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Old 07-10-2021, 04:25 AM   #81
sam_sam_sam
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Default Re: Post your worthless and/or pointless repairs

Oh yea I do this crap when I do not have the right part sometimes double up capacitors back to back lay them down just to make it fit in the case sometimes it works sometimes it does not
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These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
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Old 07-26-2021, 01:46 PM   #82
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Default Re: Post your worthless and/or pointless repairs

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No there is nothing wrong with you > its manufacturer that use shit-e components that there is something wrong with them they are greedy and only interested in making as money as possible and giving the customer crap

I would recommend that when you recap something use well known capacitor brand manufacturers not some more of the same exact crap with different brands names
I meant why am I bothering to fix my ancient, decrepit PC instead of just assembling the parts I have sitting in boxes 10 feet away and have a way better PC?
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Old 10-12-2021, 09:07 PM   #83
lti
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Default Re: Post your worthless and/or pointless repairs

I tried to fit a different speaker in those computer speakers that smoked a long time ago. The sound quality isn't worth the parts cost (Peerless TC6FC02-04 drivers, on sale at Parts Express for $9.80 each) and the time it took for me to cut those adapters. They sound about the same as the original drivers, but with less bass. However, I haven't changed the driver in the left speaker yet, and the amplifier has a problem with weak bass in one channel that I never figured out.
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Old 10-12-2021, 09:52 PM   #84
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Default Re: Post your worthless and/or pointless repairs

^ Nice!

So wait, you bought those drivers specifically to fix these speakers? At almost $10 a piece, I can get a 2.1 system in good working condition around here. But I guess that was the point of your repair/exercise, wasn't it. Fits the thread pretty well.

As for the weak bass... I imagine that is likely caused by a bad cap somewhere - either electrically leaky or high ESR / low capacitance. If you swap the input signals going to each pin on the amplifier IC and the weak bass follows, the issue is before the amp in the signal circuit somewhere. And if the issue doesn't follow, then either bad output coupling or feedback cap in the channel with the weak bass. And if it's neither of those, perhaps the amp is bad. In that case, crank it up to the max and let it smoke itself out?? Bonus points if you use an adapter with voltage rated very close to the absolute maximum rated.

Anyways, that modded/repaired speaker looks totally badass like that. Love it!
.
.
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Unfortunately, I'm too cheap to spend any money when it comes to stuff like that... but NOT time. I posted this repair on a pair of cheap Acousitc Audio speakers a while back... and looking at it again, I certainly should have put it here in the worthless repairs thread.

So perhaps if you want to waste even more time with these speakers, you can try to rewind the old smoked drivers, if you still have them.

As for my more recent worthless speaker repairs... I did two speaker surround jobs: one on a single Boston HD8 speaker, and another on a pair of old and kinda crappy Philips speakers. Both of these were too cheap to waste money on surrounds... so I did them the same way I did my good ol' Realistic Nova-18 speakers: made the surround myself from paper. Though on that note, I should say I've improved the "quality" of my surrounds quite a bit. Seems that paper towel and latex house paint make for a decent surround material. Perhaps I should post pictures of these two with some details how to make them. The Nova-18 speakers were my first try... and they still work! I actually listen to / abuse those speakers quite often. They don't sound good, but there is something about their heavy speaker cones that produces a strong vibration in the chest and makes them sound 10x louder than they are. And being mid-range "bright", they actually sounds OK for everyday listening. Also, after all these years of me occasionally abusing them (cranking the volume to silly levels where the speakers distort... but still don't burn out for some reason), the paper surrounds have finally broken in to the point where they don't make any noise with high cone excursion (>5 mm each way). This is where the paper towel + latex paint helps on my "improved" versions, as that material doesn't need breaking in to get rid of surround noise. It's still an extremely lo-fi repair, though.

Last edited by momaka; 10-12-2021 at 10:27 PM..
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Old 10-13-2021, 12:41 AM   #85
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Default Re: Post your worthless and/or pointless repairs

Nice... I tend to bin small speaker enclosures with bad drivers, though I have repaired one speaker with bad tinsel wire... fixed with homemade tinsel wire...
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Old 10-13-2021, 12:47 PM   #86
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Default Re: Post your worthless and/or pointless repairs

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So wait, you bought those drivers specifically to fix these speakers? At almost $10 a piece, I can get a 2.1 system in good working condition around here. But I guess that was the point of your repair/exercise, wasn't it. Fits the thread pretty well.
I kind of did, but they can be reused for other projects. I'm curious to see if I can make small speakers that don't completely suck. Some companies have tried, but they just boost the "midbass" range into distortion (which most 2.1 computer speakers and all mini-stereo systems also do). Where I live, the only way to get computer speakers for $20 is to buy new, and everything in that price range is the kind of stuff that has fake reviews on online stores.

