Received a nonworking GPX C971 Cassette/CD Boombox for repair learning experience.

Used DVM to check Ohms on AC and DC connections Both were infinity for power switch off and on.

Am guessing the problem is a blown fuse.

Checked the forum using keywords "GPX C971" got nothing.

Googled using keywords "GPX C971 schematic" also nothing.

Am sure that the the schematic is on the Internet so would be interested in help finding it.

Thanks

Ken

On Mon, 22 Dec 2014, KenO wrote:

Received a nonworking GPX C971 Cassette/CD Boombox for repair learning
experience.

Used DVM to check Ohms on AC and DC connections Both were infinity for
power switch off and on.

Am guessing the problem is a blown fuse.

Checked the forum using keywords "GPX C971" got nothing.

Googled using keywords "GPX C971 schematic" also nothing.

Am sure that the the schematic is on the Internet so would be interested
in help finding it.

But what isn't working?

I've had boomboxes that wouldn't work without batteries. They were needed
to run the clock and remember the memories. I assumed they'd not be
needed when plugged into the wall, but that wasn't the case. Sometimes
they have a set of aa cells in there for that purpose, besides D cells
that aren't needed if powered off AC.

I recall the radio didn't work without the batteries, I can't remember
what else happened. But the radio is the easiest thing to check, and that
may be the problem. I recall not seeing anything on the LCD display until
I did put in batteries, but it's been a while.

Michael

"Michael Black" wrote in message
xample.org...
On Mon, 22 Dec 2014, KenO wrote:

Received a nonworking GPX C971 Cassette/CD Boombox for repair learning
experience.

Used DVM to check Ohms on AC and DC connections Both were infinity for
power switch off and on.

Am guessing the problem is a blown fuse.

Checked the forum using keywords "GPX C971" got nothing.

Googled using keywords "GPX C971 schematic" also nothing.

Am sure that the the schematic is on the Internet so would be interested
in help finding it.

But what isn't working?

I've had boomboxes that wouldn't work without batteries. They were needed
to run the clock and remember the memories. I assumed they'd not be
needed when plugged into the wall, but that wasn't the case. Sometimes
they have a set of aa cells in there for that purpose, besides D cells
that aren't needed if powered off AC.

I recall the radio didn't work without the batteries, I can't remember
what else happened. But the radio is the easiest thing to check, and that
may be the problem. I recall not seeing anything on the LCD display until
I did put in batteries, but it's been a while.

Michael



All valid observations, but any kind of older boombox will likely have a
straightforward linear supply utilising a power transformer. The primary of
such is almost invariably connected straight across the power socket, and so
can be read on a meter set to ohms. The OP said that he had a reading of
infinity across the AC ...

Whilst there might be a separate fuse, this is often not the case,
protection being afforded by a thermal fuse buried in the primary. The on /
off switch is also never in the primary circuit. This is always either a
mechanical switch in the main low voltage supply rail, or a tactile switch
read by the system control micro, which then outputs a control signal to
turn on sleeping parts of the power supply.

If the unit uses a 'figure 8' AC socket, this is the first place to look. It
is extremely common for these to go bad jointed, often on just about every
pin. This can give the symptoms described, because not only is it the AC
input socket, it also has a switch that 'rolls over' when the plug is
inserted. This switch controls where the DC to run the set comes from i.e.
either from the secondary side of the AC power supply, or from the
batteries.

Arfa

Arfa Daily wrote:


Whilst there might be a separate fuse, this is often not the case,
protection being afforded by a thermal fuse buried in the primary. The on /
off switch is also never in the primary circuit.


** OK - what exactly does a buried thermal fuse "protect" - I mean the one shot variety as found in small to medium size transformers ?

Cannot be the transformer, since fuse operation it renders it unusable.

It does not limit the max current flow like a wire fuse, cos operation depends on a critical temp being reached.

The answer is, it protects the user from possible electric shock by preventing overheating damage to the transformer.

A thermal fuse disconnects the primary from the supply *before* the enamel insulation or the plastic bobbin become dangerously hot.



..... Phil

KenO wrote:

Checked the forum using keywords "GPX C971" got nothing.

Googled using keywords "GPX C971 schematic" also nothing.

No surprise there.

GPX was probably an importer who bought stuff cranked out of chinese or
korean factories and slapped their name on it.

It was real low end **** that mostly ended up in drug stores, flea markets
and "wholesale distributors to the public".

If there was any service or repair on those, it probably was limited to
bringing it back to where you bought it and crossed fingers they exchanged
it or gave a refund.

