Hi All,
I need some help. I've been trying to develop my electronic skills and knowledge, so as a project bought an old Pioneer graphic eq.
I took it all apart and started resoldering all the joints... mainly just for practice. When resoldering resistors I clipped a crocodile clip to the wire as a heatsink... if I could get a crocodile clip on the I didn't bother resoldering.
I then replaced all the electrolytic capacitors. But some of the smaller values I couldn't get so the smallest was replaced with one with slighter higher uF value, another was replaced with polyester film capacitors, one box style and one of a similar appearance to ceramics. I think polyester caps are non polarized so obviously I didn't worry about which way to put them in.
All the caps that aren't quite right are on the eq part of the circuit and the ones of correct value at the power supply end.
However, something has gone wrong. you can just about here sound, but it is incredibly quiet and very distorted.. also the power on led doesn't power up now although it 1.2v
Can anybody help suggest what the problem is... is it the caps (the man in the shop said they'd be fine) or am I more likely to have burnt stuff out soldering?
I need some help. I've been trying to develop my electronic skills and knowledge, so as a project bought an old Pioneer graphic eq.
I took it all apart and started resoldering all the joints... mainly just for practice. When resoldering resistors I clipped a crocodile clip to the wire as a heatsink... if I could get a crocodile clip on the I didn't bother resoldering.
I then replaced all the electrolytic capacitors. But some of the smaller values I couldn't get so the smallest was replaced with one with slighter higher uF value, another was replaced with polyester film capacitors, one box style and one of a similar appearance to ceramics. I think polyester caps are non polarized so obviously I didn't worry about which way to put them in.
All the caps that aren't quite right are on the eq part of the circuit and the ones of correct value at the power supply end.
However, something has gone wrong. you can just about here sound, but it is incredibly quiet and very distorted.. also the power on led doesn't power up now although it 1.2v
Can anybody help suggest what the problem is... is it the caps (the man in the shop said they'd be fine) or am I more likely to have burnt stuff out soldering?
You probably didn't burn anything up ffrom heat. But in soldering and desoldering a bunch of stuff, you may b=very well have failed to make a connection or you may have caused a solder bridge - a place where a blop of solder touches two things together that should be separate. Also, in the assembly and disassembly, in many units it is possible to get a connector on the pins one pin off, or two same-size connectors can wind up on one another's spot.
I would be checking that all power supply voltages were present. And to help much further, we might want to see a schematic. If you have one, maybe post it or provide a link to it. Or provide the model number so we might find one.
I would be checking that all power supply voltages were present. And to help much further, we might want to see a schematic. If you have one, maybe post it or provide a link to it. Or provide the model number so we might find one.
I haven't been able to find a schematic, and pioneer couldn't supply one. but the model is SG-550.
I'll have a check over the board but I'm confident there are no bridged connections. It's old kit, with big parts all well spaced out, nothing fiddly.
I'll have another look. The problem seems to be before the EQ circuit as the EQ slides don't affect the small amount of sound coming out...
and I've just noticed that the led's on the right channel slider are faintly pulsing with the music. something must be touching something it shouldn't be.
I'll have a check over the board but I'm confident there are no bridged connections. It's old kit, with big parts all well spaced out, nothing fiddly.
I'll have another look. The problem seems to be before the EQ circuit as the EQ slides don't affect the small amount of sound coming out...
and I've just noticed that the led's on the right channel slider are faintly pulsing with the music. something must be touching something it shouldn't be.
sometimes when re-soldering oooold equipment, what happens is the solder sits 'over' the component leg or circuit trace, so what was soldered, now isnt.
best way to learn the finer points of soldering is to invest in a decent size illuminated magnifier, that way you can see if you really have soldered the joint, or just 'flashed over' a dirty one.
might have to desolder, clean/flux, the resolder the joints.
the pulsing of the led to me suggests failed or poor solder joints leading to power supply problems..
EDIT, age creates oxides (rust) on their legs, makes it a biatch to solder cleanly and reliably.......
best way to learn the finer points of soldering is to invest in a decent size illuminated magnifier, that way you can see if you really have soldered the joint, or just 'flashed over' a dirty one.
might have to desolder, clean/flux, the resolder the joints.
the pulsing of the led to me suggests failed or poor solder joints leading to power supply problems..
EDIT, age creates oxides (rust) on their legs, makes it a biatch to solder cleanly and reliably.......
when I did it, I de-soldered everything before adding new solder. As I can't see any bridges, I'm going round the board with a multimeter checking for continuity between solder point connected by tracks on the board.... I have found some thing a bit odd. there is one track with about 5 solder points spread along it, between the first 2 solder joints I have continuity and between the last 3 I do as well but no continuity between the either of the first 2 and the last 3... could the track of somehow become separated? can I use a bit of wire to just bridge across all the joints?
sometimes desoldering and resoldering isnt enough.
sometimes a little flux or gentle scraping of the joint is needed.
'tracks' can indeed break (crack).
the type and construction of the board may also lead to problems.
some boards have the tracks and via's (pads around component legs) as separate parts, and can become separated from each other.
with it turned on, at low volume, try gently pushing on different areas of the board with something like the handle of a plastic tooth brush.
this will flex the board and help show up any bad joints and broken tracks.
And yes, if theres a break in a track, a few strands of wire is certainly doable.
many things have i repaired with a bit of wire where tracks have been burnt or blown clean of the board..
sometimes a little flux or gentle scraping of the joint is needed.
'tracks' can indeed break (crack).
the type and construction of the board may also lead to problems.
some boards have the tracks and via's (pads around component legs) as separate parts, and can become separated from each other.
with it turned on, at low volume, try gently pushing on different areas of the board with something like the handle of a plastic tooth brush.
this will flex the board and help show up any bad joints and broken tracks.
And yes, if theres a break in a track, a few strands of wire is certainly doable.
many things have i repaired with a bit of wire where tracks have been burnt or blown clean of the board..
ok bridging that joint did it. Thankyou for your help. I was so disappointed when it didn't work. But I still can't figure out why the power led doesn't work anymore.
your welcome 😀
led, possibly another bad joint or broken track.
try the 'gentle push on the board' trick.
could also be the led itself has failed. yes, they do indeed fail.
led, possibly another bad joint or broken track.
try the 'gentle push on the board' trick.
could also be the led itself has failed. yes, they do indeed fail.
The power LED is fed from the -11.5v rail through R79 (560R). I would not be surprised to find the LED faulty. Hang another one in series to check there is enough current to light it up.
Well done to get this far!
Well done to get this far!
I tried attatching another with led in parallel but no luck. The led is fine, but I tried a new one just in case. I've also reversed it incase i'd put it in the wrong way round.
There was only 1.2 volts going to the led... nowhere near 11.5v, I tried swapping out the 560r resistor for about 320ish but still no good.
There was only 1.2 volts going to the led... nowhere near 11.5v, I tried swapping out the 560r resistor for about 320ish but still no good.
- Status
- Not open for further replies.