Today I decided I would focus on it again since I know the functionality of the others. I started it up, but I was in the garage this time. It shut down after about 5 minutes. I turned it on again, and this time I set up a CPU 12V fan to blow directly in the area behind the front panel (The cabinet is off). It stayed on around 25 minutes this time and then turned off again. That was about 30 minutes again.
A 12V CPU fan is not enough airflow! When I work on these scopes, I use an 18" diameter fan of the type that you would use for cooling a room, like this one: http://www.homedepot.com/p/Lasko-Cyclone-18-in-Adjustable-Pedestal-Fan-1823/202563946
I have it blowing in from the right side of the scope. The right side of the scope I keep lifted about 3 inches, which helps to cool the power supply as well.
As far as which trigger chip is bad, look for discoloration on the pins and package that may indicate which one is bad, if you're lucky.
@AndyC_772 @Jwalling Yeah I found out about the case/airflow situation a few minutes after the unit shut down initially. And I will also take a look at the chips again under my microscope. To be honest, I'm not entirely sure that the heat issues aren't due to Friday being a very hot day, and that could have caused the problem mainly. Yesterday was fairly cool, for Houston, Texas anyways. I turned the scope back on last night and left it on overnight and it's currently on now. It hasn't turned of at all. During the time, I have ran 20 SPC manual test an it has passed every one. I won't be able to check anymore results until I receive a probe that will work with the scope. This being the case, I'm going to have to set it aside and look at some of the others I have to work with that have smaller issues I should be able to repair (784A, 744A, and a 724A. I also have 684C, 544A, and another 744A, but they have power on issues and they will be my training scopes).
Now, a bit of advice from you guys who have worked on the TDS5XX, 6XX, 7XX series of scopes and any other high BW scopes, if you don't mind, but first let me explain my situation a bit better so that you will understand where I am and what I'm going to do.
I'm currently a fresh EE student (new career switch at 43, just started from scratch fall 2016. I graduated from school the first time in 1996, so I decided to go through the whole process again
), and I'm footing the bill for school. I plan to repair, calibrate, and restore/refurbish oscilloscopes as a side business to pay for school, plus I just love test equipment. I purchased these scopes (and 2 others which should arrive today, Tek 7154B, 644B) as a start. With this in mind, here are my questions to you:
1) What standard set of tools/test equipment do I need to perform what I want to attempt? I have a function generator currently that I use for waveforms, but I'm currently looking for a signal generator, and a high current probe for my Fluke 87V which should be here this week.
2) What scope should I use as a daily driver for this type of work and what type of scope should be my specialty scope (which is why I was thinking about keeping the 694C. I actually have a Tek TCP0030 High current probe coming as well this week. I was planning on using them in tandem if that would work, but now I'm not sure about keeping the 694C after hearing about the trigger chips and overheating issues)?
3) In your opinion, is the 694C worth the trouble of fiddling with, or should I just sale it as is and move on? The scope seems very solid other than the issues I have spoke about and it has the 1M option for the extended memory. I have to make money so I can't afford to waste time on equipment that would be better suited sold as is. I do, however, want to become very good with scope repair and I know the challenging jobs are the ones where I grow the most, but there is a cut-off point.
As usual, I really appreciate the guidance