McLarenblog

Grass Valley 200-1 Video Switcher

Problem: intermittent function.

Problem: After about 15 minutes of being turned on, the switcher lights would flash. The buttons would not operate but seemed to freeze the switcher. When I pressed a camera input such as camera 2 and this freeze happened, proper switcher operation would fail. I could press other buttons but they would only switch over to the new source when the button I pressed was down. When I lifted my finder the switcher would go back to camera 2. The toggle feature would not take place. After a minute or two the switcher would operate. As time or heat build up occured, the intermittents would seem to increase in frequency.

Troubleshooting: I checked the power supply voltages. Remember that this unit uses two separate power supplies. The service manual tells you how to check the voltages and note that the voltages indicated on the front of the the power supplies are not the exact voltages you should expect to measure. I plan on placing labels on the front of those power supplies with the exact documented voltages.

I reseated every card in the switcher frame.

I used a cooling spray on the suspected circuit board, the panel digital module, but I am quite careful not to freeze any component, only cool as I do not want to kill a component with drastic temperature changes.

Looking over the switcher flow diagram, the most suspicious board seemed to be the “panel digital module”. Go to book 1 and page 6-17 and go through the “control panel diagnostics”. I did this and everything came up looking ok on the diagnostic pod except when I got to “Function 10: CTL-STT REG”. The manual said to scope pin 7 of U11 and pin 9 of U10. The waveforms looked bad. The manual fails to show the correct waveform but digital pulses should, I would think, look similar to a square wave. Going on to “Function 13: PBUS RD STR” it told us to probe TP8 and gives an expected timing information. The width was ok but the recurring pulse was off. I was lucky to scope this test point when the switcher failed. The waveform looked awful. I had spikes where they should not be.

The pod failed to show any problem as this was a brief intermittent at times and the pod thus was not in a test mode at the correct moment to detect any failure. It was the oscilloscope that showed poor waveforms, like bread crumbs, leading me toward the problem area of the board.

Solution: About an hour before a class was to enter, I decided that some drastic action needed to be done, to get the switcher up and running. I noticed that every integrated circuit was in a socket. I had the switcher for over 8 years and we never reseated any IC chips. I turned the switcher off and waited about 5 minutes to allow the power to subside inside the unit. I used the wonderful tool that came with the switcher and pulled out and reseated each chip on that circuit board. The switcher came up and worked throught the first class with no problems. The switcher has been working for over three months now with no glitches. I went back to scope the test points that showed bad waveforms and found them greatly improved but not pristine. I plan to take my digital camera and shoot waveform images off the scope and put them in the service manual for future reference.

The information here is for educational and reference use only. Decide on your own how to proceed in performing any repair you face. We do not accept any responsibility for this information being entirely accurate. We hope it is accurate. Most of the information posed here has been noted to be significant, used in the repair process, and to some extent tested for accuracy through the actual discovery and recording of performing a repair. If you decide to use any of the information here, try to keep in mind that a number of factors may change when you attempt the “same” repair. Models do change from apparently being same units. Their are definitely different methods of making a repair. The steps that you should use to achieve a successful and expedient repair might be different. The problem you face with a piece of equipment might be similar but not an exact match to what we faced. Just use common sense and always be a bit skeptical of following our methodology until you feel that you and we share the same viewpoint and tactics.  

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