Maker Pro
Maker Pro

SONY STR-DE635 NO POWER UP

M

Matt

Jan 1, 1970
0
Greetings:

I have a Sony STR-DE635 5.1 amp.

The other day I woke up to find that the only thing that happens on
power up is the sound made by some small realy clicking somewhere.

I checked all the fuses, and all are OK.

As there is no display, power light, etc - I'm _guessing_ a power
supply problem.

If it helps any, I generally (used to) leave it on 24 x 7.

I've obtained the schematics, and will begin a bit more detailed work
soon.

However, I thought I would ask here first for any other likely areas to
check first.

ME: By no means a qualified electronics tech, however I understand
power supply theory, purposes and functions of the standard electronic
compoinent family, can use a volt/ohm/ammmeter; and am quite good at
soldering/desoldering, and can also read a schematic with no problem.

What I don't have is a workbench with the standard tools needed to
carry out a reapir like this, although I do have a digital VOM and a
variety of various wattage soldering irons.

In other words I'm clueless.

I've since replaced the amp, but I could use this one to power my
outdoor sound system if I can get it working again.

Any comments are most appreciated.

Matt
 
Check main transformer primary and secondary.

Relay click indicates the standby transformer and system control is
probably ok.

Are you sure you do not get an overload message on display and then
shutdown? If yes, then main power supply has a problem.

If you did not have enough ventilation, it is very possible that the
thermal protect cutoff inside the transformer on the primary has gone
open (pretty common). Transformer is very expensive to replace.

Getting a hold of the smaller thermal protect fuses that go inside the
transformers will be difficult at best as no one seems to carry them in
single quantities.

If anyone has a supplier for those 4A thermal cutoffs used inside the
transformers please post.
 
M

Matt

Jan 1, 1970
0
THANK YOU

Yes, no overload message present - all power display functionality is
dead (for example, muting/bass button light are dead, nothing appears
on LED display at any time).

This will be a junker amp; can you give any tips as to how to get
inside the transformer to check the fuse? I cant see any way to get in
it.

Thanks again

Matt
 
Typically you will see three wire connections on the primary, two going
to the ac line, one all by itself. The two that look like a thick
solid wire are usually the thermal fuse. You may have to remove the
plastic guard to get at it.

Simply measure the primary of the transformer to see if it is open
before going any further to see if there is a thermal fuse open.

No, you won't see it, it is embedded inside the wrapping inside the
transformer. Sometimes it can be carefully removed and replaced, but
rarely.
 
M

Matt

Jan 1, 1970
0
Yep, primary wide open.

Operation destroy transformer (in all likeliehood) underway. Oh well.
Not as oif I can really make it any worse.

Anyone got any good supply house reccs for transformers?

Thanks
Matt
 
Can you post some decent digital pictures of the transformer somewhere?
I can then repost the picture with a marking showing where the thermal
cutoff is hiding and how to get at it, if it is possible on yours.
 
M

Matt

Jan 1, 1970
0
I don't have a camera here, Ill see if my sis will let me borrow hers.

BUT - wouldn't do any good anyway, as ALTHOUGH THE TRANSFORMER IS NOW
WORKING (Notice, I Didn't say "REPAIRED") - and all system functions
appear normal...... I still have NO IDEA where the thermal fuse is.

I'll describe my approach as best as possible:

I followed the primary leads in to the transformer. In this case,
Orange and white.

Covering the top of the primary windings was a plastic layer; cant
really describe it but it sort of looked like a row of widely spaced
teeth.

Ripped all that out off both top and bottom. A screwdriver and some
needlenose pliers, and then the plastic was gone.

Now, where the primary feed leads go into the transformer, I noticed
what I believe you called "the third lead" tucked down in front of the
primary windings.

Using a small screwdriver, I "untucked it, and it appeared to somply be
2 wires soldered together. As I recall, it had zero resistance to the
white primary lead.

Now I flipped the transformer over and just started digging in the same
space that the above wires went into. I had no idea what I was looking
for, what it looked like, where it was, or how I could possibly get to
it even if I knew any of the above.

In the end, the screwdriver I was using easily passed _through_ the gap
between the primary and secondary windings, and the orange and white
leads had long since been ripped from wherever they were connected to.

All that was left were 2 leads. 1 on the 'inside' of the primary
winding, on the bottom of the transformer, and 1 on the 'outside' of
the primary winding, on the top of the transformer. My hope was that
these were simply the beginning and ending of the primary winding.

So, to answer your question about the thermal fuse.... I don't think it
exists anymore. There is a large pile of what looks like very fine sand
on my work table though.

I got a measurement of 1.5 ohms across the leads, and figured that
should make a nice big spark or a blackened outlet when I plugged it
in. But hey, I know NOTHING of what primary windings should ohm out at,
and so long as it wasn't at ZERO, I was willing to give it a shot.

Placed everything on top of a box (its in a few zillion pieces), and
plugged the 3 or 4 seconday connectors in. Plugged the front panel in,
gritted my teeth, stood back as far from the outlet as I could and
still get the plug in, and .... ZOWIE, all the indicators lit up,
relays clicked, LEDs sparkled to life, and apparantly other then a
transformer thats a 'bit' more dangerous now then it was before, I
apparantly have a working amp again.

So I guess my answer is pry around in there with a small screwdriver,
you'll dig some paper out, eventually you will find the beginning and
end of the primary, and there ya go.

Personally I'm quite pissed that the fuse was there in the first place.
I can see the need for monitoring an overheating transsformer. I can
also see an easy way to do it wothout burying a fuse inside of it. Is
this part of the built in obsolescence program?

Other then maybe unplugging it when not in use, anyone have any
suggestions on how to return a bit of safety to the xformer?

Ill still try to take some pics to give ya an idea of all hte hackery I
talked about tonight.

Finally, when looking for info on this problem, I ran across a source
that said another cause of this problem is shorted or failing output
power transistors. Bear with me guys, I don't know the proper term, but
the big huge honking transistors mounted to the massive heat sinks.

Looking at their solder connections, it does indeed they have spent
quite a warm life.

What do ya say, should I go ahead and replace them as well? And if so,
anything else?

Thanks much,
Matt
 
The thermal fuse is there due to safety regulations to prevent a fire.
An overheating transformer is one of the easiest ways a device like
that can start a fire.
 
M

Matt

Jan 1, 1970
0
Well sure, I agree - but certainly, a design could be made where it is
also replaceable.
 
R

Rono

Jan 1, 1970
0
J

jango2

Jan 1, 1970
0
A blown thermal fuse might mean a compromised enamel coating on the
winding. Hence the regulating authorities would rather have us replace
the entire transformer.
Psst , just between u n me, i've bypassed a couple of thermal fuses and
billed the customers. Guilty as sin !
Jango
 
Top