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From: Arfa Daily on 23 Dec 2009 20:36 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
From: hr(bob) hofmann on 23 Dec 2009 22:02 On Dec 23, 7:36 pm, "Arfa Daily" <arfa.da...(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 Mery Christmas!
From: Mark Zacharias on 24 Dec 2009 06:33 "hr(bob) hofmann(a)att.net" <hrhofmann(a)att.net> wrote in message news:d25a4c09-78a3-4141-9a3b-eb48c2ca105b(a)b2g2000yqi.googlegroups.com... On Dec 23, 7:36 pm, "Arfa Daily" <arfa.da...(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 >Mery Christmas! Agreed. Merry Christmas to all the regulars here and it looks like we have nearly made it through another year of this. As frustrating as it can be, we wouldn't be doing it if we didn 't love it. Mark Z.
From: Adrian C on 24 Dec 2009 07:07 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
From: b on 24 Dec 2009 08:15
On 24 dic, 02:36, "Arfa Daily" <arfa.da...(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 well done! it's great when that happens. thanks also for posting up the solution here - might help someone else in future. maybe post a link to this solution from the original thread, for reference. -B |