Tektronix 2445 Readout is no good , video included

[[email protected]]

http://video.yahoo.com/video/play?vid=1466538

The readout looks bad , i can see jumpy dots ,instead of clear numbers
as in the other 2445 .
i replaced those 3 47uf caps on the A5 board (control board) , and it
didn't helped .
http://img110.imageshack.us/img110/2372/image015pn5.jpg

 

[Jim Yanik]

http://video.yahoo.com/video/play?vid=1466538

The readout looks bad , i can see jumpy dots ,instead of clear numbers
as in the other 2445 .
i replaced those 3 47uf caps on the A5 board (control board) , and it
didn't helped .
http://img110.imageshack.us/img110/2372/image015pn5.jpg

2445 non-B scopes have separate R-O boards.
the signal from them feeds into the vertical on the main bottom board.
try swapping the readout boards.
IIRC,there's also a pot to adjust R-O crawl/jitter.
see the cal procedure in your service manual.

On "B" models,the readout is integrated to the A5 uP board.
"B" model A5 uP boards are NOT swappable with earlier versions.

 

[JW]

http://video.yahoo.com/video/play?vid=1466538

The readout looks bad , i can see jumpy dots ,instead of clear numbers
as in the other 2445 .
i replaced those 3 47uf caps on the A5 board (control board) , and it
didn't helped .
http://img110.imageshack.us/img110/2372/image015pn5.jpg

I'll second what Jim has said with regards to the jitter pot. On very
early serial numbers, the pot and a few passive components were tack
soldered to U800 (An ECN I guess - I just replaced a U800 on a 2465 that
had this). On later serial numbers, R805 was added to the A1 board. It
couldn't hurt to give it a twiddle.

 

[[email protected]]

2445 non-B scopes have separate R-O boards.
the signal from them feeds into the vertical on the main bottom board.
try swapping the readout boards.
IIRC,there's also a pot to adjust R-O crawl/jitter.
see the cal procedure in your service manual.

On "B" models,the readout is integrated to the A5 uP board.
"B" model A5 uP boards are NOT swappable with earlier versions.

--
Jim Yanik
jyanik
at
kua.net

tried play with jitter , didn't do the trick ...

and you are right about A5 in the 2445 , the R-O is not on this
board , i just did a swap with a good 2445 A5 and got the same jerky
readout .

what component is making the problem in the R-O of the 2445 ?
caps ? or something else ?

 

[Jim Yanik]

tried play with jitter , didn't do the trick ...

and you are right about A5 in the 2445 , the R-O is not on this
board , i just did a swap with a good 2445 A5 and got the same jerky
readout .

what component is making the problem in the R-O of the 2445 ?
caps ? or something else ?

possibly caps,or a bad hybrid on the main board.
Does it twitch in the vert or horiz direction,or both? signal trace
solid,in both V and H axes?
This may be where you have to scope every decoupled PS supply line.
could even be some of those 0.1uf DIP caps that are all over every board.

 

[[email protected]]

[email protected]:








possibly caps,or a bad hybrid on the main board.
Does it twitch in the vert or horiz direction,or both? signal trace
solid,in both V and H axes?
This may be where you have to scope every decoupled PS supply line.
could even be some of those 0.1uf DIP caps that are all over every board.

--
Jim Yanik
jyanik
at
kua.net

trace is solid , no trace problems .

and one thing i noticed , when i control the read out intensity fully
CW , the R-O shifts upwards ...

 

[Jim Yanik]

trace is solid , no trace problems .

Is that a trace with a signal displayed,or just the baseline trace?
With a signal displayed,you can see any horiz jitter.
Without an input signal,you can't see any jitter in the horiz.

and one thing i noticed , when i control the read out intensity fully
CW , the R-O shifts upwards ...

I wonder if your CRT is maxed out on intensity.(grid bias)

 

[[email protected]]

Is that a trace with a signal displayed,or just the baseline trace?
With a signal displayed,you can see any horiz jitter.
Without an input signal,you can't see any jitter in the horiz.




I wonder if your CRT is maxed out on intensity.(grid bias)

--
Jim Yanik
jyanik
at
kua.net

i'l try with a signal later on ...

and i adjusted the grid bias , its fine .

 

[[email protected]]

Is that a trace with a signal displayed,or just the baseline trace?
With a signal displayed,you can see any horiz jitter.
Without an input signal,you can't see any jitter in the horiz.




I wonder if your CRT is maxed out on intensity.(grid bias)

--
Jim Yanik
jyanik
at
kua.net

Well , the read-out is good now , i replaced the power supply , and
don't have jerky read-out .
i guess power supply ain't that good .

but i got another problem with this scope , the horiz is not good at
some of time bases , some of them ok , but lets say 5u is drifting .
i did CAL 01-04 , but got LIMIT warning in the horiz section , could
not adjust as required .
something is wrong , what i'm doing wrong ?

 

[Jim Yanik]

Well , the read-out is good now , i replaced the power supply , and
don't have jerky read-out .
i guess power supply ain't that good .

probably marginal electrolytics,bad ESR.
often,the PS is the source of trouble appearing elsewhere.

but i got another problem with this scope , the horiz is not good at
some of time bases , some of them ok , but lets say 5u is drifting .
i did CAL 01-04 , but got LIMIT warning in the horiz section , could
not adjust as required .
something is wrong , what i'm doing wrong ?

All the parts for timing are on the sweep hybrids.try swapping the A and B
sweep hybrids,and recal.if the problem goes away on that range/mode,then yu
have a bad hybrid.

 

[[email protected]]

probably marginal electrolytics,bad ESR.
often,the PS is the source of trouble appearing elsewhere.




All the parts for timing are on the sweep hybrids.try swapping the A and B
sweep hybrids,and recal.if the problem goes away on that range/mode,then yu
have a bad hybrid.

--
Jim Yanik
jyanik
at
kua.net

Well , gonna try this after i'l find new U800 (Horiz amp ) just
destroyed the one that was on the scope .

the horiz amp got nothing to do with the timing ?

do you know where i can find U800 ?

 

[Jim Yanik]

Well , gonna try this after i'l find new U800 (Horiz amp ) just
destroyed the one that was on the scope .

the horiz amp got nothing to do with the timing ?

do you know where i can find U800 ?

they aren't made anymore,and the only place you can get one is from another
2445/65 scope.IIRC,there was an Ebay seller who had some salvaged ones for
sale,but the price was pretty high.

 

[[email protected]]

they aren't made anymore,and the only place you can get one is from another
2445/65 scope.IIRC,there was an Ebay seller who had some salvaged ones for
sale,but the price was pretty high.

--
Jim Yanik
jyanik
at
kua.net

i'l try to salvage ...

the horiz amp got nothing to do with the timing ?

 

[Jim Yanik]

i'l try to salvage ...

the horiz amp got nothing to do with the timing ?

why don't you read the excellent circuit description that's in the service
manual?

 

[[email protected]]

why don't you read the excellent circuit description that's in the service
manual?

--
Jim Yanik
jyanik
at
kua.net

Well all good now , replaced U800 , replaced hybrids , timing is
good .

great , thanks .