Re: Tek 2215

 

On Mon, 25 Jan 2016 01:36:53 -0600 (CST), you wrote:

On Mon, 25 Jan 2016, David @DWH [TekScopes] wrote:

There was another resistor change Tektronix made and I think it was for
reliability. The 2213 and 2215 use two 1/2 watt 1% metal film resistors
in series for the collector loads at the output of the vertical
amplifier. These resistors run hot making them unreliable and were the
first 2213/2215 repair that I made and I know of two other instances
where they had to be replaced. The later models used 3 resistors in
series for each collector load to distribute the heat better.

The collector load resistors are not difficult to replace so I would
change them also.
Are those the 4 resistors mounted to the board plus the two inline with V+
and V- on the left side of the board in this photo? One of my scopes has
one carbon comp and one carbon film for the two inline resistors. I'm
planning to replace the two inline resistors with Vishay CCF6015R0FKE36
and the 18K R877 with a Vishay CCF0718K0GKE36. I hadn't planned to replace
the 4 resistors on the board, but they look like they might be 1W parts.
I've seen photos of these boards where the board is discolored badly from
heat around those 4 resistors.

http://strudel.ignorelist.com/~tothwolf/photos/Tektronix_2213/Tektronix_2213_3/1600/IMG_9288.1600.jpg
Sorry for taking so long to respond. Those are the ones.

The parts list says they are 1/2 watt 1% film 340 ohm resistors (and
metal film based on the part number) and since there was only one
modern choice matching that available, I was not picky. I bought 10
from Mouser, replaced the 4, and left the remaining 6 inside a bag
taped to the inside of the chassis with a note.

The originals in my case were visibly discolored and cracked and once
removed, their coating flaked off. I was able to replace them without
removing the CRT using needle nose pliers. The original parts were
spaced above the printed circuit board so I used the shaft from a
Q-tip as a temporary spacer during installation.

The replacements were physically smaller than the original parts. I
thought Tektronix might have selected the originals for good RF
performance but other than size, they are the same series of film
resistors used throughout the rest of the oscilloscope and a transient
response test showed that the new physically smaller replacements
worked fine.

I did not check it before since I did not have more than one resistor
to select from but the Dale MFF series datasheet says "very good high
frequency characteristics" for whatever that is worth:

http://www.33audio.com/enter/data/DaleFilmpart2.pdf

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