Denon DRA-375RD Capacitor ID

[[email protected]]

At site C401 of main board. Cap is some kind of polymer electrolytic,
but rectangular, not cylindrical. Roughly 9/16"H x 1/2"W x 1/4"D,
black plastic case,
with flat sheets of polymer/plastic inside. Markings as follows:

S 5.5V
0.1F
- 6A +

This is on the output of a 7806 regulator (IC401). Cap was cracked,
regulator ran warm but works out of circuit. Did Denon actually intend
to use a 5.5V cap on a 6V rail, or is this an incorrect substitution?
Solder joints on cap appear to be factory, but the silkscreen for this
part is round.

Thanks,
Tony

 

[[email protected]]

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

 

[Franc Zabkar]

At site C401 of main board. Cap is some kind of polymer electrolytic,
but rectangular, not cylindrical. Roughly 9/16"H x 1/2"W x 1/4"D,
black plastic case,
with flat sheets of polymer/plastic inside. Markings as follows:

S 5.5V
0.1F
- 6A +

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

This is on the output of a 7806 regulator (IC401). Cap was cracked,
regulator ran warm but works out of circuit. Did Denon actually intend
to use a 5.5V cap on a 6V rail, or is this an incorrect substitution?
Solder joints on cap appear to be factory, but the silkscreen for this
part is round.

Thanks,
Tony

- Franc Zabkar

 

[Arfa Daily]

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

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

 

[[email protected]]

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.

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

Are you sure that there is not a diode between the regulator's output,
and the cap?

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

 

[Arfa Daily]

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

 

[Franc Zabkar]

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

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

 

[Arfa Daily]

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

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

 

[[email protected]]

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

 

[Arfa Daily]

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