Is it just me or...
in [Repair]
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From: JW on 14 Jul 2010 06:16 So there you are, working on something that you don't have any schematics for; (in this case a Datron 1281 8.5 digit DMM) This one wouldn't power up. Poking around I noticed some (TTL) circuits were not getting +5VDC. Traced it back through a three terminal linear regulator to it's AC input. Hmmm... Only getting about 5.5VAC, not enough there. Isolate the AC output from the transformer to make sure it wasn't a loading issue; it's not. Gets to about 5.8VAC. This unit has two toroid transformers, and the one I've traced the problem to has 8 wires on the secondary and another 8 on the primary (sheesh) I have no idea what the primary voltages should be (As it turns out, about 16VAC. Weird!) BUT, suddenly I hear a metallic sounding "tick!" and the unit begins running. (I quickly measure the primaries and note the voltages JIC.) sounds a bit like a relay, but there's nothing like that in any of the power supplies (there's a number of them) that I can see. Figuring an intermittent somewhere I begin jiggling connectors, tapping around with a screwdriver handle, etc. Nothing. Meter keeps working. Cold blasts from freeze spray, Heat gun, etc. Nothing. Turn it off for an hour and back on repeating what I did above. Still working. Turn it off for a day and back on. Wash, rinse, repeat. still working perfectly. Things like this seem to happen to me often. Is it just me, or do you have faults like this that drive you nuts? I don't suppose anyone might have any schematics for this meter, would they? I think at some point Datron sold off to Wavetek then Fluke ended up with it, as the user manual is available from Fluke. Thanks.
From: Jamie on 14 Jul 2010 11:32 JW wrote: > So there you are, working on something that you don't have any schematics > for; (in this case a Datron 1281 8.5 digit DMM) This one wouldn't power > up. Poking around I noticed some (TTL) circuits were not getting +5VDC. > Traced it back through a three terminal linear regulator to it's AC input. > Hmmm... Only getting about 5.5VAC, not enough there. Isolate the AC output > from the transformer to make sure it wasn't a loading issue; it's not. > Gets to about 5.8VAC. This unit has two toroid transformers, and the one > I've traced the problem to has 8 wires on the secondary and another 8 on > the primary (sheesh) > > I have no idea what the primary voltages should be (As it turns out, about > 16VAC. Weird!) > > BUT, suddenly I hear a metallic sounding "tick!" and the unit begins > running. (I quickly measure the primaries and note the voltages JIC.) > sounds a bit like a relay, but there's nothing like that in any of the > power supplies (there's a number of them) that I can see. Figuring an > intermittent somewhere I begin jiggling connectors, tapping around with a > screwdriver handle, etc. Nothing. Meter keeps working. > > Cold blasts from freeze spray, Heat gun, etc. Nothing. > > Turn it off for an hour and back on repeating what I did above. Still > working. > > Turn it off for a day and back on. Wash, rinse, repeat. still working > perfectly. > > Things like this seem to happen to me often. Is it just me, or do you have > faults like this that drive you nuts? > > I don't suppose anyone might have any schematics for this meter, would > they? I think at some point Datron sold off to Wavetek then Fluke ended up > with it, as the user manual is available from Fluke. > > Thanks. > > Electrolytics will intermit like this. Change all that are in the power supply section.
