sci.electronics.repair@googlegroups.com

Google Groups

Cursitor Doom <curd@notformail.com>: Sep 22 10:46AM Gentlemen,   When inspecting a board for the likely cause of an intermittent fault believed to be induced by warming up over time from switch-on, what/which is/are the most likely suspects to be considered blameworthy? I'm guessing dry joints has to be on the list somewhere, but what components can also give rise to this issue?       -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

Stephen Wolstenholme <steve@easynn.com>: Sep 22 12:34PM +0100 On Sun, 22 Sep 2019 10:46:57 -0000 (UTC), Cursitor Doom >is/are the most likely suspects to be considered blameworthy? I'm >guessing dry joints has to be on the list somewhere, but what components >can also give rise to this issue?   Any component can have thermal problems. I would check the ones that feel hot after a few minutes.   Steve   -- http://www.npsnn.com

Cursitor Doom <curd@notformail.com>: Sep 22 11:48AM On Sun, 22 Sep 2019 12:34:22 +0100, Stephen Wolstenholme wrote:   > Any component can have thermal problems. I would check the ones that > feel hot after a few minutes.   Normally I would go around with a can of freezy spray and dob various parts of the board looking for the fault to go away, but sadly in this case it's not possible as the board in question is one of these slot-in types that are inaccessible to investigation when the instrument is under power. :(           -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

Phil Allison <pallison49@gmail.com>: Sep 22 04:53AM -0700 Cursitor Doom wrote: --------------------   > When inspecting a board for the likely cause of an intermittent fault > believed to be induced by warming up over time from switch-on,   ** If the problem appears after a time delay an warming - it ain't a fucking intermittent.   FYI:   I was presented with a Yamaha digital reverb some years ago ( model R1000) that worked fine until it got a bit hot. Then it broke into a very loud, harsh noise - bit like pink noise.   The only thing I could find that triggered the noise was heating the micro-controller with my soldering iron - so I ordered a new one ( not cheap) and fitted it. Made no fucking difference.   So I rang the Australian agent and described the problem to one of their staff service people - with an Asian accent (his not mine) - he went off and checked the files for relevant service bulletins.   Came back with one entitled "Big Noise".   " If the unit emits a loud noise when operating in a high ambient temp replace ICs 1,2 3, 4 ,5 ,6 ... "   The problem was a damn design fault in the first 10,000 sold !!!   The fix was to replace all the regular CMOS data selectors with high speed ( HC ) ones. Once carried out, the problem vanished.   Seems the CMOS logic used had a timing issue, exacerbated by high temps.   More BS than this little Koala can bear ...     .... Phil

tabbypurr@gmail.com: Sep 22 05:57AM -0700 On Sunday, 22 September 2019 11:46:59 UTC+1, Cursitor Doom wrote: > is/are the most likely suspects to be considered blameworthy? I'm > guessing dry joints has to be on the list somewhere, but what components > can also give rise to this issue?   Anything.     NT

Mike Coon <gravity@mjcoon.plus.com>: Sep 22 03:02PM +0100 In article <qm7n2t$m6n$4@dont-email.me>, curd@notformail.com says... > case it's not possible as the board in question is one of these slot-in > types that are inaccessible to investigation when the instrument is under > power. :(   Decades ago there was always a standard extension board that plugged into the motherboard in place of the questionable one and carried only a socket that the one under investigation could be plugged into to make it accessible, so long as the covers were off...   Mike.

Cursitor Doom <curd@notformail.com>: Sep 22 04:39PM On Sun, 22 Sep 2019 15:02:22 +0100, Mike Coon wrote:   > into the motherboard in place of the questionable one and carried only a > socket that the one under investigation could be plugged into to make it > accessible, so long as the covers were off...   Yes, and the service engineers would no doubt have been issued with them. The service engineers would also no doubt have been issued with duplicate sets of identical boards to swap-out, thereby saving heaps of their very expensive time on each job. This particular instrument is a 10Mhz-22Ghz spectrum analyser (one of two I have made by Hewlett-Packard) so those engineers sent out into the field to fix them would have been very well-supported by HP. Unfortunately, however, I'm not one of them! However, the fault appears to be somewhere in the x-amplifier board and they used *exact* same board for the y-amplifier so at least I can compare them. There's no point now in swapping them over as I now *know* the fault lies somewhere in the x- amp one.       -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

