Thursday, 1 May 2014

Tektronix 2225 Repair

Filed under: Uncategorized — Michael @ 16:24

Among my various pieces of old test gear is a Tektronix 2225 oscilloscope. This is a very capable 2-channel, 50MHz scope from the late ’80s. I bought this off eBay some years ago and was pleased that it was in near perfect working order. The only problem was that the exterior was quite dirty and the front panel potentiometers were very noisy. After a good clean, it looked good but the pots were still a problem. Even so, I use it regularly and always thought I would get around to pulling the front panel board someday and give it a good alcohol bath. Then, a couple of weeks back, I stumbled across a web-shop that sells old Tek parts. And they had a front panel board for the 2225! The shop is www.qservice.tv and they have tons of stuff for all kinds of old gear, not just Tek. The price was very reasonable so I ordered the board and received it within a couple of days. And they even guarantee it for a month!
Now, with a ‘new’ front panel board in hand, I got down to the repair. Following the instructions in the service manual, it went smoothly. It required removing the attenuator board and then the front panel board. Here’s a shot of the ’empty’ scope.
IMG_0001

Here is the stuff that came out. That’s the attenuator board on the left.
IMG_0002

One thing that required some effort was transferring the seven ribbon cables from the old board to the new one. (A recently acquired vacuum desoldering station was a big help.)
IMG_0003

Once the boards were back in, there was a small amount of re-wiring. Since the AC-GND-DC switch on the front panel board is ‘between’ the BNC connector and the attenuator there’s a few resistors that needed to be soldered in place and ground wires reconnected. The resistors are standard values and I just replaced them with new ones.
IMG_0004

Here it is all back together.
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And, it works! Even though the ‘new’ board was removed from another scope, it’s a huge improvement over the original controls and was well worth the cost of the board and effort to install it.
Long live the 2225!