Well, my trusty 9-90 test display has decided to stop working last week. Now both standards display a blank raster with sound. No snow any more on UHF either.
Before opening it up are there any known issues around this fault, its been as good as gold for years, even more so with me using on a daily basis for the Hedghogs. I do not have the schematic presently as i know Chris has the library down in request only.
Things have got worse, decide to turn it on again for first time since last week and had nothing at all. Removing the back and a few checks reveals the mains fuse has blown, and the 240 volt primary is now open circuit !
115v tap is still ok
I do wish manufacturers of the time fitted a fuse between the rectifier and the transformer secondary, not that the rectifier has been tested yet.
Connecting the chassis to the bench supply, it is drawing 1.1 amps @ 13 volts but still blank raster on all standards.
Fret ye not, Stephen: I have far more of these than is sensible, so I'm quite happy to break one for spares for us.
I haven't forgotten about the GEC, by the way!
I had one where the rectifier failed and killed the transformer. I replaced it with a small switched mode. Rare to have anything on this set fail though I would think. I also have a service manual, where someone had written some notes about line output transistor failure.
Managed to get an hour looking at the for the lost video signal, chased it all the way through onto the 3rd IF transformer where it disappears.
It is looking green around its pins which may point to the dreaded green spot corrosion again. Wonder if that's what took out the mains transformer.
Speaking of which, it was peeled to check for green spot near the terminals and none found. The primary measures 1.3 megs now.
It seems a cleverly designed transformer with double pole windings that does not emanate magnetic flux outwards to interfere with the CRT. I'm not an expert on this so could be totally wrong.
Could be the transformer has an internal thermal fuse....
I did find a internal glass fuse !, it had not failed.
Been persisting with Hedghog testing using the 9-90 inputting 405 using a lead to the video drive transistor through C504, this produces a nice clean image as you would expect.
Whilst doing this noticed C509 had been visibly leaking. It is a 10uF 100volt on the Cathode of the CRT. Testing on the Hunts CRB3 showed leakage at 30 volts.
Well worth keeping an eye on if you have this model.
Hope to get the IF strip sorted soon as Cathovisor Mike has very kindly offered a donor set.
Hopefully with UPS on Friday, Stephen 👍
Quick update - it's all packed up and ready to go. It should be with you on Monday.
Thanks to Mike`s donor set, my original is back up and running very well again. Now to meet the Christmas rush of Hedghogs.... all good fun 😆
Now to meet the Christmas rush of Hedghogs.... all good fun 😆
Shouldn't they be hibernating by now? 😊 😑
To understand the black art of electronics is to understand witchcraft.
They are reproducing nicely 😱
Glad it got your set up and running again, Stephen. Now, I suppose at some point I ought to turn my attention to my CVM-90... and the other three TV9-90s!!
I meant to mention, following on from my earlier observation about no fuse in the secondary side of the mains transformer.
It struck me that the solution was to use the fuse holder already present in the set if used on 110 volts (never going to happen). I snipped the 110 volt wire connecting to the transformer and the adjacent link on the fuse holder, then reconnected the fuse holder to the AC output side, thus protecting the transformer from any overload on the output including the rectifier.
Its got an 850mA slow blow and runs fine.
Both my examples draw about 900mA at 12VDC powered externally. My notes show this was TCF on 625 with tone! No note of draw on 405.
This is making me think a 1A fast blow is the best option for when I get my two examples working.