[sdiy] Tr-808 issue

el macaco elmacaco at hotmail.com
Fri Sep 14 23:37:49 CEST 2018


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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