Denon DRA-375RD Capacitor ID

If that cap is on the output of a regulator, it is not critical. The main thing is not to use an electrolytic because of ESR and ESL. Any value from .01 to .22 should work, and you already know the voltage.

The unit might work with it removed, or it may be noisy, but a 7806 is a simple passive regulator, there is nothing special about the cap, only that it must be near the 7806 to keep it from oscillayting. Throw damnear anything in there. It should work.

This is small stuff, don't sweat it, hopefully this was an isolated failure and ther is no overload on the 6V line, but of course that wouldn't blow a cap, so it is likely the thing will be fixed.

I would replace the regulator, not because it might be shorted, 7806s are rarely fed with more than 12V an it's rare to see a cap of that type with a lower voltage rating than 50V. However, the cap might have been shorted and stressed the 7806, so for 44 cents I would replace it as well.

JURB

On Thu, 23 Aug 2007 21:04:08 -0700, snipped-for-privacy@gmail.com put finger to keyboard and composed:

0.1F 5.5V sounds like a "gold" cap. These are normally used for backup. I've never seen a rectangular one, though.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

I'm pretty sure that I did see a rectangular one once, but whatever, if it is 0.1F at 5.5v, it is *not* just any old cap put there to stop the regulator oscillating - it is definitely a goldcap for backup. Are you sure that there is not a diode between the regulator's output, and the cap? And a

7806 is not 'passive'. The 78 series regs are very much active shunt types, containing a feedback controlled regulator drive circuit, that maintains very close tolerance on the output voltage, and provides significant ripple rejection of the order of 80dB as I recall. They also contain circuitry to protect against shorts, providing voltage foldback in the event of an excess current condition, and thermal shutdown for excess temperature conditions.

Arfa

Yes - the output stability cap would be something like a 0.1uF ceramic.

Hmm, I thought it was a direct connection (via jumper), but I'll double check that. There is a "+5V" silkscreen label in that general area, which brings up another possibility - perhaps that regulator is supposed to be a 7805. I'm working on getting the schematic, that should clear things up.

TM

I guess it will. I have seen 7806's used with a diode and goldcap. The diode drops the rail to around 5.3v, and also ensures that there is no reverse leakage path from the backup cap through the regulator to ground. Most system control micros are quite happy with a rail of just over 5v, and lots of hifis have got such a voltage on the 'nominal' 5v rail.

Arfa

On Fri, 24 Aug 2007 17:12:34 GMT, "Arfa Daily" put finger to keyboard and composed:

A 7805/7806 in a TO220 package would be rated at 1A. How long would a

0.1F cap be able to supply such a load, or even a 100mA load?

Then again, maybe the 7806 regulator supplies the bulk of the 6V logic while a diode-isolated gold cap powers some volatile RAM?

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

That's the usual arrangement, which is part of the reason that I asked about the diode. Often it's just the system control micro that has memory maintenance power supplied to it from the backup cap via a separate pin.

Arfa

Spot on. I looked at the board again, and found two branches of the circuit from the 7806 output pin. One goes through a 4.7ohm resistor, then a diode, then to the positive pin of the 0.1F cap and a pin on the connector to the front panel. The other branch goes through a diode, then to a BA6208 (driver for the volume pot motor?) and perhaps the front-end daughtercard.

Looking at DigiKey, it appears that Panasonic (Gold), CooperBussmann (Aerogel), and Elna all have comparable supercap replacements. Any recommendations? I'm considering paying extra for the Elna DH-5R5D104T, since it's rated to 85C.

Thanks again, Tony

Of those three, the only one that I've had personal experience of, is the Panasonic, but they seem to be a component that might well be 'the more ya pays, the better ya gets'. In any event, the higher temperature rating cap is probably not a bad idea. I've never really looked at the temperature rating of them, so I've no idea what the 'standard' is. 85 deg is certainly the norm for 'bog standard' electrolytics, with 105 deg being 'high temp' ones. When you do come to replace it, I might feel inclined to replace any

0.1uF and small electrolytic that might be glued across the output of the 7806, just in case they have failed, and the goldcap is working hard to suppress any tendency to instability of the reg, as well as carrying out its primary backup function. I don't imagine that they would be very good at handling high frequency ripple, and they might well warm up, which might be what you saw in the original being split open. It would be worth checking the feed diode as well, to make sure that it has not failed short, or gone leaky, resulting in greater than the max 5.5v rating of the cap, being applied across it. I think as a final check before wrapping it up and calling it a draw, I would just monitor the (power on) voltage across that cap for a couple of hours, just in case there is any issue with the reg output voltage, once it gets thoroughly warmed through.

Arfa