Consumer electronics "war stories"

Um.... Um....

Have you checked the receptacle at home? And for proper polarity?

Some monitors will not function if not properly polarized. Just a thought.

Peter Wieck Melrose Park, PA

Reply to
pfjw
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Who when where how why what?

I don't think that's the problem of I would have been electrocuted long ago. However, it was worth checking, especially since I did my own wiring. So I dug out my tester: and walked it through the maze of power strips and extension cords. Everything tests just fine.

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Reply to
Jeff Liebermann

Okay, one more. True story... This wasn't so much a difficult repair as it was the circumstance. 1980, hot summer day and my new girlfriend (who wou ld be my wife) is having her HS graduation party when her parent's early 70 s tube Magnavox console blacks out in a cloud of smoke leaving a clean hori z line. I was 21 at the time and looked younger, but of course being a TV tech I was asked to look at it. I pulled the chassis out and the area arou nd the vert centering control was pitch black. That and the cigarette smok e and wood stove deposits made seeing what else was burned nearly impossibl e.

I borrowed the garden hose and a bottle of Fantastik (TM) and soaked the bo ttom of the chassis and rinsed so it sparkled, then left it out front in th e hot sun. Later in the afternoon I put in two 10 ohm 5W resistors in place of the vert cent control and put it together, touched up the height and li n and it worked fine for a few more years.

When my father in law tells the story, he said that when he saw me hosing o ut the TV guts in the front yard he was thinking "oh sh$t I'm going to have to buy a new TV tomorrow".

Reply to
John-Del

Same thing happened to my younger brother when our family was visiting the family of the older brother's wife.

Zenith TV died. My younger brother, who was either still in tech school or early in his career, tore the set down to bits and pieces right there on the living room floor, puzzled over it a bit, the light came on, ran down to the Zenith distributor, picked up a part, got back over there and finished the repair.

Two families (not to mention the two brothers) were sweating bullets on that one.

Mark Z.

Reply to
Mark Zacharias

John-Del wrote: "When my father in law tells the story, he said that when he saw me hosing out the TV guts in the front yard he was thinking "oh sh$t I'm going to have to buy a new TV tomorrow".

Good story with happy ending! Nowadays most folks won't let me adjust their PICTURE menus for them, let alone go component level. Sets are so reliable today, with consistent image quality, yet people wonder why they burn out after only 3-5 years.

Backlit TVs(LCD, LED) require a backlight to be seen, and very often this setting, along with the others, are left in factory/showroom mode, shortening the life of the appliance. Getting set owners to understand this basic fact, along with the benefits of correct setting of the basic adjustments(brightness, contrast, color, etc), is well-nigh impossible! A $300 full calibration is often not necessary to achieve these goals.

Reply to
thekmanrocks

Sometimes you have to set aside a "dog" and get on to other stuff.

Sanyo JA-V14:

Late 80's rack-type integrated amp, electronic switching and volume. Uses flat cables to the other components. Uncommon model - not much info on them out there.

Standard blown channel. Replaced the outputs and a number of drivers, resistors, etc.

Let us just say that access for service was really bad. I deal with units all the time with no bottom access but even given that, this was much worse than usual.

Had to work on it opened up clamshell style at a 90 degree angle working in between the main board and bottom chassis.

It also didn't help that there was a shrink-wrapped .1uF at 500V bodged in underneath and glued to the board right over the pre-drivers I needed to replace.

It was original brown gooey stuff - not yellow glue turned bad. So anyway, I get the parts replaced but the bias won't adjust right, the voltage across the emitter resistors was all over the place. Occasionally the relay would come on but mostly there was a 70 volt offset.

Had to purchase the PDF service manual online. The manual was poor quality and the schematic drawn in a fairly unusual way, of course.

I beat my head into this thing but wasn't really getting any further. Eventually I had to set it aside for more pressing business, including that Yamaha M-80.

This was in late November and December.

A couple days ago, business was slow and I reluctantly got back into this thing. I could only run it maybe 30 seconds at a time to take voltage readings across

this emitter-base junction, across this resistor, etc. Changed out the differential pair and the current source transistors - no good.

