Tektronix SC504 Mini Scope Plugin - 80MHz - Dual Trace - Page 1
Forum section: electronics / repair

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 18, 2016, 03:28:17 am
content: I got a good deal on a "non-working" Tektronix SC504 scope. It was very dirty, missing the front shield that covers the tube (both a filter and protection for the user), and it had some broken knobs as well.I was able to clean it fairly well. The main bezel around the tube has some worn off paint I will likely sand and repaint.I was able to super glue the Volt/div knob for Ch1 after removing the broken piece of the shaft using a carefully bent coat hangar.I got a new blue filter/shield from Sphere. I also got a new knob pair for the intensity and focus controls.The fiberglass shaft for the focus pot goes all the way from the back out through the center of the intensity pot shaft (which is hollow) to the front of the instrument. This shaft had broken off at the tip, and there was nothing extending out past the end of the intensity pot shaft (which is hollow). With nothing sticking out there was nothing to which to mount a replacement focus knob. These knobs are on the top left of the unit face.See below for fix, but I cut the shaft and spliced it with some vinyl tubing. This let me slide the front part of the shaft forwards and back out through the hole to mount the new knob.There is an internal switch to switch between using the timebase vernier as a variable timebase like most scope have, or instead as a variable Hold Off. Someone had left the switch right in between the two settings which meant it would not do any horizontal sweep at all. I fixed this, and cleaned all the pots/switches as well.I am pretty excited to have this little 80 MHz dual trace scope working again. It even supports true X-Y!Here you can see the output of my recently restored Wavetek 145 20MHz Function/Pulse gen. The top trace is obviously a sine wave, while the bottom is the pulsed Sync output, which I am using for triggering. The scope also has an external trigger I could use instead, and a button that lets you view whatever waveform is being used for triggering.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 18, 2016, 03:30:42 am
content: Here is the fix for the Focus shaft. I essentially spliced it and extended it out to attach the new knob.The vinyl tubing appears a little stretched because I stretched it a tiny bit by pulling on the front half when I tightened the new knob on the front.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 18, 2016, 03:32:17 am
content: Side views.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 18, 2016, 03:34:12 am
content: Top and bottom views.Note the delay line wrapped around the CRT. Very compact!

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 18, 2016, 03:36:11 am
content: Here is the scope sitting in a Tektronix TM504 Mainframe. I have included a Fluke DMM probe for scale reference. It is a nice little unit.The mainframes take a whole host of Tek plugins, scopes, signal generators, pulsers, DMMs, Frequency counters, Digital Delay units, etc.In this photo you can see a basic 3MHz Function generator, the FG503, and a 4/12 digit 0.05% DMM the DM501A. The mainframe units come in sizes ranging from 1 slot to 6 slots.

author: setq
author_rank: Frequent Contributor
timestamp: September 24, 2016, 10:49:24 am
content: Nice work. Always fancied some TM500. Never appears in the UK for a reasonable price though, broken or otherwise.

author: rodd
author_rank: Regular Contributor
timestamp: September 25, 2016, 11:41:25 am
content: Hi,Very nice work!May I ask you how do you managed to clean the instrument so well?I bought a 577 curve tracer that has been left aside for a LONG time and needs a similar cleaning.Thank youSent from my SM-P605 using Tapatalk

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 25, 2016, 08:26:48 pm
content: Well, the interior was actually quite clean. It had a little dust on the top facing surfaces, but that was about it. I just went around with a Q-tip and IPA inside to get that dust cleaned up (after some canned air).For the outside I used Q-tips with some organic cleaner (some Target store product my wife bought... Method-brand something or another- natural glass cleaner. I believe it is one of those citrus based cleaners. I also used IPa with Q-tips as well.Here is a before photo from the eBay listing.

author: rodd
author_rank: Regular Contributor
timestamp: September 25, 2016, 08:35:06 pm
content: Quote from: FlyingHacker on September 25, 2016, 08:26:48 pmIn my case, the situation is reversed. The outside has probably been cleaned for sale, the the inside is like the outside of your instrument.I will try compressed air first, as you suggested.ThanksSent from my SM-P605 using Tapatalk

author: MarkL
author_rank: Unknown
timestamp: September 27, 2016, 02:44:30 am
content: Quote from: FlyingHacker on September 25, 2016, 08:26:48 pmWow - you should have posted that photo before!Nice restoration. Did you use anything special on the BNCs?

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 27, 2016, 03:47:14 am
content: Nothing special in the BNCs, yet anyway. I may take some contact cleaner to them, but they are working fine.