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As for the weak bass... I imagine that is likely caused by a bad cap somewhere - either electrically leaky or high ESR / low capacitance. If you swap the input signals going to each pin on the amplifier IC and the weak bass follows, the issue is before the amp in the signal circuit somewhere. And if the issue doesn't follow, then either bad output coupling or feedback cap in the channel with the weak bass. And if it's neither of those, perhaps the amp is bad. In that case, crank it up to the max and let it smoke itself out?? Bonus points if you use an adapter with voltage rated very close to the absolute maximum rated.
From what I remember, changing the input caps affected which channel had weaker bass, but the actual cap value didn't matter. It also doesn't affect headphones, which is strange. The headphone jack is connected to the main amp output with ridiculous 390 ohm series resistors. Maybe I need to get some more 100uF caps to see what happens if I swap the caps around the TEA2025B.

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So perhaps if you want to waste even more time with these speakers, you can try to rewind the old smoked drivers, if you still have them.
I thought about it.
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Old 10-13-2021, 02:08 PM   #87
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Default Re: Post your worthless and/or pointless repairs

Amplifier in those speakers a single ended (with dc blocking capacitor), bridge, or bipolar driver? Highly doubting bipolar but bridge is possible, else cheaper single ended...

Suspecting the bipolar and bridge configurations have better bass response that won't get eaten by the blocking capacitor?
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Old 10-13-2021, 07:36 PM   #88
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Default Re: Post your worthless and/or pointless repairs

It's single-ended.

Other configurations might still have a DC blocking cap on the input.

To make this even more pointless, I have some sound damping foam that I could stick on the inside.
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Old 10-14-2021, 12:43 PM   #89
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Default Re: Post your worthless and/or pointless repairs

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I kind of did, but they can be reused for other projects.
Good point!
Heck, making your own enclosures might give better results than the original plastic ones. Actually, weren't you the one that did that before? I remember a picture on BCN from quite a few years back with some home-made enclosures. I think it was yours, but don't remember 100%. Looked pretty cool, though.

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I'm curious to see if I can make small speakers that don't completely suck.
Probably.

I have a pair of slightly more "premium" stereo computer speakers from the late 90's, and they aren't too bad at all. They use 3.5" (or is it rounded to 4"??) "woofer" drivers going full-range, and a smaller set of 1" drivers for the tweeters. Branded "Saturn", model: SP-632A (and look similar to SP-622/SP-610/SP-5100/SP-500 series if anyone cares to look those up.) Based on a KIA6283k single-ended amp IC. They sound very decent, especially for close proximity listening, like they were intended for. Obviously not going to shake any walls with bass, but go down to 50-60 Hz range with relative ease and flatness in a small room. Some of the late Sony CRT TVs used very similar drivers, and they pumped out pretty good sound. Magnetically shielded too, so my CRTs approve!

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Some companies have tried, but they just boost the "midbass" range into distortion (which most 2.1 computer speakers and all mini-stereo systems also do).
Yeah, that is true.
A lot of the cheaper 2.1 systems have a dual-chamber woofer built with one chamber sealed and the other one ported. The "woofer" driver (typically 3.5-4" cone size) is positioned on the wall between these. Given the small cabinet sizes of these woofers, they have the typical double-humped response, with one peak in the 40-55 Hz range, and the other in the 100-120 Hz range. Their bass response also drops off very sharply below 40-50 Hz, depending on design.
So yeah, they do often have a boomy midbass, or at least very exaggerated low-end on voice content. Even then, though, these are still a lot more controlled than on cheap old ported speakers from the 90's.

The Realistic Nova-18's mentioned above are actually a prime example of that: they easily go +20dB (or at least sound like it) in the 70-80 Hz range, but drop off quickly below that. "One-note wonders", as some people call them. Of course, that's what happens when you couple a heavy, thick, paper cone with a 1" voice coil and a very weak motor (small magnet + large magnet gap): motor can't control the cone, and the cone does whatever it wants pretty much. Couple that with cheap shallow cabinets (check ), and it's an audio disaster... or a success, if you're trying to annoy your neighbors. Nothing like a thumpy bass going through multiple walls. Almost like taking a hammer and hitting on the walls.

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Where I live, the only way to get computer speakers for $20 is to buy new, and everything in that price range is the kind of stuff that has fake reviews on online stores.
I guess that's something I didn't consider. I live in a fairly populous suburban area surrounded by other similarly-sized suburban areas... so probably that's why. There's also always a lot of people moving in and out of this area, too (read: fairly good amount of yard sales and curb alerts when these people move.)

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From what I remember, changing the input caps affected which channel had weaker bass, but the actual cap value didn't matter. It also doesn't affect headphones, which is strange. The headphone jack is connected to the main amp output with ridiculous 390 ohm series resistors.
Well, the headphones wouldn't be affected, because they have a large impedance (typically 32 Ohms for most cans), in addition to those silly 390-Ohm series resistors. So even if one of the output coupling caps has gone down to 100 uF capacitance, you still won't notice it with headphones, because that sets the -3 dB low-pass cut-off point at about 4 Hz with those series resistors. But without those resistors and with an 8-Ohm or 4-Ohm load, the -3dB goes up to ~42 Hz or ~85 Hz, respectively for 470 uF output coupling caps (or ~20 Hz and ~40 Hz for 1000 uF caps, respectively.)

