Can anybody please tell me what should the temperature (on average) be of the 12v regulator (T9) and bridge rectifier D9, in this tuner. Mine is getting up to 50.deg.C and I cannot find any faulty component. Had to replace T9 twice already.
Does anybody maybe got a service manual for this unit ?
Thanx for any assistance.
Does anybody maybe got a service manual for this unit ?
Thanx for any assistance.
Hi, I've found a to220 inside that alloy box to stop your fingers poking the mains.
The transformer runs warm about 20 degrees above ambient.
The to220 with the z heatsink runs in excess of 50 degrees C above ambient. My digital thermometer went off scale!!!
Does that help?
If we are measuring the same thing then it seems a first quality regulator is required to run permanently at these temps, what is the Tj? How about a bigger heatsink? There is just enough room, or series regulators if you fancy modifying. Conrad Johnson run their regs very hard, they claim it improves the sound!
regards Andrew T.
The transformer runs warm about 20 degrees above ambient.
The to220 with the z heatsink runs in excess of 50 degrees C above ambient. My digital thermometer went off scale!!!
Does that help?
If we are measuring the same thing then it seems a first quality regulator is required to run permanently at these temps, what is the Tj? How about a bigger heatsink? There is just enough room, or series regulators if you fancy modifying. Conrad Johnson run their regs very hard, they claim it improves the sound!
regards Andrew T.
AndrewT said:
Those temperatures are about the same as mine, so I suppose they should be like that. I just noticed that the LM7812 got a Tj of 125 and T-operating of 150 and also build in over-temperature
shutoff function. Will except it then like that - might install little CPU fan in there, just in case
Thanx for you help, appreciate.
Hum at start up
I was noticing a tiny bit of hum at start up from cold over the past couple of months.
This got gradually worse and yesterday after lying idle for two days (it quite often does not get turned off overnight) the hum was noticeably worse.
Thinking it might be the PSU not working properly I opened it up this morning.
The PCB around the 3 pins of the 12V regulator is discoloured due to excessive heat.
I measured the hum with a DMM set to 20Vac on the 18V feed to the reg, it was 2.67Vac, this axial cap almost touches the reg sink.
The hum on the 33V supply is only 23mVac or so.
Turned on the scope.
8Vpp on the first smoothing cap, 70mVpp on the second smoothing cap.
Check capacitance, the 18V is down to 566uF (this one reads as a diode on the Mega328) and the 30V is still 1050uF (mega328 says 0.2ohm esr).
Both start out as 25V 1mF 85°C
I replaced them with 25V 1mF 105°C
Now the 18V feed to the reg is 1Vpp ripple and the 33V feed is still around the 60mVpp.
Changed the sink to a 12C/W to try to get cooler operation, 7.3Vdrop across the reg.
Hum at start up is gone.
I was noticing a tiny bit of hum at start up from cold over the past couple of months.
This got gradually worse and yesterday after lying idle for two days (it quite often does not get turned off overnight) the hum was noticeably worse.
Thinking it might be the PSU not working properly I opened it up this morning.
The PCB around the 3 pins of the 12V regulator is discoloured due to excessive heat.
I measured the hum with a DMM set to 20Vac on the 18V feed to the reg, it was 2.67Vac, this axial cap almost touches the reg sink.
The hum on the 33V supply is only 23mVac or so.
Turned on the scope.
8Vpp on the first smoothing cap, 70mVpp on the second smoothing cap.
Check capacitance, the 18V is down to 566uF (this one reads as a diode on the Mega328) and the 30V is still 1050uF (mega328 says 0.2ohm esr).
Both start out as 25V 1mF 85°C
I replaced them with 25V 1mF 105°C
Now the 18V feed to the reg is 1Vpp ripple and the 33V feed is still around the 60mVpp.
Changed the sink to a 12C/W to try to get cooler operation, 7.3Vdrop across the reg.
Hum at start up is gone.
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If the desing is close to overheating and you want to reduce main voltage you may use a small power transfomer 220 volts / 24 volts to reduce main voltage to 220 volts.
Configuration shown in attachement.
If you have any question about DOT convention for a tranfomer just ask and I will help.
Configuration shown in attachement.
If you have any question about DOT convention for a tranfomer just ask and I will help.
Attachments
No need, the transformer is already selected by QUAD to suit the harmonised voltage here in Europe.
BTW,
I have enough stock of small and bigger transformer to adjust voltage using the auto-transformer concept if I wanted to.
