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Post by praetor on Jul 21, 2009 8:00:39 GMT
Hi all, I've been reading this forum for quite a while now, and after reading about the Jaycar amp on here I decide to give it a go and build one. Got all my parts, box, transformers and all, and went ahead and started building it. By about 3 am in the morning, and 2 sliced and toasted fingers later(I bought a wire stripper and a soldering iron stand the day afterwards), the whole board came together, or so I thought. After powering it up briefly (Checked the PSU output is +/-15v), I noticed that LED1 is not lighting up. Double checking the circuit made me notice that I got all the transistors the wrong way around After I swapped the transistor back the right way, I discovered that my LED1 is blown. LED of the exact spec is not available in JayCar. Are there any good alternatives to the original z0700 LEDs? Thanks in Advance
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Post by Deleted on Jul 21, 2009 8:50:15 GMT
praetor I have found that the Cat.no. ZD0120 3mm green diffused LEDs from Jaycar, have a forward voltage of approx. 1.85V at 1mA, and are a suitable replacement for the RED LEDs supplied in the kits. Why not replace the whole lot with the green ones, as they are only about 20C each. Perhaps buy 8 in case of further mishaps ? These are used in Miguel's SC HA,just to be different. Alex
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Post by praetor on Jul 21, 2009 10:49:54 GMT
Hi Sandyk,
Thx for the quick reply! Judging from the way I put together the circuit, buying 8 is probably a good idea! I just hope I have not damaged the transistors. On a side note, I noticed that on my Jaycar PSU, the 5 w 300 ohm resistor is extremely hot, in that it can burn you in the space of a second, while the other big white one is cool to touch(possibly because I haven't put any load on the supply yet.
Hopefully the LED will be the only broken component. Will keep you guys posted!
Tom
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Post by Deleted on Jul 21, 2009 11:15:26 GMT
Tom Have a look at the modified PSU shown in the "Tweaks" thread. The HA will perform a little better without that hot 330 ohm 5W resistor, which is not needed in this application. You can even leave out the 7805 regulator and associated components. If you also replace the 100 ohm 5W resistor with a 10Kohm metal film resistor, you can then use the 2 pin 5V output terminals to directly supply either a Blue or Purple (UV) front panel LED. Alex rockgrotto.proboards.com/index.cgi?board=chitchat&action=display&thread=3622&page=1
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Post by Deleted on Jul 22, 2009 0:48:47 GMT
Now I understand why my led's are green and not red! Miguel No,I did not blow anything up and need replacement LEDs ! It was a delierate decision to give you something a little more unique. Alex P.S. Anybody fancying something slightly different, could fit the 3mm Yellow diffused LEDs from Jaycar. Cat. no. ZD0110 @ 20C each.
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Post by praetor on Jul 22, 2009 15:28:10 GMT
sigh, turns out it isn't the leds.... Guess I will have to slowly check through the circuit...
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Post by Deleted on Jul 22, 2009 21:49:53 GMT
Tom After you locate the problem, whether it is a solder bridge, component in the wrong place, or orientation,or whatever, it may be worthwhile replacing all the transistors to be on the safe side, but mainly to save heaps of time.Try replacing the BD139 and BD140 initially. It will only set you back about $5.05. Alex
Miguel As if I didn't know ! ;D Alex
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