@example.org
> <mailto:softrock40%40yahoogroups.com>, tmac <tmac@...> wrote:
> > Hi,
> > This is a sanity check with y'all before I lift the f-flop chip (U6- 74A
> > C74) off the board for testing.
> > The voltage divider (r9 & r10) is giving trouble. The voltage at r9-r10
> > is almost up to the 5-volt rail voltage. R9 top end is 5-volts. R10
> > bottom end is 0-v . I've pulled the two resistors and verified their
> > values. I've replaced the coupling (c19) capacitor that feeds the
> > r9-r10 junction. I've inspected every solder joint for bridges to other
> > components, and scraped between them with a pick.
> > The mid point of the divider should be 5 volts. However, there is that
> > si570 signal feeding thru the cap. Is a dc offset of the signal pulling
> > up the metered voltage? I really doubt it.
> > My conclusion is that the flipflop clock input is pulling the voltage up
> > somehow. So, I've ordered some fairchild chips (couldnt find Ti) to
> > replace the one I will lift for test in case the chip is the source of
> > the pullup.
> > Just thought I'd ask for the symptomatic information before I end the
> > life of a chip.
> > "It's all fun." It builds character." And still having fun.....
> > Have a great day!
> > Tom - WA4FYN
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