old HP1740A o'scope problem

Bill Martin

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Sep 30, 2015, 12:25:00 AM9/30/15

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Hi,
Anyone have a list of "usual suspects" with this HP1740A scope when
there is no display at all? Front panel lights seem working, but that is
all I find so far. Have not opened the case yet, nothing seems to "smell
bad" so far. I won't be stressed if it can't be fixed, I bought it for
the nice rolling stand it was sitting on...I have another similar,
slightly newer antique scope that is still working that can use that stand.

TIA,
Bill M

JC

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Sep 30, 2015, 8:19:42 AM9/30/15

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All the interboard connections on these are suspect for dry/bad joints
especially on the power board where you can get a nice burn up from the
arcing. Also the vertical output chip fails so you will get a trace but
no deflection. If you can go over all the joints carefully you might
have an easy repair.

Bill Martin

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Sep 30, 2015, 6:26:35 PM9/30/15

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Nice to know. Thanks for the info.

Bill Martin

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Oct 1, 2015, 3:49:17 PM10/1/15

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On 09/30/2015 05:19 AM, JC wrote:

Ok, I opened it up, there do not seem to be any burn marks on anything.
Wiggled the connectors too. Should I be able to see a glow from the ctr
filament without removing the metal shielding? So far I see no light,
nor detect any warming near the neck end of the tube...one additional
data point: the red "reset" led on the front panel is on all the time,
and there is no illumination of the faceplate.

Tom Miller

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Oct 1, 2015, 4:35:42 PM10/1/15

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"Bill Martin" <w...@wwmartin.net> wrote in message
news:muk2k0$1q6$1...@dont-email.me...

Do you have a copy of the service manual? Have you checked the power supply
test points? Be careful, there are some points that can bite you.

The screen illumination is done by a flood gun.

Do you have another scope?

Regards,
Tom

Bill Martin

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Oct 1, 2015, 5:05:32 PM10/1/15

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I do have another scope...it is even working. No service manual for this
one, I have the 1743A service manual, which should be "close" at least.
Yeah, I know about being bitten, got 300Vdc from a Klystron plate cap
once. Long ago, but you don't forget. So far all I have done is
superficial, really obvious kind of stuff. Not likely to put a lot of
effort into this, since fixing it could easily cost more than it is
worth...just curious what is ailing. I'm suspicious of the crt itself at
this point. If I can get it working, will likely give it away, to
another "old guy" buddy that could use it.

Bill

Tom Miller

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Oct 1, 2015, 7:52:04 PM10/1/15

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"Bill Martin" <w...@wwmartin.net> wrote in message

news:muk730$kb4$1...@dont-email.me...

Pretty good copy here:
http://www.ko4bb.com/manuals/index.php?dir=HP_Agilent/HP_1740_Oscilloscope

It really is not a bad scope. Good to over 100 MHz, two channel w/ delayed
sweep.

It could be something minor like a bad capacitor in the power supply. Go
check the supplies first.

Also, you will need to figure out how to fab some new feet as the originals
are most likely gone.

Good luck and 73

Bill Martin

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Oct 2, 2015, 2:15:09 PM10/2/15

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Thanks for that, and yes, the feet on both my scopes are falling apart.

Bill