So if the output caps are bad (low capacitance and/or high ESR), that can really affect the -3dB cutoff frequency.

You can use this tool to see how the capacitance affects the -3dB low frequency cutoff for amps with DC blocking / AC coupling caps on the output:
http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

Quote:
Originally Posted by lti View Post
Maybe I need to get some more 100uF caps to see what happens if I swap the caps around the TEA2025B.
That too.

Quote:
Originally Posted by lti View Post
I thought about it.
You should.
Provided you can find thin enameled wire easily.
I suppose if you don't mind sacrificing a small DC motor, you can probably get some from there... or scrapped CRT TVs possibly (yoke and focus/pin coils.)

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Originally Posted by eccerr0r View Post
Amplifier in those speakers a single ended (with dc blocking capacitor), bridge, or bipolar driver? Highly doubting bipolar but bridge is possible, else cheaper single ended...
If the speakers are stereo and there is only one TEA2025 amp IC, it's a pretty sure bet it's going to be single-ended application (with DC blocking output caps.)

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Originally Posted by eccerr0r View Post
Suspecting the bipolar and bridge configurations have better bass response that won't get eaten by the blocking capacitor?
Yes... though if the output DC blocking / AC coupling caps are large enough, you will still get very good bass response.
As shown with the RC low-pass filter calculator tool above, 8-Ohm load with 1000 uF output cap sets the -3dB at about 20 Hz... which is pretty acceptable. Most of the time, the drivers and the enclosure will be the limitation with such small speaker setup, rather than the output caps... especially on tiny speaker drivers that really can't go down below 50-60 Hz anyways. Might as well block those lower frequencies from going into the driver and wasting power unnecessarily... which could matter in a positive way if the power supply is undersized, as is typically the case with very cheap desktop speakers.

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To make this even more pointless, I have some sound damping foam that I could stick on the inside.
LOLz.
Actually, the most that will happen from doing this is you might dampen some cabinet resonance/vibration, especially if the enclosures are rattly and cheap. If it's a ported design, though, generally damping will make you loose a few dB (at least with larger speakers... not sure if there would be a difference with small desktop speakers like this.)

Last edited by momaka; 10-14-2021 at 12:47 PM..
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Old 10-14-2021, 11:31 PM   #90
lti
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Default Re: Post your worthless and/or pointless repairs

Quote:
Originally Posted by momaka View Post
Good point!
Heck, making your own enclosures might give better results than the original plastic ones. Actually, weren't you the one that did that before? I remember a picture on BCN from quite a few years back with some home-made enclosures. I think it was yours, but don't remember 100%. Looked pretty cool, though.
That was me.

Quote:
Originally Posted by momaka View Post
I have a pair of slightly more "premium" stereo computer speakers from the late 90's, and they aren't too bad at all. They use 3.5" (or is it rounded to 4"??) "woofer" drivers going full-range, and a smaller set of 1" drivers for the tweeters.
The original drivers in these speakers were about that size (92mm outer frame diameter). I was thinking about something that would beat those really expensive Bose computer speakers. There are some Tang Band speaker modules that might do it, but I don't feel like paying that much (close to $70 for a pair).

Quote:
Originally Posted by momaka View Post
A lot of the cheaper 2.1 systems have a dual-chamber woofer built with one chamber sealed and the other one ported. The "woofer" driver (typically 3.5-4" cone size) is positioned on the wall between these. Given the small cabinet sizes of these woofers, they have the typical double-humped response, with one peak in the 40-55 Hz range, and the other in the 100-120 Hz range. Their bass response also drops off very sharply below 40-50 Hz, depending on design.
So yeah, they do often have a boomy midbass, or at least very exaggerated low-end on voice content.
The really cheap ones have a simple ported enclosure with what looks like a toilet paper tube as a port. One example that I have personally listened to is the Cyber Acoustics CA-3602. On those, turning up the bass control just makes speech impossible to understand, and the bass response drops off at about the same frequency range as the old Dell / Harman Kardon 2.0 speakers like the HK-206.

Quote:
Originally Posted by momaka View Post
You should.
Provided you can find thin enameled wire easily.
I suppose if you don't mind sacrificing a small DC motor, you can probably get some from there... or scrapped CRT TVs possibly (yoke and focus/pin coils.)
I didn't spend much time looking for wire, but I don't think I have anything in my scrap pile with thin enough wire.

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Originally Posted by momaka View Post
LOLz.
Actually, the most that will happen from doing this is you might dampen some cabinet resonance/vibration, especially if the enclosures are rattly and cheap.
These are cheap, but resonance is less of a problem with the new drivers. Putting damping material in modern $10 speakers would be even more pointless, although the set I have sounds better with the speakers in free air than with the speakers inside the enclosure.
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