But that will await a future project to have a mosFET switching automatic voltage select, on a big auto transformer to do the whole load on the one phase connected to my listening room and my other main audio room.
BTW,
I have enough stock of small and bigger transformer to adjust voltage using the auto-transformer concept if I wanted to.
But that will await a future project to have a mosFET switching automatic voltage select, on a big auto transformer to do the whole load on the one phase connected to my listening room and my other main audio room.
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The hot regulator has nothing to do with mains voltages or even harmonized ones. FM4 dates from the early 1980s and the mains voltage ratings match anyway, for goodness sake! . There are always going to be problems with entrenched design practices that accept hot running components because the specs allow it, though. That's been a "painful" issue with UK consumer electronics going back to the 1970s and you come to expect the hot little surprises inside their already small boxes. 
However, scorched boards, discoloured markings and embrittled insulation, solder failures etc. are not OK in my book, even if the product outlasts the owner, it's still not smart. Smart is coming up with ways to avoid the need for high temperatures and consequent power loss in the first place.
. There are always going to be problems with entrenched design practices that accept hot running components because the specs allow it, though. That's been a "painful" issue with UK consumer electronics going back to the 1970s and you come to expect the hot little surprises inside their already small boxes. However, scorched boards, discoloured markings and embrittled insulation, solder failures etc. are not OK in my book, even if the product outlasts the owner, it's still not smart. Smart is coming up with ways to avoid the need for high temperatures and consequent power loss in the first place.
According to me if you reduce mains voltage .. voltage at secondary of transformer will reduce accordingly ... ( transformer is a ratio thing )
So it will reduce voltage at the input of the regulator and reduce regulator heating.
Minimum voltage drop across regulator is around 3 Volts.... and power dissipated by regulator is proportional to voltge drop across regulator & current at output of regulator ...
So it will reduce voltage at the input of the regulator and reduce regulator heating.
Minimum voltage drop across regulator is around 3 Volts.... and power dissipated by regulator is proportional to voltge drop across regulator & current at output of regulator ...
Audiofan, the use of a bucking transformer to reduce a mains supply voltage is well known but the supply voltage discussed is not wrong. The issue is only the disappointment of realizing that the regulator was designed to run hot. Quad FM4 Manual - FM Stereo Tuner - HiFi Engine
There are 3 secondary supply windings on the transformer so reducing the AC supply voltage will affect all supplies. The DC 30V varicap tuning voltage is also strapped to the 12VDC rail and depends on it for stability. Also, a standard 3 terminal regulator differential of only 3V would be a bad mistake. The normal 5-6V accomodates most line/load fluctuations if the supply ratings are correct and application notes should be followed rather than guessing what the datasheet numbers really mean.
In short, lowering the AC supply would be the wrong approach to reducing the regulator case temperature. Simply a larger or more efficient heatsink is much simpler and more effective with fewer considerations.
There are 3 secondary supply windings on the transformer so reducing the AC supply voltage will affect all supplies. The DC 30V varicap tuning voltage is also strapped to the 12VDC rail and depends on it for stability. Also, a standard 3 terminal regulator differential of only 3V would be a bad mistake. The normal 5-6V accomodates most line/load fluctuations if the supply ratings are correct and application notes should be followed rather than guessing what the datasheet numbers really mean.
In short, lowering the AC supply would be the wrong approach to reducing the regulator case temperature. Simply a larger or more efficient heatsink is much simpler and more effective with fewer considerations.
I take it that is a tongue-in-cheek reference to high-end tube design regulation, in support of Quad's solid-state IC reg. economy.
I couldn't say what type of reg. circuit Conrad Johnson use in their products but I'd suggest the overall differences between a tube preamp and a ss tuner with a few opamps in the audio section and discrete output buffers, are plenty.
The copious distortion products of their FM detector/decoder circuits alone, would be enough to swamp any likely subtle power supply effects.
A good SOTA FM tuner can sound very satisfactory with suitable recordings and transmission but I doubt the combination with conventional tuners will ever allow us to genuinely discern the subtleties of their opamp power supplies.
I wrote 3 volts is the minimum ..... of course you need some room for mains variation and ripple on capacitor .... but if presently you have 12 or 15 volts there is some room for a voltage reduction .... if you reduce voltage drop on regulator by 40% you will reduce power dissipation by 40% and reduce elevation of temperature above ambiant of 40% all these 3 are proportional .... or almost proportional.
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