开云体育

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Phillip Potter
Sent: Sunday, March 03, 2019 7:46 PM
To: [email protected]
Subject: Re: [TekScopes] Help with 7A18 problem

Hi Bill,

No... There was nothing that I wrote that I think is wrong. It was a matter of timing. I hadn't read all of the other replies, especially the one where you found the attenuator pin issue!

I felt that my reply was badly timed and didn't add to the conversation. I did, however, tear my 7A18 down and clean the switch fingers with IPO, and got it all back together; whew! So, from that aspect, it was ok.

I hope that I haven't led you astray or been a bad influence, Bill...
and I wish you the best with your amplifiers!

Phil

On 3/3/2019 2:31 PM, Bill Carns wrote:

What ?? Now confused. Was there something wrong with your first reply?

Bill

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Phillip Potter
Sent: Sunday, March 03, 2019 3:46 PM
To: [email protected]
Subject: Re: [TekScopes] Help with 7A18 problem

Please disregard!!!

Sorry,

Phil

On 3/3/2019 1:38 PM, Phillip Potter wrote:

Hi Bill,

I have the same amplifiers and when I first got them, had the same or
at least similar issues.

I tore them down, one at a time, and soaked 24lb bond with IPA, to
clean those switches. Yes, they are a bear to get to! IIRC, I had
to disassemble them down a ways to get into them. There were shields
on the inner sides and on the outer sides, too. Once I had them
broken down, it was a simple thing to get the soaked paper into the
switch fingers and carefully pull it through, in the same way that a
turntable moves a record under the stylus... never backward!

I recommend doing this somewhere where you can leave it laying,
disassembled, so that you can see how you got it apart, making it
easier to reassemble it. I took pictures on my phone at each step of
the way. It was a "trick" of a deal getting it broken down to the
point where it could be cleaned, however. Pictures helped me to stay
on track and get it all back together! Tektronix did it's homework...
they were made to be repaired... gotta love 'em!

I hope I've inspired you and not the opposite. I did have to work up
my nerve to tear into them, but the result was two operable
amplifiers, I am glad that I took my time and worked carefully.

Phil

On 3/2/2019 2:26 PM, Bill Carns wrote:

I'll have to go put the unit back in the mainframe and investigate
but my memory says that most were bad.

I have investigated more and remove the upper capacitor cover and,
boy are those things hard to get at. Gonna be real hard to get
cleaning paper in there on all the switches. Some are not bad,
others really bad to get to. One set has an additional little cover
over them for some reason.

Working on this thing is not for sissies.


B

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Albert Otten
Sent: Saturday, March 02, 2019 3:53 PM
To: [email protected]
Subject: Re: [TekScopes] Help with 7A18 problem

On Sat, Mar 2, 2019 at 07:58 PM, Colin Herbert wrote:

---
On the subject of the input attenuators, they are the type which
are operated by cam-switches. They have springy gold-plated
contacts that get moved up-and-down by cams on the controls shaft.
The circuit board that they are on has gold-plating, too, and the
board itself is made of an easily-damaged material. You need to use
thin strips of paper moistened in IPA and trapped between the
moving and stationary contacts, they *gently* pulling the paper
strip out. You may have to do this a few times. Don't use any other
solvents or contact-cleaner as you will probably ruin the board. Of
course it may only be one or two of these contacts that is dirty,
as has already been suggested; there are only four attenuators
there - they get switched in-and-out to get the different VOLTS/DIV
settings. In the most sensitive VOLTS/DIV setting, they are all
switched out, so if your 5mV/div setting shows lousy bandwidth,
then it is likely to be caused by some other problem, not just the
attenuators and their switching . Of course, there might be a
problem there, too, but it won't be the only one.

Hi Colin,

You probably were too quick in your statement about the 5 mV/div
setting. In that setting all attenuators are bypassed by means of a
series of closed contacts, so any dirty contacts there destroy the
signal path.
I'm not sure about the 7A18 construction. My impression is that
including AC/DC there are 10 contact pairs above the drum and 10
below the drum. (Each contact pair forming one switch).

It would still be nice to hear from Bill which V/div settings are
good and which are bad.

Albert