Ok, i just soldered everything onto the board and went on to the step where i check the voltages. 0V practically everywhere except directly at J1, where i get the 9V dc from my psu. trying to find out whats wrong myself i also found a voltage of 0.5V between pins 1 and 2 of the 7805, and a resistance of 1.5MegaOhm or just a few depending on polarity between two of the pins of the rectifier and infinite resistance between all other pins of the rectifier, regardless of polarity. what’s wrong? did i fry the rectifier during soldering, or the 7805, or is it something completely different?
edit: just in case it matters, it’s one of the old core boards, with the quartz on the bottom
The voltage at J1 is where the power supply is connected. In your case you measured 9V. This is ok. You mentioned you got only 0.5v a between pin 1 and pin 2 of the 7805. This seems to me that you may have wired the rectifier X1 incorrectly. Are you using 4 diodes or just unit with 4 leads. Make sure you follow the schematic and wire the diodes correctly. Disconnect pin 1 of the 7805 and with no power applied to J1, use an ohm meter to measure the positive (+) and the negative (-) line, (positive lead of meter red colour) to the (+) side, you should get some reading in k ohms and almost infinity if the leads were reversed.
i used a unit with four leads, and it is on the board just as it is supposed to according to the schematic. how am i supposed to disconnect pin 1 without removing the 7805 completely? ???
On the rectifier unit (with 4 leads) two of them are marked (+) and (-) and the other two are not mark or marked as AC. Before you remove the 7805, use your ohm meter to measure the terminals on J2, there should not be a short circuit (zero ohm). I also attached a a drawing to help you troubleshoot. If all things failed, then remove the 7805 and do the measurement again. Hope this will help.
well, as i mentioned it is mounted exactly as it is supposed to with the + the - and the two ~ leads at the same place as shown in the schematic. between the + and the - (with 7805 mounted) there is a resistance of infinity, regardless of polarity, as mentioned in the first post, and where the voltage is marked 9v behind on your drawing is where i measured 0.5V (between 1 and 2 of the 7805) and where there should be 5v i measured 0. between the pins of J1 i measured an infinite resistance (or at least larger than 2MegaOhms, which is the highest my multimeter can measure) and between the two pins of J2 a resistance of 10.5kOhm.
EDIT: I re-measured the + and - of the rectifier and although it displays infinity, when i switch polarities it displays a non-infinite resistance for a short moment, but i’m pretty sure i just charged the caps with my multimeter
I hope you have some luck with the power supply. I attached there snapshot of the core layout and a cheap device that I use to desolder by sucking out the molten solder.
ok i managed to desolder the 7805, or rather to desolder it a bit as the wick practically didn’t seem to remove anything and tear it out. if it wasn’t broken before i’m pretty sure it is now, considering how hot it became during the process and how hard i had to pull on that thing… >:(
now, i conntected the psu, and checked the voltage between the + and the - pins of the rectifier. it seemed to fluctuate between 1 and 2 volts (the fluctuating may be the multimeter though as it’s on of those sucky cheap ones) so yeah, i guess the retifier is fubar. (and probably the 7805 as well, and if not i don’t know how i would manage to get it back in…)
and with my luck i probably fried the single diode and the transistor as well
You conntected the psu, and checked the voltage between the + and the - pins of the rectifier and the voltage fluctuates between 1 and 2 volts, it would seem that the rectifier is either connected incorrectly or the rectifier is no good. Try us the AC scale of the multi-meter to measure the + and the - pins of the rectifier again. If you got a higher voltage, then it is connected the wrong way round. Try buy one of the sucking devices shown in the picture in my pervious posting, it will help very much to desolder component from circuit board. Radio shack sells them.
the only way the rectifier could be connected wrong is if the writing on the rectifier is wrong, and as i mentioned, i think the fluctuating is the multimeter (it also fluctuates between 8.5 and 9.5 volts when directly at J1, and also fluctuates when i check a resistor by itself, as i said: its a piece of junk)
well i have another one of those rectifiers lying around (for the SID board, but there’s no point in starting to build that before i get the core in working order) so i might just try to replace the current one this evening and hope not to break that one as well…
Good luck.. I still think a desoldering tool is a good investment. It is easy to pull out components with it without over heating the traces that can damage the PCB.
Perhps a little tip to clear the hole of solder on the soldering pad. Melt the solder on the pad quickly at the same time use a fine tooth pick to poke through the melted solder leaving a clear through hole.
Good luck.. I still think a desoldering tool is a good investment. It is easy to pull out components with it without over heating the traces that can damage the PCB.
i just removed the rectifier put in the one i had lying around and it conducts just fine between + and -… regardless of polarity. and i double, and triple checked for any solder going across two lanes… nothing.
i think this is my first and last real diy electronics project. i guess i should stick with soldering my own audio cables.
i just removed the rectifier put in the one i had lying around and it conducts just fine between + and -… regardless of polarity. and i double, and triple checked for any solder going across two lanes… nothing.
Keep in mind you are testing it in circuit, meaning your meter is showing you the continuity of everything connected to the bridge rec, not just that one part…ceramic caps usually show as shorted or very low resistance, etc. so the path you are seeing on the meter is probably not the bridge rec.
i think this is my first and last real diy electronics project. i guess i should stick with soldering my own audio cables.
You give up too easily…this statement says you are not willing to learn, and I doubt that is true else you would not be here.
I am still learning (and forgetting!) all the time after all the years.
