开云体育

Hi.

I have this 492 which was working.

Last week a friend donated a largely stripped 492 whose remaining parts I thought could be tested in the working unit.

First thing to test was the crt.
Unfortunately, nothing appeared on the display and the distinct smell of toasted component filled the air so quickly turned the 492 off.
Following my nose, led me to the video amplifier board, where a shorted tantalum was quickly found.
With that replaced, the 492 came back to life, all the lights, traces, display readings etc. However, there appears to be no vertical readings.

Before I dive into the manual when I next get time, does anyone have any idea as to where to look? For example, could the video board have damaged an adjacent board?

I've seen people replacing the diode and tantalum in the Yig filter, so I should just check there first...

Once this is fixed, I'll give it a miss testing the remaining parts and just sell them 'as is - for parts'


James

James,

I do not know if the 494XX type is the same or not in its guts. This site may help: . Page 9 may be of help. The resistors he mentions should be increased to 2W (15mm length or longer). A 1 or 2% tolerance would be even better than original. Keep looking for bad tantalums, you may fine more.

Mark

Hi Mark,

thanks for the link. I'll have a good read through it. As for further failed tantalums, that could well be the case as the video amplifier is still not running correctly. Fortunately the 'parts-donor' unit still had this module and that one does seems to be working.

I've removed the Yig and have been looking for clearer disassembly images or videos but without luck as of yet. Before I attempt to open it, when I get some time, I'll look through the manual and see if the lack of vertical deflection might be on one of the plug-in boards.

There are 11 of the bolt-connected modules, from the underside, which I had intended to test, but I'm not prepared to risk any further damage.

Thanks


James

Hi again.

To finish off this thread.

For whatever reason, the 'spare' CRT damaged the video board, revealing that the CRT is dead and may well have been why the 2nd 492 had been stripped down so much.

In the end I didn't open up the YIG, as I was unable to locate any clear images so I focused on the LV rails (which is where I should have started in the first place). The +9v rail was reading +1.26v and the +9v rail 2A fuse was open.
One thing that had also changed following the failed CRT test was that the scale illumination no longer worked.
Swapping around the multi-pin illumination connector situated behind the CRT bezel resolved that problem, resolved the blown fuse and also resolved the lack of vertical deflection.

With the unit fixed and working again, I packed the SA away and have now passed it on.


The End.



James