[sdiy] Tr-808 issue

Nathan Trites nathan at idmclassics.net
Sat Sep 15 05:08:55 CEST 2018

I want to hear what's wrong with the oscilloscope now, too :)


On Fri, Sep 14, 2018 at 5:37 PM, el macaco <elmacaco at hotmail.com> wrote:

> So after months of not working I switch it on to test and the motherfucker
> works fine.  Sheesh.  Even still, I expect it to fail the same way as soon
> as I put the screws in.
> The only transistor in the protection circuit I didn’t replace was the 733
> I couldn’t get locally.  Will get some to have it all new.
> Also will check sync switch wiring although I did continuity test them and
> they were fine.
> Tony, that sounds possible, the wires to the power switch I’ve had to
> reattach a few times and I’ve heard that the cable position can wipe some
> memory locations on power up.
> Will check for .6v across those resistors when it fails again.
> I will get my scope situation sorted ASAP since I do miss it dearly.
> Don’t really want to hike with it for 4 hours to get it serviced in town,
> which should be possible.  The 808 no one can handle here,  just too
> rustic, but they repair everything here so they have scopes and rewind
> transformers etc.
> Thanks everyone for all the guidance! I will switch it on everyday to
> catch it slipping and keep diagnosing or replacing every damned part in the
> thing.  I have time....
> Would like to know tho.  Thanks for clearing the transformer of suspicion,
> which was what I would have done had I not asked.
> Gratefully,
> El
> On Sep 14, 2018, at 3:06 PM, Richie Burnett <rburnett at richieburnett.co.uk>
> wrote
> >> ...Sometimes switching it on and leaving it on for a while it will come
> to life with the step led blinking sudddenly.
> > One time I got it to live by plugging a Pedal into the start stop jack.
> Sometimes with the din sync switch but only once or twice.
> >> ...It’s been months of sometimes, then I thought I fixed it, it worked
> reliably for weeks, then when I put all the screws back in it didn’t work.
> >
> > Definitely sounds like a loose connection somewhere or a cracked PCB
> track to me.  If it was due to the UVLO/brown-out circuitry it would either
> work or not work at a particular supply voltage, not work intermittently.
> >
> > As others have said, I think you're either gonna need an oscilloscope,
> or to hand it over to someone who's got one to find out which signals have
> gone absent when it is in the non-working state.
> >
> > -Richie,
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