freezy Posted February 21, 2013 Share Posted February 21, 2013 Hi folks, before completely hijacking the other thread, I thought I'd post the follow-up in a separate one. Many thanks already to maxx and zebulon who helped me out a lot! For the history, my main power switch seemed to have produced an over current which blew out the fuse of my amp: Since I didn't have such small fuses and I certainly didn't feel like soldering a new fuse every time it blows, I've soldered two wires to an external fuse holder and screwed it into the amp: The fuse that was blown says T1AL250V which I suppose stands for 1A slow blowing at 250V. So I've ordered some of those, but when I plug the amp, it blows instantly. Now zebulon mentioned that the resistors may be damaged as well. I tried to take a better photo: Could that be the reason the fuse blows? And if so, can anyone decrypt which kind of resistor those are so I can replace them? Thanks in advance, guys. Link to comment Share on other sites More sharing options...
russdx Posted February 21, 2013 Share Posted February 21, 2013 the colour bands tell you what value you it is then just need to find a similar sized one Link to comment Share on other sites More sharing options...
maxxsinner Posted February 21, 2013 Share Posted February 21, 2013 As you can probably tell freezy, that resistor has been cooked! Looks like a 100 ohm resistor if I am right with the colors of brown, black, brown. Might be something further upstream that caused the resistor to blow. Cheap fix if it is just the resistor and fuse.... What do you reckon Zeb?? Do you think that might be the resistor for the transistor shown in the first shot?? The gate might be cooked? (thinking outloud here) Link to comment Share on other sites More sharing options...
freezy Posted February 21, 2013 Author Share Posted February 21, 2013 Thanks for the feedback, guys. Firstly I was confused by the silver ring, but when looking closely that's the resistor behind the plastic layer, which was originally indeed brown / black / brown / gold, which stands indeed for 100ohm. The gold ring means +-5% tolerance, right? I found this, however it says only 1% tolerance. Is that a problem? Link to comment Share on other sites More sharing options...
zebulon Posted February 21, 2013 Share Posted February 21, 2013 Yup, swap out that resistor and the other one (R30, probably a similar value). As well, replace Q1 (the transistor). It's going to be something along the lines of a 2n3906 or 2n3904 (depending on how they ran the circuit, tough to see). I'd also look for a diode somewhere that has blown. If all that fails, I'd bet the transformer is cooked. Gold bands are 5%, silver are 10% (I believe, would have to double check). I wouldn't worry about the tolerances for now. Get it working first and then fine tune if necessary. Link to comment Share on other sites More sharing options...
freezy Posted February 21, 2013 Author Share Posted February 21, 2013 Thanks, Zeb! The other resistor also looks like 100 Ohms: So the tolerance doesn't affect the functionality? Do you need an image from a different angle in order to determine which transistor is used? Also I have no idea how to solder the transistor, this one looks quite different than the one on the board. Link to comment Share on other sites More sharing options...
freezy Posted February 21, 2013 Author Share Posted February 21, 2013 About the diode, this one is the only one I could find and it looks quite okay, right? Link to comment Share on other sites More sharing options...
russdx Posted February 21, 2013 Share Posted February 21, 2013 tolerance does effect functionality! but getting a smaller tolerance resistor then your current one is ok high tolerance ones like 0.5% and 1% r normally used in adc's and other high accuracy systems low tolerance are normally used for pull up/down resistors or for leds or somin, basically where you really dont care if its exactly the value its ment to be. Link to comment Share on other sites More sharing options...
freezy Posted February 21, 2013 Author Share Posted February 21, 2013 Thanks, russ! So should I try replacing the resistors already or do you guys think that the transistor that is between is definitely cooked too? Link to comment Share on other sites More sharing options...
freezy Posted February 21, 2013 Author Share Posted February 21, 2013 By the way, are you guys sure the C7 in the middle is a transistor? Don't those come with three terminals? I have only two there: On the back, it looks like this: Link to comment Share on other sites More sharing options...
russdx Posted February 21, 2013 Share Posted February 21, 2013 C7 is a capacitor R=resistor (2pins) C=cap (2pins) Q=transistor (3pins) Link to comment Share on other sites More sharing options...
