[sdiy] Tr-808 issue

[Kenny Balys]

Are you certain of the AC power coming in to the 808?

I would suspect that as much as the power transformer.






On 13.09.18 19:30 , el macaco wrote:
> Hello all,
>
> I’m asking for guidance to fix my Tr-808.  I usually fix my gear myself but this has me stumped.
>
> I live in the amazon far from any reliable techs and have mostly serviced my own stuff over the years with all I have learned from this list since 1999.
>
> My TR-808 has an issue where the voltage protection circuit kicks in and doesn’t let it run.  This happens when the power is unstable in the 808 and is by design.
>
> It first happened after running it from a solar power system with a voltage inverter that wasn’t pure sine wave power.
>
> The power supply was giving uneven power, 15.6v and -14v.
>
> Replacing the parts in the power supply, rectifier diodes, capacitors, regulators, resistors helped some but it doesn’t reliably work although the voltages were even 15/-15.
>
> The only power supply part I haven’t replaced is the transformer, which puts out static 26v AC voltage as required, but my oscilloscope is busted so it’s with a DMM so I can’t see if there’s ripple or other problems.
>
> That’s the next part I need to order, the transformer.
>
> Does anyone know how to test the transformer without a scope?
>
> Or is there something else that can cause this protection circuit to engage?
>
> I also replaced capacitors and transistors in the protection circuit in case that was the issue, it helped some initially but it still only works occasionally.
>
> The service manual
> Mentions something about malfunctioning IC can cause this circuit to engage.
>
> If the transformer doesn’t help next on the list is replacing the electrolytic capacitors that filter the power at each circuit (25 total I think).
>
> Any ideas greatly appreciated.
>