Thanks Victor, the heat sink is actually electrically isolated. It also has just enough clearance that you would really have to do some damage to the scope in order to get it to impact. Good piece of advice none the less.
Jeff
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On 1/20/2013 3:45 PM, victor_j_silva wrote:
Doubtful it's heat related. The chip runs at ~117F with no heatsink, that's pretty low.
Search for U800 you'll find hundreds if not a thousand posts on the subject.
Be careful with how large a heatsink you attach to the studs. A little bang on the bottom of the scope and you'll short out the -5V supply.
--Victor
--- In TekScopes@... <mailto:TekScopes%40yahoogroups.com>, Jeff Machesky wrote:
Is all of this heat related? One of the first things I did when getting
my 2465BDM was strap a very large heat sink to the U800 chip with good
quality thermal compound and very secure mounting. It's larger then the
chip. It runs just over room temperature with the case on. I
measured it
with a type K probe through the vents and touching the middle of the
heat sink with a dab of thermal compound over a half hour or so time
frame.
I do notice mine drifts a tiny tiny bit on warm up, one or two mm to
the
left. It later snaps back about 1mm to the right.
Jeff
On 1/20/2013 2:00 PM, victor_j_silva wrote:
Hi Chip,
That was me! I do remember because you were very nice with the refund
even though I had left Pos FB already. Not many would do that.
I have seen three main failure modes on U800:
1. The trace shifts to the left (operator's left when looking at the
CRT) as the scope warms up, usually 5 to 10 minutes. These are the
ones I baked and revived!
2. The chip is very noisy, by this I mean there is a lot of jitter on
a very fast step response so that on every retrace the horizontal
position of the rising waveform will vary by 500ps to 1ns. Unlike a
good U800 which will show the retrace at the same position.
3. Outright dead.
The U800 you sold me was failure #2 type.
--Victor
--- In TekScopes@...
<mailto:TekScopes%40yahoogroups.com> ,
"random.path" wrote:
I sold an apparently working U800 to a list member from an old
2445.
Though the scope seemed to function just fine on initial testing, he
later emailed this back:
"I left FB after doing just a quick test at 1ms/Div. After more
testing I discovered that it is very noisy at 10X when time base is
faster than 5ns/Div after a quick 2 minute warmup. This Horz Amp is
not usable."
So I refunded his money. What I take this to mean is that the U800
can be failing or not meeting specs even without total failure. Just
something to keep in mind.
Chip
--- In TekScopes@...
<mailto:TekScopes%40yahoogroups.com>
, "victor_j_silva" wrote:
Sounds very much like the U800 issue.
About six months ago a posted about baking some U800s that had
failed this way and was able to rejuvenate them.
I put one of the U800s in a test scope and it's still working to
this day. I'm amazed.
--Victor
--- In TekScopes@...
<mailto:TekScopes%40yahoogroups.com>
, "cmjones012003" wrote:
Hello all,
I haven't posted to this list in a long time but have just been
lurking, I'm afraid.
[SNIP]
Thank you in advance
Chris
Cambridge, UK
--
