Dragon's Lair Fans - Arcade Lifestyle
General Chat => Technical Area => Topic started by: Belike on May 03, 2012, 01:09:00 PM
-
I have a Tutankham pcb with a sound fault, I think it is the LA4460 sound amp broken, but I'm not sure.
I need some input how can I test the sound amp if it is working or not. :-*
Thanks in advance for any inputs.
-
Perhaps put a speaker to it ::) ;D ;D ;D ;D
Sorry for goofing around - to answer your question: i don´t know :-\
-
For about 5 bucks you will know if its broken or not ;D
http://www.twistywristarcade.com/sound-amps/37-la4460-sound-amp.html (http://www.twistywristarcade.com/sound-amps/37-la4460-sound-amp.html)
Just swap it dude ! :D
Now seriously, there must be a way to measure something on that thing, the question is how...
Maybe this pic helps a bit ?
If i get the pic, you should have the "12 volts DC" between pin 1 and 10.
Source: http://www.bucek.name/pdf/la4460,4461.pdf
-
Option 1:You can try putting a speaker against the input(of the amplifier chip) maybe hear a light sound
Option 2: take the input signal and use a cheap separate amplifier to see if you have sound
Option 3: use a scope to see if there is a signal you also can use a scope to follow the signal.
That are the things I found, have the same problem whit my outrunners pcb some problems in the sound circuits.
Only didn’t have the time to try them al out.
May be its useful
-
Thanks for the inputs guys, I will try out everything you advised. ;)
-
Here's a scientific one:
- straiten index finger
- move it around the pins of the amp (touching them)
- listen if you hear any changes....
Seriously I used this mehthod to find out that the LM324 on my Centipede was bust :)
-
Here's a scientific one:
- straiten index finger
- move it around the pins of the amp (touching them)
- listen if you hear any changes....
Seriously I used this mehthod to find out that the LM324 on my Centipede was bust :)
First question which one is the index finger? :D
Touching them means short it with a wire or touch it with the multimeter?
Ah, and does the board have to be powered up?
-
http://lmgtfy.com/?q=indexfinger (http://lmgtfy.com/?q=indexfinger) ;)
just touch the pins when its on, and there might be a buzzing noise (brom)
if you listen that, chances that you got a working amp are very high.
if you dont hear anything, you can almost assume its busted.
-
Lol, I thought index finger is a leg of the amp. ;D
-
LOL !!!
You can also use this finger:
(http://photos1.blogger.com/blogger/7386/358/400/realkid.jpg)
It will work just as well, but it just isn't very nice really is it (although it's great that Feyenoord did so well this year, so this pic is for all those who laughed at us a season ago :)
-
Made the finger test and there were absolutely no buzzing or anything else. :-\
Bought some of these amps then, fortunately just 2 eur/piece.
The sound pcb has a huge heat sink and the amp was under it.
Let's light up the soldering station :D
(https://lh3.googleusercontent.com/-a2AMzRnZt7E/T6Px11MQLvI/AAAAAAAAF5o/PiUQP7GQfE8/s640/WP_000158.jpg)
(https://lh4.googleusercontent.com/-ZDxQQLi5o9E/T6Px193tX3I/AAAAAAAAF5s/B4ftGP8Pm24/s640/WP_000159.jpg)
(https://lh6.googleusercontent.com/-a6l7JWzsyrs/T6Px22IPb0I/AAAAAAAAF58/mDU7OA667jI/s640/WP_000160.jpg)
New amp installed and some toothpaste applied. :D
(https://lh5.googleusercontent.com/-jHwPctGlKCk/T6Px3KBRebI/AAAAAAAAF6A/8w0e5W3hWIw/s640/WP_000161.jpg)
Let's hear the result
http://www.youtube.com/watch?v=D_hmvFi2ehw&feature=youtu.be
Thanks guys. ;D :spaceace: :spaceace: :spaceace:
-
Haha, the finger test never fails :P
Glad you fixed it. That is a bit much "toothpaste". Did you scrape away most of it ?
You really need to get a thin layer. I always scrape it away (using an old screwdriver) that you can see the part through the paste streaks...when you press the part to the heatsink (or screw it again), it will produce a nice thin film...
-
Thanks for the tip André, my layer is a bit thick indeed, it was my first try with this method. :D
-
wonderful, bela, you're getting better by the minute!
eh, can someone school me on the "toothpaste", please?
-
Normally, there is a layer of a special gel or paste between the heat sink and the processor or amplifier, afaik the components can melt together without this from the extreme high temperature.
