[sdiy] Tr-808 issue

Maarten diy at artefacts.nl
Fri Sep 14 08:50:26 CEST 2018


I have seen this problem several times, sometimes the 808 will not start 
up or random resets occurs during playing a pattern. It was caused by a 
flaky transistor in the power on/off muting circuit. I replaced 1 of the 
transistors, I can not recall which one. So I would advice you to 
replace all 3 transistors in the power on/off muting circuit, Q10, Q11 
and Q12.

Cheers,
Maarten

Op 13-9-2018 om 23:42 schreef el macaco:
> It powers on with no step Leds lit, just bank a and section 1 leds Lot with no change with toggles switched.
> 
> It’s the power protection circuit.  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.
> 
> Maybe a faulty trace on the clock circuit looks just like the protection circuit kicking in?
> 
> Thanks guys.  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 :/.
> 
> Giving me new fire to crack this problem.
> 
>> On Sep 13, 2018, at 3:51 PM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>>
>> If it's a cheap inverter that outputs a "squarusoidal" waveform, then it's more likely to make the transformer buzz loudly or to damage the smoothing capacitors and rectifier diodes.
>>
>> Is your unit definitely configured for 120VAC, and not 240VAC?  Supplying the unit with the wrong voltage will obviously result in no operation or possible damage (if over-voltage.)
>>
>> Is the TR-808 completely dead?  or does the sequencer (CPU) still function, LEDs flash, etc?  It sounds more like a problem with the CPU's power-on reset, or possibly the audio output muting?
>>
>> -Richie,
>>
>> -----Original Message----- From: el macaco
>> Sent: Thursday, September 13, 2018 9:33 PM
>> To: Kenny Balys
>> Cc: synth-diy at synth-diy.org
>> Subject: Re: [sdiy] Tr-808 issue
>>
>> 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.
>>>>>
>>>
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