I have a SONY model KV27TS30 27" TV set that has a problem with
color. My last enquiry to this group said it is the degausser unit.
Fantastic diagnosis for I am able to locate a cold solder joint on one
of the relay pins right away.

This is a 1990 model and works just great all these years. Its the
second cold solder joint that developed, the first one being a cable
connector pin on the PCB that affected the scan lines. Seems to be a
SONY thing to have solder joint fail eventually.

Okay. The relay has three soldered on pins on a one sided PCB.
Silkscreened lines on the component (non conductor) side showed where
the relay pins go to the other components.

All conductor traces are on the opposite side (anyway at least around
the areas that I am working on.) The weird thing is there doesn't
seem to be any conducter traces from two of the pins to connect to
something else. In particular the pin with the cold solder joint
seems to be on an isloated donut pad. This pad disappeared when I
put a hot iron to it leaving a bare scar on the PCB. The other two
pins had good solder joints. I desoldered them to see if the first
pin had the conductor trace on the hidden side. There isn't.

I can always solder on a jumper wire where the silkscreen traces
indicate a connection from the pin to the other connection. Before I
do that is there any explanation to what I just described about a
relay that appears to have only one conductor trace?

"PaPaPeng" wrote in message
...
| I have a SONY model KV27TS30 27" TV set that has a problem with
.....

| Before I
| do that is there any explanation to what I just described about a
| relay that appears to have only one conductor trace?

Some PCBs have more than two layers. Can you shine a strong light through
the board?

N

On Wed, 27 Oct 2004 18:19:44 GMT, "NSM" wrote:


"PaPaPeng" wrote in message
.. .
| I have a SONY model KV27TS30 27" TV set that has a problem with
....

| Before I
| do that is there any explanation to what I just described about a
| relay that appears to have only one conductor trace?

Some PCBs have more than two layers. Can you shine a strong light through
the board?

N


Nope. Its 1990 technology though by then there was already large scale
integration that reduced the TV main cct to a single PCB. Still DIP
dimensions though. There was no need for multi layer boards.

PaPaPeng,

First, let me mention that I'm no expert on TV sets in general, and I
don't know your model at all.

Often on something like a relay there are pins that are not used, since
often there are normally open and normally closed contacts, and only one
of them is used. The unused contact often gets a isolated solder pad
just to mechanically mount the relay, as they are relatively heavy.

Regards,
Tim Schwartz
Bristol Electronics


PaPaPeng wrote:

I have a SONY model KV27TS30 27" TV set that has a problem with
color. My last enquiry to this group said it is the degausser unit.
Fantastic diagnosis for I am able to locate a cold solder joint on one
of the relay pins right away.

This is a 1990 model and works just great all these years. Its the
second cold solder joint that developed, the first one being a cable
connector pin on the PCB that affected the scan lines. Seems to be a
SONY thing to have solder joint fail eventually.

Okay. The relay has three soldered on pins on a one sided PCB.
Silkscreened lines on the component (non conductor) side showed where
the relay pins go to the other components.

All conductor traces are on the opposite side (anyway at least around
the areas that I am working on.) The weird thing is there doesn't
seem to be any conducter traces from two of the pins to connect to
something else. In particular the pin with the cold solder joint
seems to be on an isloated donut pad. This pad disappeared when I
put a hot iron to it leaving a bare scar on the PCB. The other two
pins had good solder joints. I desoldered them to see if the first
pin had the conductor trace on the hidden side. There isn't.

I can always solder on a jumper wire where the silkscreen traces
indicate a connection from the pin to the other connection. Before I
do that is there any explanation to what I just described about a
relay that appears to have only one conductor trace?

On Thu, 28 Oct 2004 13:12:16 GMT, Tim Schwartz
wrote:

PaPaPeng,

First, let me mention that I'm no expert on TV sets in general, and I
don't know your model at all.

Often on something like a relay there are pins that are not used, since
often there are normally open and normally closed contacts, and only one
of them is used. The unused contact often gets a isolated solder pad
just to mechanically mount the relay, as they are relatively heavy.

Regards,
Tim Schwartz
Bristol Electronics


Thanks for the responses. The jumper wire fixed the problem.

On the traces, while the donut left a bare patch of PCB that didn't
seem to have any connection to a conductor in fact there is a wide
ground plane like conductor patch. It is sealed under a thick
conformal plastic coat such that unless I looked closely, there didn't
appear to be anything under that coat.

There are only three pins on the relay. If it functioned on only two
pins I figured there is no way a relay would work that way.