From: stratus46 on 14 Jul 2010 11:45 On Jul 14, 8:32 am, Jamie <jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote: > JW wrote: > > So there you are, working on something that you don't have any schematics > > for; (in this case a Datron 1281 8.5 digit DMM) This one wouldn't power > > up. Poking around I noticed some (TTL) circuits were not getting +5VDC. > > Traced it back through a three terminal linear regulator to it's AC input. > > Hmmm... Only getting about 5.5VAC, not enough there. Isolate the AC output > > from the transformer to make sure it wasn't a loading issue; it's not. > > Gets to about 5.8VAC. This unit has two toroid transformers, and the one > > I've traced the problem to has 8 wires on the secondary and another 8 on > > the primary (sheesh) > > > I have no idea what the primary voltages should be (As it turns out, about > > 16VAC. Weird!) > > > BUT, suddenly I hear a metallic sounding "tick!" and the unit begins > > running. (I quickly measure the primaries and note the voltages JIC.) > > sounds a bit like a relay, but there's nothing like that in any of the > > power supplies (there's a number of them) that I can see. Figuring an > > intermittent somewhere I begin jiggling connectors, tapping around with a > > screwdriver handle, etc. Nothing. Meter keeps working. > > > Cold blasts from freeze spray, Heat gun, etc. Nothing. > > > Turn it off for an hour and back on repeating what I did above. Still > > working. > > > Turn it off for a day and back on. Wash, rinse, repeat. still working > > perfectly. > > > Things like this seem to happen to me often. Is it just me, or do you have > > faults like this that drive you nuts? > > > I don't suppose anyone might have any schematics for this meter, would > > they? I think at some point Datron sold off to Wavetek then Fluke ended up > > with it, as the user manual is available from Fluke. > > > Thanks. > > Electrolytics will intermit like this. Change all that are in the power > supply section. But 'lytics do not explain the 5.8 VAC with no load. G²
From: Cydrome Leader on 14 Jul 2010 12:18 In sci.electronics.repair JW <none(a)dev.null> wrote: > So there you are, working on something that you don't have any schematics > for; (in this case a Datron 1281 8.5 digit DMM) This one wouldn't power > up. Poking around I noticed some (TTL) circuits were not getting +5VDC. > Traced it back through a three terminal linear regulator to it's AC input. > Hmmm... Only getting about 5.5VAC, not enough there. Isolate the AC output > from the transformer to make sure it wasn't a loading issue; it's not. > Gets to about 5.8VAC. This unit has two toroid transformers, and the one > I've traced the problem to has 8 wires on the secondary and another 8 on > the primary (sheesh) > > I have no idea what the primary voltages should be (As it turns out, about > 16VAC. Weird!) Does this unit use an IEC type power receptable with some sort of voltage changing/fuse module that might need to be reseated or checked?
From: Jamie on 14 Jul 2010 13:17
stratus46(a)yahoo.com wrote: > On Jul 14, 8:32 am, Jamie > <jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote: > >>JW wrote: >> >>>So there you are, working on something that you don't have any schematics >>>for; (in this case a Datron 1281 8.5 digit DMM) This one wouldn't power >>>up. Poking around I noticed some (TTL) circuits were not getting +5VDC. >>>Traced it back through a three terminal linear regulator to it's AC input. >>>Hmmm... Only getting about 5.5VAC, not enough there. Isolate the AC output >>>from the transformer to make sure it wasn't a loading issue; it's not. >>>Gets to about 5.8VAC. This unit has two toroid transformers, and the one >>>I've traced the problem to has 8 wires on the secondary and another 8 on >>>the primary (sheesh) >> >>>I have no idea what the primary voltages should be (As it turns out, about >>>16VAC. Weird!) >> >>>BUT, suddenly I hear a metallic sounding "tick!" and the unit begins >>>running. (I quickly measure the primaries and note the voltages JIC.) >>>sounds a bit like a relay, but there's nothing like that in any of the >>>power supplies (there's a number of them) that I can see. Figuring an >>>intermittent somewhere I begin jiggling connectors, tapping around with a >>>screwdriver handle, etc. Nothing. Meter keeps working. >> >>>Cold blasts from freeze spray, Heat gun, etc. Nothing. >> >>>Turn it off for an hour and back on repeating what I did above. Still >>>working. >> >>>Turn it off for a day and back on. Wash, rinse, repeat. still working >>>perfectly. >> >>>Things like this seem to happen to me often. Is it just me, or do you have >>>faults like this that drive you nuts? >> >>>I don't suppose anyone might have any schematics for this meter, would >>>they? I think at some point Datron sold off to Wavetek then Fluke ended up >>>with it, as the user manual is available from Fluke. >> >>>Thanks. >> >>Electrolytics will intermit like this. Change all that are in the power >>supply section. > > > > But 'lytics do not explain the 5.8 VAC with no load. > > G� lets see.. ~ DC = 5.8*sqrt(2) = 5.8*1.414 = 8.2; So, with the head room required for a 5 V reg 78xx styles.. 8.2-2 = 6.2 on the average.. I put in more than the normal head room requires just to be safe on the cal's. This gives you at least 1 volt to play with... This is all fine if you have good working caps on the device that is giving you the DC inside, mainly the rectifier.. So, putting all that in context, I'd still be checking for the caps in the power supply! Test the DC voltage on the input of the REG>>>> Jamie. |