freezy Posted February 21, 2013 Author Share Posted February 21, 2013 Oh right, I overread zebulon's remark about Q1. Are transistors usually labeled? Should I scratch off the yellow stuff that is glued on top and see if I can get more info about which transistor it is exactly? Link to comment Share on other sites More sharing options...
maxxsinner Posted February 21, 2013 Share Posted February 21, 2013 Yeah scratch it off freezy to see what the code is. Link to comment Share on other sites More sharing options...
zebulon Posted February 22, 2013 Share Posted February 22, 2013 May find those smd transistors are gone too... Link to comment Share on other sites More sharing options...
freezy Posted February 22, 2013 Author Share Posted February 22, 2013 May find those smd transistors are gone too... Then I'm kind of screwed, right? Link to comment Share on other sites More sharing options...
freezy Posted February 22, 2013 Author Share Posted February 22, 2013 Scratched off the yellow stuff. Not sure if I can get a better picture, its not readable at all by bare eye... Does that speak to anybody? Link to comment Share on other sites More sharing options...
zebulon Posted February 22, 2013 Share Posted February 22, 2013 LMAO...you know, I just realized what we're going through all of this for. Freezy, do you know what the voltage output of this power supply was? You could most likely just replace it with a wall wart and be back up and running. It's most likely that it was in the 12v-18v range. Link to comment Share on other sites More sharing options...
freezy Posted February 22, 2013 Author Share Posted February 22, 2013 Yeah that's what I thought too at the beginning, but the PCB where the PSU seems to be is the same where all the inputs and outputs are soldered onto. Then a bus goes up to the other board where the amp and whatever is. Not sure how I would just replace the power unit... Link to comment Share on other sites More sharing options...
zebulon Posted February 22, 2013 Share Posted February 22, 2013 Offhand I'd say that the red and black wires coming off the board are your power feeds for the amp. If you ran a ground to the black and left it connected to the circuit board and disconnected the red from the board and connected it to a power supply you would be bypassing the onboard power supply. If you could get the amp powered up that way, I'd just remove the transformer and burnt components from the board to eliminate any possible interference/feedback of voltage and connect the power supply to those wires and plug the red back into the board. Basically, you strip the old supply hardware out of the board and connect at the output terminals of the old amp. As long as everything else is removed, there's nothing left to short to. Link to comment Share on other sites More sharing options...
freezy Posted February 22, 2013 Author Share Posted February 22, 2013 To be honest I don't feel too confident about this solution. Normally if pros like you guys start guessing I'm already completely lost. Additionally I don't have any of those components lying around, so every time something burns I need to order it somewhere with shipping costs and delays involved. So my current plan is to find the right transistor, replace the two resistors and the transistor, and if that doesn't work throw the whole crap out of the window and buy a new one. Therefore, suggestions about which transistor to find would be very appreciated Link to comment Share on other sites More sharing options...
zebulon Posted February 22, 2013 Share Posted February 22, 2013 Looks like a "something 002T" in the pic, can't seem to find anything on google.... Link to comment Share on other sites More sharing options...
freezy Posted March 1, 2013 Author Share Posted March 1, 2013 Resistors finally arrived. However they look completely symmetrical. Is the orientation important at all when soldering into the PCB? Link to comment Share on other sites More sharing options...
freezy Posted March 1, 2013 Author Share Posted March 1, 2013 Seems not. However, the fuse still blows as soon as I plug the amp. Any idea why? Could it be my amateur soldering of the fuse? Or could a broken transistor be the cause of that? EDIT: This is how it looks now: Link to comment Share on other sites More sharing options...
freezy Posted March 1, 2013 Author Share Posted March 1, 2013 Hmm I've just noticed that my replacement fuse (left) says T1L250V while the original (right) reads T1AL250V. Maybe that's the problem? Doesn't the "A" just stand for ampere? Link to comment Share on other sites More sharing options...
zebulon Posted March 1, 2013 Share Posted March 1, 2013 Well, the original fuse was a slow blow fuse, as long as the replacement is a 1A fuse there really is no difference based on the surge that the burning shows is happening. That transistor is definitely gone but I'd be willing to bet the problem goes much deeper than that. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.