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You are right regarding the risk, but if you work with lots of surface mount component then you will have to mount them on the copper side. Audioguru - you saved my power supply. It is indeed the Q2 2n2219. I removed it and did a simple Base-Collector, Base-Emitter junction test on diode setting, it's open. I replaced with a new 2n2219, sorry that's what I got on hand, it's all good and working again. I will have to rebuild a new version someday when I have time.

Hello audioguru, Thank you for your time and reply. It helped me a lot understanding how those opamp works. I am into microcontrollers, never had much chance working with opamps. I learned to mount components on the non copper-side in highschool but then after many years of flipping, checking, flipping, soldering, checking I got tired of it, so I improvise. This is basically treating the through hole components as surface mount components. It has it's advantages and disadvantages. Firstly, there is risk of leads shorting to the copper tracks. Other than that I can't think of anything else which is bad. If you have enough experience of PCB prototyping I don't see why you can't do it properly. The advantages outweight the risk. By mounting the components directly on the copper side, you are looking at the interconnects. You can actually see all the circuitry including the tracks which has been cut to allow different electrical path together with the components. Flipping the board around increase confusion. When completed, to reduce risk of shorting, I spray a thick layer of varnish on the board as a conformal coating. This creates a electrical barrier between the exposed leads and copper tracks. My Q2 2n2219 and 3 other larger capacitors are mounted on the other side of the board. I will check Q2 later and see if it's the failing part. I will report back soon.

Hi guys, Sad day last week, I shorted my 6yr old power supply yesterday by connecting a 12v cordless drill pack battery to the psu without double checking the polarity. The power supply was set to 14.5v and current is limited to 14mA, I wanted to do cell balancing the battery pack by manual overcharging. And poof the psu died just like that. There's no sign of burn, I turn the voltage knob up but it would not go beyond 9volts. I checked the circuit, D11 1N4001 is blown, I replaced it. Everything else seems okay, I dont know how to check the TL081 op amps. I am using a 24v 3A 72VA transformer, I wonder how the TL081s survived for so long since you guys suggest changing to MC34071. Very sad for me since this power supply has been with me and helping me with my daily stuff almost everyday. I need to get it back up again. I am so surprise to find Audioguru still posting after so many many years! I have to find time to digest this 112 pages forum... Vincent. EDIT: After reading the last few pages of this post, I decided that my original 2004 circuit psu is not reliable, I will have to rebuild the psu with the updated schematics and parts.