I just acquired an ancient Vestax PMC09 DJ mixer, non-working - problem easily traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed. This defunct LM7815 TO-220 IC (15 v o/p) is an old repair and likely isn't the right one as its data sheet specifies a minimum input volts of 17.9 but the mixer's external psu socket says only 15v. Other specs recommend that a 15v psu should be good for an LM7812, 14.8-27 volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output. Not being able to source service sheets to check, is a 12v regulator the most likely ? 5v o/p seems a big drop from 15v input and so less likely; they would have used a smaller psu voltage in that case.
And what does the external PSU actually produce on/off load?
Why do you suspect that the "old repair" has used a 15 V regulator if the orginal was 12 or 5. The chances of the downstream electronics objecting to 15 V is reasonably high, especially if it's expecting for 5 V!
Any clues on the PCBs of supply rail voltages, personally I'd stick with the LM7815.
traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
right one as its data sheet specifies a minimum input volts of 17.9 but the mixer's external psu socket says only 15v.
volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
likely ? 5v o/p seems a big drop from 15v input and so less likely; they would have used a smaller psu voltage in that case.
5v would also be a bit low to run audio circuits. 12v would seem to be a good choice and 3v input to output headroom is good enough.
9v and 8v versions exist. Maybe check the application circuits for any ICs in the device for their recommended operating voltage range and stay away from the maximum.
You might want to consider why the regulator has failed in the past. They are shortcircuit proof and have thermal shutdown. They are pretty hardy with their only real vulnerability is a higher voltage on the output compared to the output which can occur momentarily during switch off. A 1 amp diode (1N4000 series) from input to output (cathode to input) make these regulators virtually indestructible at minimal cost.
You could try an LM317T - which is an adjustable three terminal regulator. It is easy to use and robust. Info from
formatting link
and elsewhere.
If you are not sure what internal voltage the mixer originally ran, on you can set the regulator to (say) 6v initially, and see how the mixer behaves. It will probably work, but will overload easily. If this is the case increase the voltage in steps until the results are satisfactory.
317's can take up to 35v input, and need a minimum of about 3v between input/output to function correctly. It is a good idea to measure the external PSU voltage to determine what differential you have to play with. You can make up the simple control circuit for the regulator on veroboard, and a multiturn preset pot is a good idea for the voltage adjustment. The regulator needs heatinking of course - size dependent on dissipation.
traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
right one as its data sheet specifies a minimum input volts of 17.9 but the mixer's external psu socket says only 15v.
If it is an old unit with a traditional unregulated external PSU then chances are the input voltage is around 18v anyway.
volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
likely ? 5v o/p seems a big drop from 15v input and so less likely; they would have used a smaller psu voltage in that case.
It is providing one of the supply rails for opamps. Probably should be a
7815 or 7812 and would not make a lot of difference which one you use.
The key question to ask yourself is why has this component previously failed (aka old repair)? Inadequate heatsinking to overload it but they should fail gracefully and go into safe thermal foldback shutdown.
It takes real skill/gross incompetence to design a circuit to kill them.
The only thing I have known kill them is very bad heat sinking coupled with inadequate supply decoupling leading to wild RF oscillations. ISTR It also required provoking them with very fast switching transient load.
The 0.1uF capacitors close to the device are essential!
Often you can get an idea of the supply voltage from the capacitors. In fact one of the things that blows regulators are thus little bag or resin electrolytics that for no good reason go short circuit on their own. If the mixer does in fact work when powered from another supply then you are probably OK, but I've come across a lot of thes in my past that just go, even though they are rated for far more volts than the rail supply. Bloody pain in the rear, which thankfully not being able to see has meant its somone elses problem!
what they are NOT protected against is overheating - they SHOULD be, but they are not (always) so especially older examples.
Some demonstrably are, as I discovered when my model tiger moth shut its motor down and spiralled into the ground.The 7805 had shut down (to about 1v) in protest from overheating, and the servos all went hard over.
asily traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
t the right one as its data sheet specifies a minimum input volts of 17.9 b ut the mixer's external psu socket says only 15v.
7 volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
most likely ? 5v o/p seems a big drop from 15v input and so less likely; t hey would have used a smaller psu voltage in that case.
78 series need a 4 or 5v drop or more to work, so a 15v reg on a 15v input makes no sense. If the socket's marked 15v, and a 78 type reg used, it woul d need to be 9v or less, ie a 7809. I cant see a 7805 being correct, droppi ng 15v to 5v makes no sense. So it sounds like its designed to run on 9v... Unless it was deisgned with no internal reg, and used a regulated 15v psu. Really you'd best look more at the circuit to determine what you need. But it sure isn't going to be a 15v psu and a 7815 reg!
easily traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
the right one as its data sheet specifies a minimum input volts of 17.9 but the mixer's external psu socket says only 15v.
volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
likely ? 5v o/p seems a big drop from 15v input and so less likely; they would have used a smaller psu voltage in that case.
makes no sense.
Rubbish they need at most 3v headroom to work. The larger the voltage dropped across the linear regulator the more heat it has to dump.
less, ie a 7809. I cant see a 7805 being correct, dropping 15v to 5v makes no sense. So it sounds like its designed to run on 9v... Unless it was deisgned with no internal reg, and used a regulated 15v psu. Really you'd best look more at the circuit to determine what you need. But it sure isn't going to be a 15v psu and a 7815 reg!
It sounds like a prehistoric old iron core transformer unregulated "15v" supply at maximum current draw which translates to 18+ volts most of the time. In the days before switching regulators PSUs were heavy, crude and nasty. Big lump of iron some copper a bridge rectifier and a capacitor.
These days wallwarts are light weight cheap and nasty. Unclear whether or not the OP might be better off using a modern external regulated PSU and bridging out the on board regulator entirely.
