- Scope keeps blowing fuses - 3 Updates
- Radio Shack Weather Cube - 3 Updates
| Cursitor Doom <cd@notformail.com>: Oct 22 03:26PM +0100 Hi all, So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing main fuses (the 2A one on the rear panel). I opened the case and found two RIFA caps that had obviously blown, so replaced them, but it's still blowing fuses. I can't be 100% certain, but I'm pretty sure there's a fault with the PSU board as I get the briefest whiff of burning from that area each time I put a new fuse in and power up. The new fuse blows again before I get to see any smoke coming from anywhere at all. I'm linking to a diagram of the PSU as I'm not familiar with this circuit topology. If anyone can spot a component here that could have gone low-resistance and might be a good candidate for out-of-circuit testing, by all means let me know. Thanks, CD. https://disk.yandex.com/i/UhxATIy-6Y0LIA |
| "Peter W." <peterwieck33@gmail.com>: Oct 22 08:08AM -0700 Did the caps fail Open or Short? Peter Wieck Melrose Park, PA |
| "ohg...@gmail.com" <ohger1s@gmail.com>: Oct 22 08:57AM -0700 On Saturday, October 22, 2022 at 10:26:11 AM UTC-4, Cursitor Doom wrote: > Thanks, > CD. > https://disk.yandex.com/i/UhxATIy-6Y0LIA Did you do any resistance checks like for a shorted rectifier(s) or power transistor like Q1050? FWIW, installing a new fuse and waiting for smoke is a terrible idea. |
| John Crane <john_crane_59@yahoo.com>: Oct 21 07:41PM -0500 Bought one in excellent shape. Worked great for about a month, then developed a buzzing background noise in the audio - but you can still hear the weather reports. Just annoying. It's been sitting on a shelf the whole time. And 9V battery powered. I tried replacing all the electrolytic caps, but no go. In fact, the buzz is slightly louder. Any ideas as to what could cause this? |
| Jeff Liebermann <jeffl@cruzio.com>: Oct 21 08:34PM -0700 On Fri, 21 Oct 2022 19:41:26 -0500, John Crane >I tried replacing all the electrolytic caps, but no go. In fact, the >buzz is slightly louder. >Any ideas as to what could cause this? Does the buzzing follow the volume control? In other words, does turning the volume up and down change both the weather report AND the buzzing, or is the buzzing a constant level? The problem might a new source of EMI (electromagnetic interference). Try moving the cube around the house and see if the buzzing gets stronger near some new electronic or motorized equipment. Also try moving the cub outside and down the road to see if it goes away with distance. I once had a weather cube. I found that nearly dead 9V batteries would cause the audio state to "motorboat". It was easier to replace the battery than the fix the problem, so I never troubleshot it down to the failed component. I suspect you might have a similar problem if you're using a rechargeable LiIon 9V battery, some of which only produce 7.2VDC. If you have a new 9V alkaline battery, try it. -- Jeff Liebermann jeffl@cruzio.com PO Box 272 http://www.LearnByDestroying.com Ben Lomond CA 95005-0272 Skype: JeffLiebermann AE6KS 831-336-2558 |
| John Crane <john_crane_59@yahoo.com>: Oct 21 11:01PM -0500 On 10/21/22 10:34 PM, Jeff Liebermann wrote: > to the failed component. I suspect you might have a similar problem > if you're using a rechargeable LiIon 9V battery, some of which only > produce 7.2VDC. If you have a new 9V alkaline battery, try it. The buzzing follows the volume control, it's not constant. Moving it around the house doesn't affect the buzzing. It stays at a constant level. And no new equipment came online in the house since it's been in use. My battery was a Duracell alkaline at 8.59V. I replaced it with another Duracell at 9.19V. No change in the buzzing. Really a strange problem. I'd suspect a bad connection somewhere, but the problem just appeared slowly as it was used on a shelf. There was no movement, or jarring involved that could have knocked something loose. And there is a lot of wax poured over the components - presumably to keep the little coils fixed in shape. I thought the electrolytics finally gave out, as it's a vintage one with faux wood grained sides. Maybe 70's - 80's era. |
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