Hello all,

I have a TDS540A that was failing the acquisition board on it's power-on
self test. This unit had the problem where the small electrolytics were
leaking all over the board. After re-capping and cleaning the entire unit,
it now passes the self test, but CH3 is completely dead. I probably should
have done a preliminary functional check first, ah well... Anyway, probing
the input on the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is the
culprit. Unfortunately, I cannot determine what this part is - it has a
heatsink epoxied to the top of it, and I'm afraid of doing more damage by
trying to break the thing off. I know that Tek never released schematics
for this unit, but am hoping someone might know what the chip is. Thanks
for any help!

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's power-on
self test. This unit had the problem where the small electrolytics were
leaking all over the board. After re-capping and cleaning the entire unit,
it now passes the self test, but CH3 is completely dead. I probably should
have done a preliminary functional check first, ah well... Anyway, probing
the input on the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is the
culprit. Unfortunately, I cannot determine what this part is - it has a
heatsink epoxied to the top of it, and I'm afraid of doing more damage by
trying to break the thing off. I know that Tek never released schematics
for this unit, but am hoping someone might know what the chip is. Thanks
for any help!

It's extremely difficult for people to help you if you don't include a valid
email address.

--
Return address is VALID!

On Wed, 05 Mar 2008 21:07:20 GMT mike wrote in Message
id: cYDzj.15491$e_.6150@trnddc03:

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's power-on
self test. This unit had the problem where the small electrolytics were
leaking all over the board. After re-capping and cleaning the entire unit,
it now passes the self test, but CH3 is completely dead. I probably should
have done a preliminary functional check first, ah well... Anyway, probing
the input on the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is the
culprit. Unfortunately, I cannot determine what this part is - it has a
heatsink epoxied to the top of it, and I'm afraid of doing more damage by
trying to break the thing off. I know that Tek never released schematics
for this unit, but am hoping someone might know what the chip is. Thanks
for any help!

It's extremely difficult for people to help you if you don't include a valid
email address.

Hello,

Why? All I'm looking for is what the part # of a chip is. Follow-ups to
Usenet posts should be on Usenet, not email. I very rarely use a valid
email address, as I hate spam.

JW wrote:
On Wed, 05 Mar 2008 21:07:20 GMT mike wrote in Message
id: cYDzj.15491$e_.6150@trnddc03:

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's power-on
self test. This unit had the problem where the small electrolytics were
leaking all over the board. After re-capping and cleaning the entire unit,
it now passes the self test, but CH3 is completely dead. I probably should
have done a preliminary functional check first, ah well... Anyway, probing
the input on the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is the
culprit. Unfortunately, I cannot determine what this part is - it has a
heatsink epoxied to the top of it, and I'm afraid of doing more damage by
trying to break the thing off. I know that Tek never released schematics
for this unit, but am hoping someone might know what the chip is. Thanks
for any help!
It's extremely difficult for people to help you if you don't include a valid
email address.

Hello,

Why? All I'm looking for is what the part # of a chip is. Follow-ups to
Usenet posts should be on Usenet, not email. I very rarely use a valid
email address, as I hate spam.

The chip part number is 155-0378-xx.
My bad.
I thought you actually wanted help fixing the scope.

As all you need is the part number, I'll go back to sleep.
Sorry for the mistake.
I'll endeavor to abide by the usenet posting rules.
mike
--
Return address is VALID!

mike wrote in news:BZTzj.11258$C1.7871@trnddc07:

JW wrote:
On Wed, 05 Mar 2008 21:07:20 GMT mike wrote in
Message id: cYDzj.15491$e_.6150@trnddc03:

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's
power-on self test. This unit had the problem where the small
electrolytics were leaking all over the board. After re-capping and
cleaning the entire unit, it now passes the self test, but CH3 is
completely dead. I probably should have done a preliminary
functional check first, ah well... Anyway, probing the input on the
(unknown) PLCC device U1200 shows that the input of the chip is
permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is
the culprit. Unfortunately, I cannot determine what this part is -
it has a heatsink epoxied to the top of it, and I'm afraid of doing
more damage by trying to break the thing off. I know that Tek never
released schematics for this unit, but am hoping someone might know
what the chip is. Thanks for any help!
It's extremely difficult for people to help you if you don't include
a valid email address.