I ran a few tests using a 7805 and found that I couldn't get them above 270 ma without them overheating abd the 5V o/p falling as the current and more importanly the case temperature rising. The Maximium temp I got to was abou t 120C before the the o/p started to drop and noise levels increased. Removing the genetrated heat by adding a heatsink to reduce the temperature made it possible to increase the current while maintaining 5V o/p . producers.
m easily traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
sn't the right one as its data sheet specifies a minimum input volts of 17.
9 but the mixer's external psu socket says only 15v.
8-27 volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
he most likely ? 5v o/p seems a big drop from 15v input and so less likely ; they would have used a smaller psu voltage in that case.
put makes no sense.
Most seem to be 17.5V for minium i/p voltage, some called LDO can be a litt le as 15.5V but they tend to be surface mount devices, 7805 LDO i.e 5.5V mi n i/p are more easily found and quote common as are the 3.3V LDOs . The LDO appear to have a lower maxium i/p voltage too arounbd 23V rather th an 30V.
9v or less, ie a 7809. I cant see a 7805 being correct, dropping 15v to 5v makes no sense. So it sounds like its designed to run on 9v... Unless it w as deisgned with no internal reg, and used a regulated 15v psu. Really you' d best look more at the circuit to determine what you need. But it sure isn 't going to be a 15v psu and a 7815 reg!
asily traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
t the right one as its data sheet specifies a minimum input volts of 17.9 b ut the mixer's external psu socket says only 15v.
7 volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
most likely ? 5v o/p seems a big drop from 15v input and so less likely; t hey would have used a smaller psu voltage in that case.
Many thanks for all the ideas. Am on Google groups so can't really split u p replies. I don't have the original PSU which would have been a a traditi onal heavy iron type in the day but electrically quieter than switched mode . I guess the regulator is a cheap way to cut out the 100 Hz mains ripple. The headphone o/p works fine, but the main output has a lot of hum.
I already put 12v from an uregulated variable wall wart psu on the reg. o/p side so if anything's going to fry it maybe already has. It's probably dra wing less than 100mA so have no idea why the (heatsinkless) 7815 has blown, nor is it clear what the logic of repairing it with a 7815 was anyway. A
9v regulator option could well be the original, and the guy who repaired it couldn't find one so he stuck a 15v one in. Probably not a professional j ob then. If I can get the rest of the upside-down boards out easily I'll look for vo ltage clues like 5v IC's and go for 5v or 9v plus replace any dodgy electro lytics and proceed from there if there's no excess noise. It's got two row s of red LED's to indicate stereo o/p level which still work.
easily traced to a defunct regulator IC which isn't passing on any volts and everything more less works if it's bypassed.
the right one as its data sheet specifies a minimum input volts of 17.9 but the mixer's external psu socket says only 15v.
volts input 12v output, or a LM7805, 7.5-20v input, 5 volts output.
likely ? 5v o/p seems a big drop from 15v input and so less likely; they would have used a smaller psu voltage in that case.
replies. I don't have the original PSU which would have been a a traditional heavy iron type in the day but electrically quieter than switched mode. I guess the regulator is a cheap way to cut out the 100 Hz mains ripple. The headphone o/p works fine, but the main output has a lot of hum.
side so if anything's going to fry it maybe already has. It's probably drawing less than 100mA so have no idea why the (heatsinkless) 7815 has blown, nor is it clear what the logic of repairing it with a 7815 was anyway. A 9v regulator option could well be the original, and the guy who repaired it couldn't find one so he stuck a 15v one in. Probably not a professional job then.
voltage clues like 5v IC's and go for 5v or 9v plus replace any dodgy electrolytics and proceed from there if there's no excess noise. It's got two rows of red LED's to indicate stereo o/p level which still work.
I think your logic and reasoning are wrong.
it is highly unlikely that unless it was noddy or designed to wrk frtom barreies, it would use a 9V supply trail. It is also bad logic to assume that a 15v transformer is not suitable for a 15v DC supply. It is perfect. 15VAC would have a peak out put of 1.414x15v or around 21v on load, and more off load.
The purpose of the regulator is to supply a regulated supply. Hum is less an issue really than regulation., You should be able to do away with hum by decent design. If the mixer uses opamps they will be running off +- 15V probably and that is near the limit for most. TL071/081 etc. As a designer you want th biggets rail yoiu can get to prevent overload and make usre that your signal are always much highee than the noise level - typically a few microvolts. for TL type devices. Regulation gives you the best you can do - as high as is safe for the chips.
If its designed using discrete transistors then you PROBABLY would go for up to 30V supply, but a lot of poeple just usesd a single 15V rail. Its not as good, but often it was easier to find the transformers and capacitirs for 25v rating than the next step up - 50V. Or you might stick with 2V for car battery compatibility.
I am amazed that anyone builds mixers with external power supplies too. That is very 'consumer-noddy' - most pro mixers have proper onboard mains PSUs. All of mine did.
we are assuming it has opamps., It probably dies not, since those need
+-supplies more often than not.
Oh I found a cqt diag for a PM07. jesus what a way to do it. Yup its a single 15V supply with a regulator. And the opamps all have strange ways to cope with a single sided supply. What wombat turds..
Shhessh. stick am LMN7812 or 7809 in and a 15v DC supply and be done.
o lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded wit h goods and services paid for by the confiscated wealth of a diminishing nu mber of producers.
Sounds good, probably the same as the PCM09. What's the device they use fo r a regulator in that circuit I wonder ? There aren't any smoothing caps in this box, apart from tiny 10x10 mm minia ture PCB size ones, so it must have been in the external psu. The interpre tation of what -15v is probably a bit flexible so could be as high as -15sq r(2). Can't find LM7809's, even on eBay, except from China so it's got to be an LM7812.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.