Jeff Urban <jurb6006@gmail.com>: Sep 21 07:58PM -0700 On Friday, September 13, 2019 at 12:05:10 PM UTC-5, jf...my-deja.com wrote: > All of these anecdotes remind me of the complaints about TV repair men charging $50 to replace a 25-cent capacitor if you brought it in to the shop, and $100 if he came out to your place. The argument always was that part of the charge was for knowing which part to replace.   It is. It cost us many hours to learn which part to replace and we could not lay that all on the first customer. How would YOU like to be that customer. Have any idea what that time costs ? It wasn't just my ton of money an hours it was lights, heat or A/C. Internet, phone, cable TV. We needed it. As a customer you pay a piece of that, no matter what business.   The places I worked had the best BBB rating there is. We were the ones to go testify against other shops of goniffs. We were the ones who fixed shit these dickhead couldn't, and they came in their house, took out a board and left and then called and said it would be like $600 to fix. And then we fixed it for half that and had the customer go get the board from that guy - AND FOUND IT WAS NOT THE PROBLEM !   So, I will change the cap(s) in your condenser unit for fifty bucks plus the caps, plus transportation. I'll put those bitches out of business as well, and not lose a minute sleep over their starving kids.   These days when I do a job some want to pay me more than I ask. I got a 40% tip on an amp repair.   If you are near Cuyahoga county it might be worth me doing something but I doubt it. But then you don't need it, I think...

Adam <adamg@pobox.comNOSPAM>: Sep 21 10:03PM > PFC correction & the ability to run at 120 & 240 without changing a > switch are of course 2 separate things.   The typical PFC circuit is a boost regulator placed between the rectifier and the reservoir cap. In this way, the reservoir cap can charge during the entire AC cycle instead of only during the peaks, improving the power factor. But this also has the effect that the PWM circuit will see the same input voltage regardless of the line voltage. So, wide input range often comes along with PFC.   -- Adam

Phil Allison <pallison49@gmail.com>: Sep 21 06:19PM -0700 Adam wrote: -----------   > and the reservoir cap. In this way, the reservoir cap can charge during > the entire AC cycle instead of only during the peaks, improving the power > factor.   -------------------------------------------------------------   ** Most PFC circuits have damn near sine wave current draw, so the PF is around 0.9 to 0.95. However, with the vast majority of domestic, electronic appliances this is of no advantage to the user or the supply system. Only lighting and computers are required to have good PFs in places like Europe and the US while the main reason for that is cos it allows twice as many of these to run from the same AC supply, compared to non PFC versions.   Many buildings have hundreds of light fittings installed and large numbers of mains powered PCs for workers - and that is where it matters!   FYI: domestic fridges, microwave ovens plus most washers and clothes driers have long had near sine wave current draw and so good power factors.   > But this also has the effect that the PWM circuit will see the > same input voltage regardless of the line voltage. So, wide input range > often comes along with PFC.   ** Correct.     ..... Phil

Jeff Urban <jurb6006@gmail.com>: Sep 21 07:36PM -0700 >** Yeah - the cct starts off in the 240V position and jumps >down to the 120V setting if the output voltage is much too low.   That's what I thought but being in a 120 volt country never had to deal with it.   >It's safer to have the setting locked to the AC voltage where >you live - and not have it jump to voltage doubling cos of a >short term voltage drop.   That makes perfect sense in a 240 country.   Here, it can't really hurt itself.   There are some high power amps here that need 240. They just can't run on 120. Those don't switch down.   Anyway yes, you are definitely better off with a switch.

Klay Anderson <mailserver.cctv@gmail.com>: Sep 21 10:07AM -0700 And support for Windows Me, XP, and Mac OS6 is over. Moore's Law. Time......marches on.

You received this digest because you're subscribed to updates for this group. You can change your settings on the group membership page. To unsubscribe from this group and stop receiving emails from it send an email to sci.electronics.repair+unsubscribe@googlegroups.com.