Hello,

Why? All I'm looking for is what the part # of a chip is. Follow-ups
to Usenet posts should be on Usenet, not email. I very rarely use a
valid email address, as I hate spam.

The chip part number is 155-0378-xx.
My bad.
I thought you actually wanted help fixing the scope.

As all you need is the part number, I'll go back to sleep.
Sorry for the mistake.
I'll endeavor to abide by the usenet posting rules.
mike

FYI,a 155-xxxx-xx is a TEK-made IC,out of production and no longer stocked
by TEK.

--
Jim Yanik
jyanik
at
kua.net

On Thu, 06 Mar 2008 15:21:05 GMT mike wrote in Message
id: BZTzj.11258$C1.7871@trnddc07:

JW wrote:
On Wed, 05 Mar 2008 21:07:20 GMT mike wrote in Message
id: cYDzj.15491$e_.6150@trnddc03:

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's power-on
self test. This unit had the problem where the small electrolytics were
leaking all over the board. After re-capping and cleaning the entire unit,
it now passes the self test, but CH3 is completely dead. I probably should
have done a preliminary functional check first, ah well... Anyway, probing
the input on the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is the
culprit. Unfortunately, I cannot determine what this part is - it has a
heatsink epoxied to the top of it, and I'm afraid of doing more damage by
trying to break the thing off. I know that Tek never released schematics
for this unit, but am hoping someone might know what the chip is. Thanks
for any help!
It's extremely difficult for people to help you if you don't include a valid
email address.

Hello,

Why? All I'm looking for is what the part # of a chip is. Follow-ups to
Usenet posts should be on Usenet, not email. I very rarely use a valid
email address, as I hate spam.

The chip part number is 155-0378-xx.
My bad.
I thought you actually wanted help fixing the scope.

Well, yeah, but I just wanted to know if it was Tek custom or an off the
shelf part. Given the number above, I guess that answers my question.
I'm 99% sure that that's the defective chip. Anyway, I'll have to look for
a donor scope to repair this one. Would you happen to know if the TDS520A
uses the same chip?

As all you need is the part number, I'll go back to sleep.
Sorry for the mistake.
I'll endeavor to abide by the usenet posting rules.

I hope I didn't come off as being rude, that certainly wasn't my intent. I
appreciate the help, Mike. Thanks!

JW wrote in
:

On Thu, 06 Mar 2008 15:21:05 GMT mike wrote in
Message id: BZTzj.11258$C1.7871@trnddc07:

JW wrote:
On Wed, 05 Mar 2008 21:07:20 GMT mike wrote in
Message id: cYDzj.15491$e_.6150@trnddc03:

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's
power-on self test. This unit had the problem where the small
electrolytics were leaking all over the board. After re-capping
and cleaning the entire unit, it now passes the self test, but CH3
is completely dead. I probably should have done a preliminary
functional check first, ah well... Anyway, probing the input on
the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input
to CH3 is. Swapping the coax output from the attenuator board from
another channel yields the same result, so I'm pretty sure that
U1200 is the culprit. Unfortunately, I cannot determine what this
part is - it has a heatsink epoxied to the top of it, and I'm
afraid of doing more damage by trying to break the thing off. I
know that Tek never released schematics for this unit, but am
hoping someone might know what the chip is. Thanks for any help!
It's extremely difficult for people to help you if you don't
include a valid email address.

Hello,

Why? All I'm looking for is what the part # of a chip is. Follow-ups
to Usenet posts should be on Usenet, not email. I very rarely use a
valid email address, as I hate spam.

