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Old 27th November 2004, 01:48 PM   #1
JDeV is offline JDeV  South Africa
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Default Quad FM4 problem

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.
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Old 27th November 2004, 05:36 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
I'll go & open mine up. It's been playing for the last couple of hours.
Tell me where to find the components.
regards Andrew T.
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Old 28th November 2004, 08:37 AM   #3
JDeV is offline JDeV  South Africa
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Quote:
Originally posted by AndrewT
Hi,
I'll go & open mine up. It's been playing for the last couple of hours.
Tell me where to find the components.
regards Andrew T.
Hi Andrew,
Those components are underneath the cover in the corner where the mains cable plug in.
See attached pic.
I suspect your's wont have the little heatsink, I fitted that to help with heat problem in the meantime.
Thanx for assistance.
Attached Images
File Type: gif fm4.gif (76.8 KB, 154 views)
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Old 28th November 2004, 08:42 AM   #4
AndrewT is offline AndrewT  Scotland
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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.
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Old 28th November 2004, 09:04 AM   #5
JDeV is offline JDeV  South Africa
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Join Date: Oct 2002
Location: Cape Town
Quote:
Originally posted by AndrewT
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.
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.
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Old 15th December 2014, 01:43 PM   #6
AndrewT is offline AndrewT  Scotland
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Default 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.
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Last edited by AndrewT; 15th December 2014 at 01:57 PM.
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Old 15th December 2014, 01:57 PM   #7
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Have you check power line voltage ?? ( mains voltage )

If voltage is to high it is the regulator that will pay the price ......

I would also check voltage drop across voltage regulator ...
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Old 15th December 2014, 01:58 PM   #8
AndrewT is offline AndrewT  Scotland
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the mains was at 244Vac while I had the safety protection cover removed.
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Old 15th December 2014, 02:00 PM   #9
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Is nominal voltage printed on nameplate ??
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Old 15th December 2014, 02:04 PM   #10
AndrewT is offline AndrewT  Scotland
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It's for the UK and the the harmonised european voltage.
So it's designed to operate over the full range of 216Vac to 253Vac.

And it has a diagram inside showing the link positions for either 110/120Vac, or 220/240Vac, with the 220/240Vac position ticked with the inspector's marker pen.
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