You'll have to hunt and peck to make an attempt to repair it, but not sure
what you'll learn from the experience except how low quality can something
be made but if you put it in a fancy enough case, someone will buy it.

-bruce

Thanks everyone for your comments.

Guess I need to elaborate so will try.

Michael Black: I was unable to see anything turn on with either batteries or AC when pushed the power button On and Off a number of times.

What tests do you suggest I run?

Arfa Daily: "If the unit uses a 'figure 8' AC socket, this is the first place to look...." Again what tests do you suggest I run? Can I post a JPEG of the AC socket?

Bruce Esquibel: "not sure what you'll learn from the experience..." At this time do not know. If nothing else will use it for parts. Was surprised that it does not look like it was abused so am tending to agree "It was real low end ****..."

Am still surprised I can not find a service manual or basic schematic for GPX C971?

These have to be somewhere out there? Maybe under another Name?

Any ideas how to identify the Chinese Mfr?

Open to all suggestions.

Ken

KenO wrote:
Thanks everyone for your comments.

Guess I need to elaborate so will try.

Michael Black: I was unable to see anything turn on with either batteries or AC when pushed the power button On and Off a number of times.

What tests do you suggest I run?

Arfa Daily: "If the unit uses a 'figure 8' AC socket, this is the first place to look...." Again what tests do you suggest I run? Can I post a JPEG of the AC socket?

Bruce Esquibel: "not sure what you'll learn from the experience..." At this time do not know. If nothing else will use it for parts. Was surprised that it does not look like it was abused so am tending to agree "It was real low end ****..."

Am still surprised I can not find a service manual or basic schematic for GPX C971?

Highly unlikely there was ever a service manual for something like that.

These have to be somewhere out there? Maybe under another Name?

nope.

Any ideas how to identify the Chinese Mfr?

It probably came out of a grade school.

Open to all suggestions.

You don't really need a schematic to fix a boombox, and if there was one,
it would probably be wrong anyways.

Here's a checklist to start with- without even trying to be a jerk:

Does it power on?
Is it plugged in?
Is the cord good?
Is there power making it to the power supply?
Does the power supply work?
If not, what's broken?
replace bad part, try again
-Or- fire t up with bench power supply. If other stuff is broken, just
toss it unless it's of sentimental value.

"Phil Allison" wrote in message
...
Arfa Daily wrote:


Whilst there might be a separate fuse, this is often not the case,
protection being afforded by a thermal fuse buried in the primary. The on
/
off switch is also never in the primary circuit.


** OK - what exactly does a buried thermal fuse "protect" - I mean the one
shot variety as found in small to medium size transformers ?

Cannot be the transformer, since fuse operation it renders it unusable.

It does not limit the max current flow like a wire fuse, cos operation
depends on a critical temp being reached.

The answer is, it protects the user from possible electric shock by
preventing overheating damage to the transformer.

Well it certainly protects the transformer and rest of the unit from
catching fire, which is probably all the manufacturer is interested in.
Whilst a separate 'true' fuse in the primary might save the transformer from
damage in the event of a short or lesser overload on the secondary side,
manufacturers aren't going to be the slightest bit interested in the cost
versus advantage of this, when they can buy a transformer that is already
intrinsically safe by virtue of having a thermal fuse in its primary.

Arfa

A thermal fuse disconnects the primary from the supply *before* the enamel
insulation or the plastic bobbin become dangerously hot.



.... Phil

"KenO" wrote in message
...
Thanks everyone for your comments.

Guess I need to elaborate so will try.

Michael Black: I was unable to see anything turn on with either batteries
or AC when pushed the power button On and Off a number of times.

What tests do you suggest I run?

Arfa Daily: "If the unit uses a 'figure 8' AC socket, this is the first
place to look...." Again what tests do you suggest I run? Can I post a
JPEG of the AC socket?

I thought I was fairly clear, Ken. "The first place to look" means exactly
that. I then went on to say "It is extremely common for these to go bad
jointed, often on just about every
pin." So, if it uses a 'figure 8' power lead - obvious, because it looks
like a figure "8" end on - then open up the unit until you can see where the
socket is soldered into a printed circuit board, then engage your mk 1
eyeball and look at the joints on the socket pins to see if any of them are
cracked around. If you don't understand what I am meaning or what that would
look like, then I think that you are probably ****ing in the wind believing
that you will be able to correctly diagnose and repair it. Sorry if that
sounds harsh, but welcome to the reality of repairing electronic items like
this ...

Arfa

Ken