Finally decided I didn't think there was anything preventing the early stages from working correctly - the transistors replaced, resistors checked OK.

Transistors forward biased. The circuit should be balanced but was not.

Now, normally there should be about 2.2 volts across the bias transistor E-C. There was, but overall it was 70 volts above ground. Something was leaking from the positive rail to the bias transistor.

You may have guessed by now. It was the glue. Just a tiny portion of it bridged across two adjacent foil runs - not corrosive but appears like ash. Measured 80 ohms from the bias transistor to the positive rail, in the megohm range on the other channel.

Cleaned the area and cleared the "accidental resistor". Problem resolved.

Resoldered the IC voltage regulators and put it back together.

I can't retire soon enough.

Mark Z.

Reply to
Mark Zacharias

On Thu, 03 Mar 2016 06:08:18 -0600, Mark Zacharias wrote: [...]

I saw something about this on someone's YT channel a few days ago with respect to the old late 70s CB radios where the goo becomes conductive over time and shorts parts of the PCB out. The bloke who was explaining it was convinced the manufacturers did it on purpose. I'm not convinced myself, but who knows for sure?

Reply to
Cursitor Doom

This comes under the same sort of scrutiny as the foam speaker surrounds of the early 80s into the 90s, you know the ones that rotted about 45 seconds after the warranty expired and created an entirely new industry in the rep air of these speakers.

How could so many manufacturers make the same mistake all at the same time? And most of them were the old-line Boston Sound makers - Advent, AR, EPI, KLH and more who should really have known better. My guess is that none of them considered the omnipresence of ozone around today, and so did not cons ider the effects of same. But it sure is coincidentally suspicious - and al so the fallacy of leaping to conclusions.

Peter Wieck Melrose Park, PA

Reply to
pfjw

The surrounds on my AR-2ax's from about 1967 are still good. They are made of rubberized cloth (probably silicone rubber). The acoustic suspension concept requires having a good seal, and foam would not work.

Reply to
jfeng

It was rumored that the glue was made by Sony and that they sold it to other manufacturers but didn't use it themselves until many years later. T

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Reply to
Chuck

I think it might be used much more recently too. I have a DVB-T set top box that used to work fine but started locking up and generally crashing. The PCB had some brown glue that got dabbed in various places including around a RAM chip and onto some 0402 components. THe glue had started to discolour and it looked like it was corriding the components. I picked off the glue and cleaned it a bit with solvent and I think I replaced one decoupling capacitor and now it works fine, no crashing.

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Reply to
Chris Jones

I don't know who made amn sold it, but Sony products also had the glue (resistor) problem.

Mikek

Reply to
amdx

The Advents were acoustic suspension. When the surround was good the piston motion of the woofer was damped , apparently enough to do the job.

mz

Reply to
Mark Zacharias

Sony, yes it was them; I remember now. The goo was suspicious as it was commonly used on high impedance areas of the boards of multiple manufacturers where there was no ostensible need for it.

Reply to
Cursitor Doom

** You can add Bose and JBL to that list.

First time I saw crumbling surrounds was on a pair of JBL LE8Ts sold in 1970 - lasted less than 5 years. The local ( Australian) JBL agents replaced the cones at no cost when the owner complained bitterly about it.

Interestingly, the use of foam surrounds was taken up by nearly all makers in the USA but few elsewhere. In the Europe and the UK, rubber roll surrounds were the norm: eg KEF, Celestion, Philips, Seas and Wharfedale woofers.

Neoprene rubber has a indefinite life and many such woofers from the 70s are still working today.

.... Phil

Reply to
Phil Allison

Circa 1987

Harman Kardon HK-400XM:

Three-head cassette deck.

Intermittent failure to record on one channel. Playback fine.

Customer sent to HK twice for factory service.

Twice HK replaced the record / play head assembly. Problem persisted.

On the bench, at failure mode, discovered full peak-to-peak bias at the output of the affected channel, swamping out the audio.

Defective (intermittent coil) in bias trap. IIRC a small module.

That customer still looks me up 30 years later when he has a problem.

Couple years later, same problem on a Kenwood KX-1030. Open coil.

Over 30 years - never seen this since.

Mark Z.

Reply to
Mark Zacharias

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