I mended that!! (post your fix! mods/hacks welcome!)

[MrWizard6600]

Show off your hardware fix!

So I was on my way to home depot to grab some electrical tape for a quick speaker wiring fix (simple loose connection), and it got me thinking, in all the years I've been on these boards I've never seen just a fixed stuff thread. A thread that just contains pictures of a clever (or not-so-clever) fixes for hardware problems.

I've got two that I'll post here:

simple speaker fix: The volume control (a simple potentiometer) had some kind of loose connection. For the past couple months You'd have to orient the control in such a manner to get it working, but recently it has been completly impossible to orient correctly. Realizing that it was just a loose connection, and that buying a new pair of speakers all together over something that stupid is entirely retarded, I got to work ripping apart the little nob to see if I could fix it:

The other thing is my now dead ipod nano. 8 months after this fix the thing started making wierd electrical noises, but still, i got those months back out of what would have been a useless nano. OK so, like alot of people who bought an ipod nano, the hold switch died in the "hold" position, meaning my ipod was unusable. Sometimes when i flipped it to the regular position allowing the ipod to respond, it would switch on and off sparatically making the thing useless.

So I unscrew the PCB from its little standoffs:

the hold switch just popped right out. No resistance at all. Useless. There were five (tiny, these are some of the smallest solder points I've ever seen) contacts holding the switch to the PCB. A little bit of googling revealed that two are just for support, one is a supply and the two others are returns for closing the "hold function on" circuit, and the other for closing the "hold function off" circuit. Using some basic logic I came up with the two contacts near the left side of the ipod were the two for the "hold function off".

So, all I did was a pencil mod! I tried to get a shot but the camera wasn't anywhere near powerful enough for a macro shot like that.

Rather alarmingly the ipod turned on right in my hands after getting the hold function turned off. With it on there was nothing I could really do to get the ipod turned off, so I was a little worried about a small current giving me a little shock, and my fingers did tingle, but the thing powerd up normally right in the middle of the podcast I was listening to:

 

[gwarren007]

doesn't this go in ther "getto mod" section?

 

[engiNURD]

doesn't this go in ther "getto mod" section?

LOL

 

[MrWizard6600]

doesn't this go in ther "getto mod" section?

lol, I'd be a whole lot more intrested in a dedicated section than a little thread, but until we get a ghetto mod section, I'll take this!

and speaking of things that need mending, dont evern install punkbuster...

ever.

 

[Mohonri]

I opened up our TV and soldered a resistor from the s-video inputs to GND, so that my HTPC would always sense the TV. Without that mod, the HTPC only sees the TV if the TV is switched on.

I was taking pictures up until just before I actually soldered the resistor in place, so I unfortunately don't have a pic to post. And I'm not about to crack open that beast again to take a pic.

 

[BrainEater]

I opened up our TV and soldered a resistor from the s-video inputs to GND, so that my HTPC would always sense the TV. Without that mod, the HTPC only sees the TV if the TV is switched on.

That is a damn good idea.

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I run a pair of viewsonic VX922 19" LCD monitors on my main rig.....about 30 hours past the warrantee , one of them started to 'not-come-out-of-standby'.....

After some reading on the 'webs , I found the issue : bad capacitors on the monitor psu.

Sure enough :

-----

Capacitors replaced , faulty units in front :

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Works good as new .....and right on schedule , my second monitor went , same problem.It's been fixed too.

The problem was'nt 'bad' capacitors per se , but caps spec'd right on the limit.I replaced them all with higher voltage units.Quite an amazing job of spec'ing them to fail *right* after the warrantee's expire.heh.

 

[MrWizard6600]

nice job, glad it works. Those oxide caps really are useless when it comes to precision capacitence. If you guys look most of what are there are a couple hundreds micro farads, generally speaking they give you three digits. "470uF" or "100uF", but infact you'd be luckey if that was (470 +/- 200)uF. So when your working with these caps (which cant be applied to anything other than line regulation because they're so grossly inaccurate), its standard procedure to over-build the needed capacitence by as much as 100%, which it sounds like viewsonic didn't do.

but anyways, hows the back of that PCB look? I'm horrible with a soldering iron, usually I can get it done but I'm still terrible at finessing that crap into where it needs to go.

 

[gee]

The problem was'nt 'bad' capacitors per se , but caps spec'd right on the limit.I replaced them all with higher voltage units.Quite an amazing job of spec'ing them to fail *right* after the warrantee's expire.heh.

I see CapXon. They made a bunch of bad capacitors (part of the taiwanese bad cap scandal, along with Fuhjyyu annd other makers) with an incomplete electrolyte that create hydrogen gas and bulge. And that's what you've got there.

When you replace these capacitors, make sure you get ones with a equivalent or better ripple current rating, 105C temperature range and similar or higher voltage rating. Don't mess with the capacitance, and try to get a capacitor which has a similar ESR spec as the old one - power supplies are compensated based on the output capacitor specifications, and putting a substantially different capacitor on the output (eg. a polymer cap) can make the thing go unstable and destroy itself.

I tend to use Nichicon PW's for repairing power supplies.

 

[Mohonri]

I run a pair of viewsonic VX922 19" LCD monitors on my main rig.....about 30 hours past the warrantee , one of them started to 'not-come-out-of-standby'.....

