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From: Leonard Caillouet on 24 Dec 2009 08:58 "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message news:KAzYm.104267$II.69134(a)newsfe22.ams2... > Following on from my request earlier in the week for a schematic set for a > NAD cassete deck that was an urgent repair for Christmas, having not come > up with any diagrams, I decided today to fling it back up on the bench, > and have a go at the fault 'blind'. > > The basic problem was no record, no playback, no meter indications in > either mode. When playing back a known good test tape, there was input to > two pins of the Sony Dolby processor IC, but no signs of anything coming > out on any other pins. I couldn't even find the correct data sheet for > this device ... > > Based on the fact that the chip was surrounded by little pale blue > electrolytics, which I have had give trouble on many different items of > electronic equipment over the years, I set about measuring the resistance > to ground at every pin on the IC. Two pins, exactly opposite one another, > and with similar looking print traces, going off in the same direction, > both read pretty close to zero, When I followed the traces round the > board, they both arrived at 220uF 10v caps, sitting side by side. When > these were removed, both read short circuit. How odd is that ? When they > were replaced with 16v types, all record / play and metering functions > were restored. > > Just goes to show, with a bit of perseverence, and a lot of years' > experience, just occasionally, you *do* get lucky ... :-) > > Arfa > Glad to hear that you solved your problem. Merry Christmas and happy whatever to all. Arfa, and others, you might want to check out some of the tech forums where hundreds of techs share resources and tips. Two of the best are TechAssist and Tech-Data. Both have subscription fees in the $50-60 range, but there are hundreds of gigabytes of manuals between the two, thousands of tips, and hundreds of techs with access and experience on most brands. You also won't find the spam and nonsense that are so pervasive on Usenet. Only qualified techs in the repair business are allowed. Leonard
From: Arfa Daily on 24 Dec 2009 09:39 "Adrian C" <email(a)here.invalid> wrote in message news:7ph3rgFvdbU1(a)mid.individual.net... > Arfa Daily wrote: >> Following on from my request earlier in the week for a schematic set for >> a NAD cassete deck that was an urgent repair for Christmas, having not >> come up with any diagrams, I decided today to fling it back up on the >> bench, and have a go at the fault 'blind'. >> >> The basic problem was no record, no playback, no meter indications in >> either mode. When playing back a known good test tape, there was input to >> two pins of the Sony Dolby processor IC, but no signs of anything coming >> out on any other pins. I couldn't even find the correct data sheet for >> this device ... >> >> Based on the fact that the chip was surrounded by little pale blue >> electrolytics, which I have had give trouble on many different items of >> electronic equipment over the years, > > These capacitors are in fact the little mischievous elves that normally > assist in the distribution of power thoughout the product, but at > Christmas particulary they sit around doing nothing after a year or so of > either being exhausted, drinking too much, or just sitting there > cross-legged and idle. > > It's the cross-legged stance that causes the short circuit. At least you > don't have the mess of the ones that drank too much, got bloated and threw > up electrolyte all over the board ... > > -- > Adrian C LOL ! Have a good 'un everyone, and catch y'all in the new year ! d;~} Arfa
From: N_Cook on 24 Dec 2009 11:30 Meat Plow <meat(a)petitmorte.net> wrote in message news:3csm2c.7nl.17.9(a)news.alt.net... > On Thu, 24 Dec 2009 01:36:41 -0000, "Arfa Daily" > <arfa.daily(a)ntlworld.com>wrote: > > >Following on from my request earlier in the week for a schematic set for a > >NAD cassete deck that was an urgent repair for Christmas, having not come up > >with any diagrams, I decided today to fling it back up on the bench, and > >have a go at the fault 'blind'. > > > >The basic problem was no record, no playback, no meter indications in either > >mode. When playing back a known good test tape, there was input to two pins > >of the Sony Dolby processor IC, but no signs of anything coming out on any > >other pins. I couldn't even find the correct data sheet for this device .... > > > >Based on the fact that the chip was surrounded by little pale blue > >electrolytics, which I have had give trouble on many different items of > >electronic equipment over the years, I set about measuring the resistance to > >ground at every pin on the IC. Two pins, exactly opposite one another, and > >with similar looking print traces, going off in the same direction, both > >read pretty close to zero, When I followed the traces round the board, they > >both arrived at 220uF 10v caps, sitting side by side. When these were > >removed, both read short circuit. How odd is that ? When they were replaced > >with 16v types, all record / play and metering functions were restored. > > > >Just goes to show, with a bit of perseverence, and a lot of years' > >experience, just occasionally, you *do* get lucky ... :-) > > > >Arfa > > > > Good deal. I was always thrust into a position of a so called > emergency repair without a Sams manual or the luxury of the internet > (which Al Gore hadn't invented yet) back in the 70's-80's. > > However, the real tough dogs being intermittent faults can stifle even > the most persistent, experienced tech. Like this Singer-Kearfott > resolver driver/processor I'm working on. Nothing on the net to give > me service errata and an intermittent error displayed on the op > terminal as a PG error relates to the resolver, Funny thing is you can > get the error anywhere from immediately to several days down the road. > And the error can shut things down immediately several times in a row > then work for a week. > > As much experience as I have it doesn't substitute for a diagram > showing operation values for voltages, wave forms and digital pulses. Just going by the general appearance/style/era of that cnc board, I would suspect a via somewhere, from dealing with similar in the past, re-solder both sides of all vias -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/
From: N_Cook on 25 Dec 2009 11:17 Meat Plow <meat(a)petitmorte.net> wrote in message news:3cva81.7cr.17.3(a)news.alt.net... > On Thu, 24 Dec 2009 16:30:33 -0000, "N_Cook" <diverse(a)tcp.co.uk>wrote: > > >Meat Plow <meat(a)petitmorte.net> wrote in message > >news:3csm2c.7nl.17.9(a)news.alt.net... > >> On Thu, 24 Dec 2009 01:36:41 -0000, "Arfa Daily" > >> <arfa.daily(a)ntlworld.com>wrote: > >> > > I have enough generic info and understanding now to take it to the > second level, dynamic tests. I have the specs on the resolvers and > what they need as far as an input from the resolver amp. But I must > confess I'm not the sharpest knife in the drawer when it comes to old > TTL and A/D - D/A stuff being more of an audio and RF tech in the > days. There are no LSI devices in this thing besides the 8086 CPUs on > the logic and servo CPU boards. Also some embedded software on > EEPROMS. Not being formally trained on TTL has hampered my > troubleshooting but I am finally starting to 'get it'. It's hard to > adapt to a primitive TTL aggregation that was replaced with LSI less > than a decade later. I was just getting into digital control, PLL, > etc.. when LSI started being used more and more making it much easier > to verify the operation of the circuit by data I/O on the pins of an > LSI rather than to understand the mathematics of data flow between > dozens of seperate TTL devices. If one clock only then a trick I used once for tracing a digital fault in similar circumstances. I managed to change the clock crystal to 100KHz or maybe was a glass cased 10KHz one, can't remember, long ago. Clock worked and slowed everything down so much that it highlighted, by little happening, on a suspect ,actually dead TTL device. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/
From: Michael A. Terrell on 25 Dec 2009 11:23
Leonard Caillouet wrote: > > Merry Christmas and happy whatever to all. Merry Christmas, you old buzzard! ;-) Merry Christmas to everyone. :) -- Offworld checks no longer accepted! |