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2013-10-28 by cxacxu
2013-10-28 by Lorne Hammond
Did you recap the power supply? One the 909 it is possible to overheat a thin trace hidden under one of teh big caps. Also I put in new transitors and acps and one of them was actually bad. I raelly suspect your power supply. Lorne
From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of cxacxu Sent: October-27-13 9:08 PM To: vintagesynthrepair@yahoogroups.com Subject: [vintagesynthrepair] Strange TR-808 reset problem Got a strange problem with an 808 here, the CPU will only start up when the +15v rail is disconnected. When +15v is connected the CPU does not start and the first light of step 1 does not light, the 5V and +/-15V rails are all steady, When the +15V is disconnected the cpu will start up and the sequencer will run. Any thoughts? L
2013-10-28 by kslinkard@...
First thing I would look at is how clean and accurate the power supply voltages are.
----- Original Message ----- From: "cxacxu" <cxacxu@...> To: vintagesynthrepair@yahoogroups.com Sent: Sunday, October 27, 2013 10:07:39 PM Subject: [vintagesynthrepair] Strange TR-808 reset problem Got a strange problem with an 808 here, the CPU will only start up when the +15v rail is disconnected. When +15v is connected the CPU does not start and the first light of step 1 does not light, the 5V and +/-15V rails are all steady, When the +15V is disconnected the cpu will start up and the sequencer will run. Any thoughts? L
2013-10-28 by cxacxu
First thing I would look at is how clean and accurate the power supply voltages are.
From: "cxacxu" <cxacxu@...>
To: vintagesynthrepair@yahoogroups.com
Sent: Sunday, October 27, 2013 10:07:39 PM
Subject: [vintagesynthrepair] Strange TR-808 reset problem
Got a strange problem with an 808 here, the CPU will only start up when the +15v rail is disconnected. When +15v is connected the CPU does not start and the first light of step 1 does not light, the 5V and +/-15V rails are all steady, When the +15V is disconnected the cpu will start up and the sequencer will run. Any thoughts?L
2013-10-28 by Lorne Hammond
II still distrust the power supply, so retest it at multiple points and walk your way down it towards the CPU and look for shorted connections, something going to ground etc. Also test from the other end at the power inputs for the cpu and work back from there. Look for the caps to ground as well. Is it possible to reverse the -15 and +15 connections? Its been a while since I opened mine. Lorne
From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Lorne Hammond Sent: October-27-13 11:09 PM To: vintagesynthrepair@yahoogroups.com Subject: RE: [vintagesynthrepair] Strange TR-808 reset problem Did you recap the power supply? One the 909 it is possible to overheat a thin trace hidden under one of teh big caps. Also I put in new transitors and acps and one of them was actually bad. I raelly suspect your power supply. Lorne From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of cxacxu Sent: October-27-13 9:08 PM To: vintagesynthrepair@yahoogroups.com Subject: [vintagesynthrepair] Strange TR-808 reset problem Got a strange problem with an 808 here, the CPU will only start up when the +15v rail is disconnected. When +15v is connected the CPU does not start and the first light of step 1 does not light, the 5V and +/-15V rails are all steady, When the +15V is disconnected the cpu will start up and the sequencer will run. Any thoughts? L