- Harman Kardon Citation 17 Pre-Amp One Channel Intermittent - 4 Updates
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- Tektronix 565 repair - 1 Update
| John-Del <ohger1s@gmail.com>: Mar 22 11:31AM -0700 On Thursday, March 22, 2018 at 12:25:55 AM UTC-4, Ron D. wrote: > I'd measure the DC at the speaker terminals before and during a fault first. > I'd expect something initially and probably zero if your loosing contact. > Then do the same, but before the relay. He won't be picking up any dc on the outputs. The other channel remains. If it was a DC fault detect, the relay would open and both sides would go out. Besides, the DC detect is hair trigger on these and the meter probably wouldn't resolve the value before the relay opened. A min/max peak recorder feature on the dmm might catch it but even that isn't guaranteed. The easiest thing to do if the relay is suspected is to thwack it while the channel is out (but not hard enough to bounce to effect a contact bounce). If the contacts are gimpy, something will be heard on the mute channel. The problem could be anywhere. If he has pre amp in/out jumpers on the back panel, he could remove them and put in short RCA cables and cross them to see if the drop out moves to the other side. If so, it's before the junction, if not, it's after. The easiest thing to do is trace it with a scope when the channel acts up. The problem is that once you get near an intermittent circuit with a scope probe, the problem clears up.. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Mar 22 12:05PM -0700 This weekend will be the testing. A new relay (exact fit) is $80 from the same company that made them for HK. Not bad for an obsolete part. but about 10X the cost of a similar unit. But the gentleman at Computer Components stated that their manufacturing specs called for "matched reeds". The relay is also large enough to open and have a look. Peter Wieck Melrose Park, PA |
| jurb6006@gmail.com: Mar 23 07:43AM -0700 Check the tape monitor(s) first. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Mar 23 07:54AM -0700 > Check the tape monitor(s) first. I will. Peter Wieck Melrose Park, PA |
| "Gareth Magennis" <soundserviceleeds@outlook.com>: Mar 22 08:36AM wrote in message news:0d0ae1ec-e3dc-4ddf-b84e-0226fa2609a1@googlegroups.com... I hate those things. (figure of speech) Exactly what happens to the speaker output when it fails ? ************************************* This: http://tinypic.com/view.php?pic=316x93t&s=9#.WrNoppcuDIU Total sweep time across the screen here is 2.4 seconds. I can only describe it as sounding like "boing, boing boing", with a boing every 0.8 seconds. It is not VERY loud at all, nothing that would damage the speaker as far as I can tell, but this screenshot is the unfiltered output of the amps, not the filtered waveform the speaker sees. There are a whole bunch of inductor/cap/resistors between the amps and speaker. Gareth. |
| "Gareth Magennis" <soundserviceleeds@outlook.com>: Mar 22 09:27AM "N_Cook" wrote in message news:p8vrrh$r8t$2@dont-email.me... On 21/03/2018 22:17, Gareth Magennis wrote: Are both amps, audio speaking , in phase or deliberately out of phase live Yamaha Stagepas (reduces the sag on reservoir caps on peak demand) ****************************************** They both share the same PSU rails, not like Stagepass. The PWM signal to one amp input is inverted, making this standard bridge mode. PSU is an SMPS. Gareth. |
| gregz <zekor@comcast.net>: Mar 22 08:02PM > vdc on power supply diagram. Not sure where that came from. > Thanks > Gregj 500 was changed to 300 vdc in my schematic. Greg |
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