Teac AG-790 has me stumped...
in [Repair]
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From: Arfa Daily on 30 Jun 2010 20:44 "William R. Walsh" <wm_walsh(a)hotmail.com> wrote in message news:a5cd455f-6fdc-4b58-b994-7a7be2be5f0d(a)q12g2000yqj.googlegroups.com... > Hi! > >> Yes, as long as the relay is closing, you can measure offset at the >> speaker terminals, with one slight reservation. In the case that you can >> hear nothing at all from the speakers, but you hear the relay close, you >> need to make sure that having closed, the relay is actually staying >> closed. > > I am pretty sensitive to the noises of relays and such, and if one > does something out of the ordinary, I usually catch it in a sort of > "and what do you think you're doing?" moment. (My hearing is also good > enough to catch a lot of high frequency noises that some circuits > make, and that has clued me in to a few problems on other repairs.) > > This one really does seem to stay closed. It produces pretty > noticeable clicks and clacks. > >> What's the circuit designation of the new cap that you've found to be >> bad ? > > I am not near the receiver now and will have to look. > >> I note you say that you are using the cap checking facility on your >> multimeter. What parameter does this measure ? Capacitance >> maybe ? > > While the meter itself seems to be of decent quality and pretty > accurate, the directions that came with it are poor and do not discuss > how to do anything except voltage and resistance checks. Even those > are very poorly expressed by way of poorly written or translated > instructions. > > The display reading in the "cap test" mode is expressed in nano or > microfarads, although the test seems to be limited to low voltage and > capacitance levels. So it would appear to be useless outside of small, > low voltage capacitors. > > For those that seem to exceed the ceiling on the meter, I've done a > simple resistance test on the caps. A neighbor suggested this method, > and stated that a good cap would slowly charge up and that the > resistance reading would gradually increase while it did so. This > seems to be true. Every "bad" cap that I've found using this method > has either been open circuit or shown a high resistance reading that > did not change much/at all from the initial reading. > > At some point I do want to invest in a proper ESR meter, and the Bob > Parker meter is the one I planned to get. If and when finances > allow... > > Every suspicious cap has been removed from the circuit for testing. > This most recent one had a heat-shrunken plastic jacket. > > William Heat distress like that is always a good reason to reach for the ESR meter .... Seriously though, as soon as you can afford it, invest in one. The "Blue" is very reasonably priced, and is a fine performer. You'll never regret a day of owning it. The thing that makes an ESR meter different from the static DC tests that you are carrying out at the moment, is that it applies high frequency AC to the cap, which is what is required to arrive at a true ESR value. It is this use of low voltage AC, which also makes the meter able to perform its test with the component still in-circuit, which is a huge advantage, particularly when a board is hard to get out of equipment. This assumes of course, that you can get to the cap's leadouts on the top side of the board. Arfa
From: Cydrome Leader on 2 Jul 2010 14:58
William R. Walsh <wm_walsh(a)hotmail.com> wrote: > Hi! > >> So what does the cap do in the circuit ? Is it a big secret, or >> something ? > > No, should it be? :-) > > I don't know for certain what it does. I haven't explored it that > closely. I only noticed it being bloated out of the corner of my eye, > so I said "that should be replaced". > > I've put it aside for now. Maybe another day. > > TEAC has been no help. Although they did respond to my request asking > for more information, they recommended "shotgunning" the unit. (Yeah, > really.) a good description of shotgunning: http://www.troubleshooters.com/tpromag/200510/200510.htm#_Appropriate_Shotgunning |