Re: Part needed for Type 576 Curve Tracer


Mlynch001
 

Craig,

That is an awesome way to get one of these. I feel like I almost hit the jackpot when my Flea-Bay bid won at $255. Mine looked great and even had a bright "spot" that showed in the pictures, so I was 95% certain that there was a good CRT in the machine. After it arrived in ONE PIECE, I might add, First thing I did was open the manual and started checking the power supplies. To my relief, everything was almost spot on, EXCEPT the 5V, which was quite low at about 3.81V. So I knew that was the first order of business, going forward. With the power supplies mostly good and a bright controllable spot, I knew that most of the machine was working, In addition, I was able to get the spot to move, but could not center the spot on the screen horizontally. I pulled all the Transistors from the display board and, by luck, the first one that I tested (Q660) was a resistor. I replaced it with a 2N3906 and that made it possible to center the spot, but still no trace or step generator. After a lot of searching, I found a fellow who described symptoms almost exactly like mine had with the 5V, so I started by looking at C759, Which was the cause of his issue. My C759 was supposed to be 11KuF and tested at 89uF with an ESR of something like 10 Ohms. Curiously, this cap had already failed once before and had been replaced with a 14K uF 25V TEKTRONIX Part with a 1992 date code. I have a hobby of "restoring" these large aluminum caps so that the machines appear to be original. So I order the appropriate modern cap and "Restored" this one, it looks and fits just like the original. So I think I have this one closer to working. I fire her up and the 5V rail has come up to about 4.1V, but still low and with a lot of current draw @ 440 mA. So I know that I have ANOTHER bad cap. More to follow.

--
Michael Lynch
Dardanelle, AR

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