(http://i.ebayimg.com/00/s/NDAwWDQwMA==/$(KGrHqJ,!pIE9c6i5w5uBPgBNPlt-w~~60_1.JPG)
-
No they don't melt together, its to conduct the heat better to the heatsink, it "fills" the imperfections between the chip and the heatsink
So its to improve the cooling
-
Yep. Use the cheap regular type thermal grease. DO NOT EVER EVER use Arctic Silver or similar stuff on transistors on old "arcade" hardware because that is not only thermally conductive but also electrically and usually you do NOT want that....
Besides, it is WAY overpriced because of the "coolness" factor it has in the PC modders scene.... it only has slightly better performance than the "old fashioned" grease but costs insanely more.
I can't find a drawing that explained how thermal grease works that I learned while at electronics school anywhere on the internet....it's so simple but totally explains why it is needed.....if I have some extra time I'll make and post it.
Don't smear the stuff with your bare hands. I seem to remember BITD they said it was toxic, but I doubt it if it (still) is...there are no warnings or whatever on the packaging....but the reason not to smear it with your hands is because you will introduce dirt/grease/acid particles into it which will not help in the thermal conduction.
-
and dont forget that its a real PITA to wash it off your hands / fingers ;D
-
and dont forget that its a real PITA to wash it off your hands / fingers ;D
Nope, use PURE alcohol (get it from the "drugstore" or drogist as we call it....) and a paper towel. I use that to remove excess grease on the heatsink too...
Judging from last Eurocade some Hungarian liquors may work well too......... ;D ;D ;D ;D
-
Judging from last Eurocade some Hungarian liquors may work well too......... ;D ;D ;D ;D
I don't know, ask Robin. ;D ;D ;D
-
Hahaha, that was a funny read! - glad you got it working! - you´re improvement i rising, fixing these things! Are you on level 8 now? ;D Dre must be on level 42 or something ;D ;D ;D
-
Nahhh....Speleo and RobinHolland are much better than I am. Fixing vector monitors is easy. They are really pretty simple devices. Much simpler than raster monitors or game PCBs...
-
Nahhh....Speleo and RobinHolland are much better than I am. Fixing vector monitors is easy. They are really pretty simple devices. Much simpler than raster monitors or game PCBs...
Perhaps they are Level 60+ then?? ;) ;D ;D
Everything is easy when you know how to do it....
-
Here one of my famous drawings:
(http://gallery.me.com/andre.huijts/100937/IMG_0222/web.jpg?ver=13362979150001)
Imagine this is a microscopic picture of the surface of the transistor (upside) and heatsink (down). The surfaces are NOT flat on a microscopic level but actually very rough. And THAT is the main role of the grease. If you don't use the grease, the contact between transistor and heatsink will be very minimal. THUS you have a terrible conduction of the heat from the transistor into the heatsink. The grease fills up the gaps and is of a material that conducts the heat easily into the heatsink.
If you have a mica plate between the transistor and heatsink, it just adds a layer in between, so grease must be applied on both sides. Mica is a kind of STONE (!) even though it's transparent. It will break like a stone if you bend it too far. So, you can imagine it will have a rough surface too.
Now, if you have air bubbles or dirt elements in the grease you can also imagine it will hinder the transfer of heat into the heatsink.
Anyway, I hope this awful picture makes it clear :)
After 30 years it is a good idea the replace the mica and thermal grease on critical transistors like deflection transistors on vector monitors. The mica and grease dry out over time and loose their heat conduction.
I have experimented with it on my Amplifone board. The transistors felt a LOT cooler after I had redone the mica's and grease. If you can feel a temp difference with your fingers, it's a pretty big difference because they are not THAT sensitive that you can feel a difference of a couple of degrees.
I would love to have a heat-camera or even temperature probe to do a one-on-one compare "before" and "after".
-
Here one of my famous drawings:
(http://gallery.me.com/andre.huijts/100937/IMG_0222/web.jpg?ver=13362979150001)
Anyway, I hope this awful picture makes it clear :)
I love the pic ;D its very clear and the dirty piece really looks dirty ;) :D
maybe you would like to have my Wacom ?
I hardly use it, and i got 2 of them..
(http://f.rimg.com.tw/s2/e/ce/ca/21201057935050_580_m.jpg) (http://4.bp.blogspot.com/_-RKOyn2PyCA/S42NolEGdoI/AAAAAAAAA0A/GB_HTPGgimw/s320/DSC00570.JPG)
-
Nice pic & explanation, I love to learn and understand things like this. ;)
-
Hey it was an iPad drawing done in 10 seconds :)
But If you have one Wacom extra.....that would be very cool :) I know they work on Macs too :):)
You're welcom Béla...surpringly I didn't find a similar drawing like this anywhere but thus is how it works. Maube the transistor and heatsink are a bit closer together but you get the idea, the greas "fils the gaps" where else air woulda be. That it can be destructive is proven by Franck's WG6100, I'm quite sure the transistor blew because of the lack of thermal grease...