Re: Consumer electronics "war stories"

[Mark Zacharias]

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.

[Cursitor Doom]

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?

[pf...@aol.com]

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 repair 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 consider the effects of same. But it sure is coincidentally suspicious - and also the fallacy of leaping to conclusions.

Peter Wieck
Melrose Park, PA

[jf...@my-deja.com]

On Thursday, March 3, 2016 at 7:50:40 AM UTC-8, pf...@aol.com wrote:
> 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 consider the
> effects of same. But it sure is coincidentally suspicious - and also the
> fallacy of leaping to conclusions.
>
> Peter Wieck
> Melrose Park, PA

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.

[Chuck]

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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[Chris Jones]

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.
https://www.flickr.com/photos/37778900@N06/25484493195/

[amdx]

On 3/3/2016 4:41 PM, Chuck wrote:
> On Thu, 3 Mar 2016 15:17:37 -0000 (UTC), Cursitor Doom
> <cu...@notformail.com> wrote:
>
>> 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?
>
> 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

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

Mikek

[Mark Zacharias]

> 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.
>

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

[Cursitor Doom]

On Thu, 03 Mar 2016 16:41:53 -0600, Chuck wrote:

> 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

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.

[Phil Allison]

pf...@aol.com wrote:
>
>
> 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 repair 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.
>

** 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