Hello all . I'm hoping someone can shed some light on my problem . Ok , here we go .... I have built several surf pi 1.2 kits without a problem in the past . I then decided it would be interesting to source my own parts to build 3 more with boards supplied by silverdog as per usual . So every part has been checked , every ic and pot . After building the first , it was not operating . Upon checking , I noticed that some caps were box type but actually ceramic , so were replaced with poly film caps . This made no difference . I even moved all the ic's to a board that was functioning and it still continued to work. What I have noticed is the voltage offset pot ( again checked and working ) will not affect the voltage when adjusted ( it remains fixed at 1.1V with an input voltage of around 12V but it does vary on it's own when I input different voltages ie 9V to 13V . Nothing is getting hot and the circuit has live voltages at test points and most components. I have used other , presumably better quality parts on the other two boards with the same result ........nothing . The same voltage adjustment issue is present on these , so I have made the same mistake 3 TIMES ! . If anyone has any idea what parts would be affecting this function I will be absolutely delighted . Thanks and cheers , Dave .
Thanks for the reply Gary , hope you are well . voltage is .11V not 1.1 as I previously stated and there is no change in voltage when adjusted but the centre pin voltage is around 4V . The pot when measured across itself displays adjustable resistance but not through the circuit . Have you any idea which parts may have a bearing on the problem. I'm fairly sure it isn't an ic issue , I could be wrong so I will check the ne5534 again this morning. Cheers , Dave .
Hi Gary , I swapped out the ne5534 for the one in the working circuit . Voltage adjustment problem solved but it still doesn't work hahaha . I will have another look later on . Thanks for your time mate , if I had any hair left I would have pulled it out by now. Cheers , Dave .
Hello again , still pulling the last of my hair out. I know I am grasping at straws but is it at all possible that metal film and carbon resistors combined in the same circuit could affect it's operation as I have used both . Told you I was grasping at straws .........Cheers , Dave .
Dave, Before your pull out the last of your hairs :-) , would it be possible to post the pictures of both sides of your boards? Though the group would be limited to a visual evaluation (vice electrical), someone might be able to suggest a possible cause of the problem. At the very least, it would enable the forum to better grasp the problem at hand. Thanks!
Hi Radioman , I've already sent Gary a bunch of pics but they won't help much as the boards are double sided and lacquered black . I'm fairly certain it's not a trace problem as one of the boards I am troubleshooting actually works but the volume is extremely low with a huge emphasis on low . The volume control works to reduce and increase the volume to a just audible signal through headphones with their own volume control . Seems it's a parts problem , but eliminating them is time consuming . I have swapped out numerous parts with ,as yet, no success ......but I'm not giving up . I'm just becoming more determined ( another word for stubborn ).I'm thinking now , that a change of the mpsa 13 and the n3906 will be next using better quality parts . After that will be the rf 9604 and the 78lo5 . After that .....I will have a little cry and think of something else . Cheers , Dave .
Hi Dave, Your stubbornness is admirable - you don't give up easily! In my younger days, I had low volume with an LM386 based circuit that I had replicated many times in different projects but parts substitution failed to find any bad components (albeit there weren't as many in this circuit as yours). The culprit turned out to be in the cheaper headphones I was using - the impedance was in the realm of 300 ohms versus the 8 ohms of my other headset.
The reason I asked about posting of your pics was based on this website's purpose be a forum or discussion group. The website has been a good source of interest and learning to many, a number of whom may be silent, but nevertheless find the ideas here as food for thought. By just sending pictures to Gary limits the rest of us to the sidelines and wondering what all is going on - I don't think that was your intention.
Please forgive me for not uploading the pics as they are pretty much unviewable . I should have mentioned this fact , sorry everyone . I have been talking to Andy Beasley ( Silverdog ) about all kinds of possible causes and have possibly narrowed it down to either a bad batch (50) of LM358's or a smaller batch of 4066's . I have tried connecting speakers and different types of headphones and had the same results . Waiting on a new delivery of 4066 and 358 ic's and will go from there .I'm also going to get a complete kit as a control and a blank board for use with my own parts . So this is what I have found , ....there is a voltage change at pin 6 on the 5534 to ground when metal is passed by the coil. However, there is no voltage change on pin 7 to ground of the 358 which gets signals from pins 2 and 4 of the 4066 which are present in correct polarity .Some problem with amplification ? Possibly also the 4093 which will be replaced in turn . What really gets me is that all 3 turned out the same . At least I'm learning how these different components work and what they do together in a circuit .I would never have learned this much if I had not had this problem to solve .If you don't give up , eventually , you prevail !