The chip part number is 155-0378-xx.
My bad.
I thought you actually wanted help fixing the scope.

Well, yeah, but I just wanted to know if it was Tek custom or an off
the shelf part. Given the number above, I guess that answers my
question. I'm 99% sure that that's the defective chip. Anyway, I'll
have to look for a donor scope to repair this one. Would you happen to
know if the TDS520A uses the same chip?

I believe so,since they essentially are the same scope.
SW is a large part of the difference in them.
you might even be able to use the whole board in the TDS540.

--
Jim Yanik
jyanik
at
kua.net

JW wrote:
On Thu, 06 Mar 2008 15:21:05 GMT mike wrote in Message
id: BZTzj.11258$C1.7871@trnddc07:

JW wrote:
On Wed, 05 Mar 2008 21:07:20 GMT mike wrote in Message
id: cYDzj.15491$e_.6150@trnddc03:

JW wrote:
Hello all,

I have a TDS540A that was failing the acquisition board on it's power-on
self test. This unit had the problem where the small electrolytics were
leaking all over the board. After re-capping and cleaning the entire unit,
it now passes the self test, but CH3 is completely dead. I probably should
have done a preliminary functional check first, ah well... Anyway, probing
the input on the (unknown) PLCC device U1200 shows that the input of the
chip is permanently biased at about -1VDC no matter what the input to CH3
is. Swapping the coax output from the attenuator board from another
channel yields the same result, so I'm pretty sure that U1200 is the
culprit. Unfortunately, I cannot determine what this part is - it has a
heatsink epoxied to the top of it, and I'm afraid of doing more damage by
trying to break the thing off. I know that Tek never released schematics
for this unit, but am hoping someone might know what the chip is. Thanks
for any help!
It's extremely difficult for people to help you if you don't include a valid
email address.
Hello,

Why? All I'm looking for is what the part # of a chip is. Follow-ups to
Usenet posts should be on Usenet, not email. I very rarely use a valid
email address, as I hate spam.
The chip part number is 155-0378-xx.
My bad.
I thought you actually wanted help fixing the scope.

Well, yeah, but I just wanted to know if it was Tek custom or an off the
shelf part. Given the number above, I guess that answers my question.
I'm 99% sure that that's the defective chip. Anyway, I'll have to look for
a donor scope to repair this one. Would you happen to know if the TDS520A
uses the same chip?

yes they're the same chip.


As all you need is the part number, I'll go back to sleep.
Sorry for the mistake.
I'll endeavor to abide by the usenet posting rules.

I hope I didn't come off as being rude, that certainly wasn't my intent. I
appreciate the help, Mike. Thanks!

You come off as stubborn!!

If I understand what you posted here, that can't happen. Stated another
way, my interpretation of you experiments is that the results are
inconsistent.
Stated a third way, there are some other things you should try before
you go replacing the chip.

You've got an old board that's been compromised by corrosion.
Even if you have state-of-the-art SMT desoldering equipment, you're
gonna be fighting the corroded contacts and stressing a weakened board.
And I bet you 23-cents that changing the chip won't fix it. And I
predict you'll end up with additional problems.

And if you decide to replace the board, where do you think you're gonna
find a board that doesn't have the same problem? You aren't, outside
a working instrument...and even those will have the problem soon.
Nobody's gonna part out a working time bomb at a price
you want to pay.

My favorite repair axim, "If it ain't broke, don't fix it," has a
corollary, "If it's not broke too bad, don't fix it."
A three-channel TDS540 is a powerful instrument. A TDS540 with an
acquisition board you busted trying to fix, isn't.

All that aside, I've offered, on multiple occasions, to take this off-
group and help you fix it. You're too smart for your own good...
and STUBBORN!!! And I support your right to shoot yourself in the foot
as often as you see fit.

I'm gonna TRY to make this my last post on this topic...
but I'm weak and easily agitated.

mike


--
Return address is VALID!