[sdiy] Tr-808 issue

[Kenny Balys]

It shouldn't do that, a square AC main will be a source of
noise but the transforer should be able to handle it.

Is there no way for you to get a scope? There may be more than one
issue and others are sure to come up.

With 808's you could have a bad trace on the motherboard that
comes and goes and this could make one think that there are bad
components.

If you haven't already, I would suggest going through and resoldering
every point in the trouble area and beyond and making a very close
visual inspection.

I had a Jupiter-6 that drove me completely bonkers until I found an
intermittent bad trace. It only went bad once the machine heated up.
The problem did not manifest when the machine was cool.




On 13.09.18 20:33 , el macaco wrote:
> Am I on the right track thinking a squarish 120vac could bugger the transformer?
>
>> On Sep 13, 2018, at 3:26 PM, el macaco <elmacaco at hotmail.com> wrote:
>>
>> Yes.  Thanks!! I have a true sine wave inverter now and it’s solid and even goes through line conditioners etc before the 808.  All the other gear works fine on it.
>>
>> The earlier set up was before I had a proper solar set up.
>>
>>
>>
>>> On Sep 13, 2018, at 2:42 PM, Kenny Balys <kenny at beatkamp.com> wrote:
>>>
>>>
>>> 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.
>>>>
>>