After some reading on the 'webs , I found the issue : bad capacitors on the monitor psu.
...
Works good as new .....and right on schedule , my second monitor went , same problem.It's been fixed too.

Speaking of fixing monitors, I've fixed a fair number of Dell 17" monitors (usually E172FP_). The issue comes from bad solder joints, which eventually fail and end up burning out the transistors on the backlight inverter. Replace the transistors, resolder the transformer leads, and it's good as new.

nice job, glad it works. Those oxide caps really are useless when it comes to precision capacitence. If you guys look most of what are there are a couple hundreds micro farads, generally speaking they give you three digits. "470uF" or "100uF", but infact you'd be luckey if that was (470 +/- 200)uF. So when your working with these caps (which cant be applied to anything other than line regulation because they're so grossly inaccurate), its standard procedure to over-build the needed capacitence by as much as 100%, which it sounds like viewsonic didn't do.

but anyways, hows the back of that PCB look? I'm horrible with a soldering iron, usually I can get it done but I'm still terrible at finessing that crap into where it needs to go.

Desoldering braid is your friend. It soaks up the solder and leaves nice clean holes.

In general, I've found that when speccing electrolytic caps, as long as you meet or exceed the voltage rating and capacitance, you're in good shape. The only application where you need more precise capacitance is in timing applications, and you never see electrolytics used there. For that kind of application, it's always ceramics and occasionally poly film caps.

gee, I've been studying switchmode power supplies a lot lately (and taking a lot of them apart), and I haven't really seen any sign of the power supply being compensated for the capacitance. Can you show me an example?

 

[Crispy002]

Bought a broken 32" Westinghouse for $10. Replaced 4 broken backlights and a fried transformer, sold for $250. I repair tvs/monitors periodically for extra fun money. Got a few more to fix up before I can get a 5870.

 

[gee]

gee, I've been studying switchmode power supplies a lot lately (and taking a lot of them apart), and I haven't really seen any sign of the power supply being compensated for the capacitance. Can you show me an example?

Grab a copy of the Abraham Pressman power supply book (aka the 'bible'), there's a whole chapter on compensation. Compensation strategies are different based on whether the supply operates in voltage or current mode. I'm a bit rusty on compensation (haven't done an offline supply in a couple of years) so this could be a load of baloney:

In voltage mode supplies, the output inductor and capacitor create a low pass filter, and corresponding double pole. Changing the capacitance changes the frequency of this pole, and you need to alter the compensation accordingly to maintain the required phase margin.

In current mode supplies, the output capacitor and load resistance create a single pole, and the output capacitor ESR creates a zero. Compensation on current mode supplies is a bit easier (barring weird things like slope compensation) but the sensitivity to output capacitance and output ESR is still there, so again, don't change your output caps too much.

Most computer SMPSes are voltage mode with a TL494 clone controller (or the odd SG3525 clone), but there's a few odd exceptions - I've seen current mode Antec SL's with a UC3844 controller. Most power supplies in television sets, printers, etc. tend to use UC384x's.

Lots of power supplies with bulging caps tend to whistle or hiss before they die. The failed/bulging capacitors in the output actually change characteristics to the point where they go unstable (while still providing enough regulation to keep the attached computer running, somehow) and you're actually hearing the transformer/inductors vibrate.

 

[thaltek]

Bought a broken 32" Westinghouse for $10. Replaced 4 broken backlights and a fried transformer, sold for $250. I repair tvs/monitors periodically for extra fun money. Got a few more to fix up before I can get a 5870.

from the Chicago area i see.....


oh where to start... well i used to have a tv that had to be rewired..... i was working on a vacuum tube amp and misplaced the ground connection and blew out the audio on the tv..... needless to say a vcr , receiver, and some rca cables and a little rewiring fixed it and provide kick ass surround sound with a 19" screen........

*has fond memories of watching stargate sg1 on that setup*

 

[BrainEater]

but anyways, hows the back of that PCB look? I'm horrible with a soldering iron, usually I can get it done but I'm still terrible at finessing that crap into where it needs to go.

Looks the same as before I started.....+1 on the desoldering braid.

---

I see CapXon. They made a bunch of bad capacitors (part of the taiwanese bad cap scandal, along with Fuhjyyu annd other makers) with an incomplete electrolyte that create hydrogen gas and bulge. And that's what you've got there.
-------

When you replace these capacitors, make sure you get ones with a equivalent or better ripple current rating, 105C temperature range and similar or higher voltage rating.

check,check and check.

I was not aware capXon was part of that.......good old fuhjyyu caps.....I've replaced those before...

 

[hotbrass]

I don't have pictures, but I once fixed a 30" tv with a gum wrapper.

We were at camp STEM (science, technology, engineering, and math) and were playing some Madden Football late one night when the tv went out. Being the geeks we were, we paused the game and busted it open to find a resistor had come loose. We didn't have any solder, so we peeled the metalic part from the paper backing on a piece of double mint (this makes the a little sticky piece of aluminum). We wrapped it around the resistor lead and stuck the other end into the board and "glued" it down to the trace. It worked like a charm.

We finished our Madden game and moved on to several hours of Super Smash Bro. Melee.

 

[n64man120]

from the Chicago area i see.....

Wait... did I miss something? That TV says San Francisco

 

[thaltek]

Wait... did I miss something? That TV says San Francisco

really cuz i saw san jose and oakland....