Re: Tek 2215

Tothwolf
 

On Mon, 25 Jan 2016, David @DWH [TekScopes] wrote:
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.
I didn't notice any cracks in the coating of those resistors in my 2213 scopes. All 3 of my 2213 scopes have those 4 resistors mounted close to the board so I'm wondering now if I should replace them and space them away from the board. B0233xx in the photo above got a lot more use than either B0228xx or B0229xx and the board under those 4 resistors is just starting to discolor.

I initially only had the CRT out of B0233xx so I could replace the damaged front bezel.

I've been using Richco CER-6 ceramic spacers (~$0.073/ea) to space these type of components off the board (pointed end goes towards the board). I also used them on the preregulator boards when I replaced R911, 150K 1W carbon comp. The replacement metal oxide resistor in the photo below is actually a 2W part even though it is physically smaller than the original.

http://strudel.ignorelist.com/~tothwolf/photos/Tektronix_2213/Tektronix_2213_2/1600/IMG_9112.1600.jpg

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
These are the resistors you used in your scope? I'll add these to my notes to consider later when I finally get back to working on the 2213s.

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