Uploaded December 2020 | Updated September 2026, 3 weeks ago
Since we now have a trace and the CRT looking really good, it's worth to dig into it further. In this episode we fix an issue with the 110V DC supply,... but it seems there is quite a bit more wrong with it.
We got a damaged Tektronix 475 for cheap, the seller stated that it was working before he sent it to the original buyer.
Apparently he tried to repair it, but obviously gave up at some point and decided to sell it as it is.
On first inspection, we found some damaged pot/switch in the timing circuit and a -8V supply short, but that was not all,... following was quite a lengthy investigation on some mysterious collection of faults. At the end, it turned out to be something rather simple, causing all the confusion and the strange behavior of the circuitry around the channel combiner circuitry.
It is also rather unlikely that it was in fully working condition before the transport damage happened as we found a power supply capacitor which was completely dead. Probably would still have displayed a trace, but the scope won't be really usable with that amount of hum on the supply..
On powering up after a brief safety inspection, the scope heavily distorted the camera audio.
This was either something wildly oscillating, or a hefty dose of X-rays. No trace was visible, only a brief dot in the center, confirming the CRT is most likely working and sweep does not work at all.
The scope is already back in working condition, you are invited to follow us over few episodes on the bumpy journey to success. ... so please stay tuned.
Part 1 is here
youtu.be/McfL-LA2DfI
part 2 here
youtu.be/iNI0eaQDvWQ
part 3 here:
youtu.be/h-a5STd3NVE
(c) 2020
dynoguy.co.uk
Since we now have a trace and the CRT looking really good, it's worth to dig into it further. In this episode we fix an issue with the 110V DC supply,... but it seems there is quite a bit more wrong with it.
We got a damaged Tektronix 475 for cheap, the seller stated that it was working before he sent it to the original buyer.
Apparently he tried to repair it, but obviously gave up at some point and decided to sell it as it is.
On first inspection, we found some damaged pot/switch in the timing circuit and a -8V supply short, but that was not all,... following was quite a lengthy investigation on some mysterious collection of faults. At the end, it turned out to be something rather simple, causing all the confusion and the strange behavior of the circuitry around the channel combiner circuitry.
It is also rather unlikely that it was in fully working condition before the transport damage happened as we found a power supply capacitor which was completely dead. Probably would still have displayed a trace, but the scope won't be really usable with that amount of hum on the supply..
On powering up after a brief safety inspection, the scope heavily distorted the camera audio.
This was either something wildly oscillating, or a hefty dose of X-rays. No trace was visible, only a brief dot in the center, confirming the CRT is most likely working and sweep does not work at all.
The scope is already back in working condition, you are invited to follow us over few episodes on the bumpy journey to success. ... so please stay tuned.
Part 1 is here
youtu.be/McfL-LA2DfI
part 2 here
youtu.be/iNI0eaQDvWQ
part 3 here:
youtu.be/h-a5STd3NVE
(c) 2020
dynoguy.co.uk
