[obcbeatle]

Hello:

I have a HK A-402 amp that I have been using since the 70's. The left
channel recently started to lose volume and sometimes renders no volume
at all. I can depress the Tone Defeat switch on the 402 front panel to
sometimes get the left channel signal back, but it still usually is not
as loud as the right channel. Also, it usually reverts back to
rendering little to no volume, over time. Does this sound like
something a little compressed air and cleaner (Deoxit?) might cure? I
have never had any problems with this amp so I've never cleaned it or
had it serviced. I'm sure it is pretty dusty inside though. TIA.

[JANA]

You should apply a little contact control cleaner to the switch and work it
in. You can get the proper contact cleaner at most any electronics parts
supplier. If it is not a switch contact problem, most likely it can be a
cold solder connection, or something is failing.

--

JANA
_____


"obcbeatle" wrote in message
ups.com...
Hello:

I have a HK A-402 amp that I have been using since the 70's. The left
channel recently started to lose volume and sometimes renders no volume
at all. I can depress the Tone Defeat switch on the 402 front panel to
sometimes get the left channel signal back, but it still usually is not
as loud as the right channel. Also, it usually reverts back to
rendering little to no volume, over time. Does this sound like
something a little compressed air and cleaner (Deoxit?) might cure? I
have never had any problems with this amp so I've never cleaned it or
had it serviced. I'm sure it is pretty dusty inside though. TIA.

[obcbeatle]

JANA wrote:
You should apply a little contact control cleaner to the switch and work it
in. You can get the proper contact cleaner at most any electronics parts
supplier. If it is not a switch contact problem, most likely it can be a
cold solder connection, or something is failing.

Thanks for the quick reply. I'll pick up some contact cleaner tomorrow
and give that a shot. How do you visually identify a cold solder
connection? Thanks.

[Richard Crowley]

"obcbeatle" wrote in...
JANA wrote:
You should apply a little contact control cleaner to the switch and
work it
in. You can get the proper contact cleaner at most any electronics
parts
supplier. If it is not a switch contact problem, most likely it can
be a
cold solder connection, or something is failing.

Thanks for the quick reply. I'll pick up some contact cleaner
tomorrow
and give that a shot. How do you visually identify a cold solder
connection? Thanks.

Frequently it cannot be identified visually. A common
debugging technique is to poke around with an insulating
probe to see if you can cause/control the intermittency.

In ages past you could get an "orange stick" that looked
like a small pencil with one diagonal end, and one sharp
end. Made of wood. Maybe they have plastic ones now?

[Chuck]

On 26 Dec 2006 18:49:56 -0800, "obcbeatle"
wrote:

Hello:

I have a HK A-402 amp that I have been using since the 70's. The left
channel recently started to lose volume and sometimes renders no volume
at all. I can depress the Tone Defeat switch on the 402 front panel to
sometimes get the left channel signal back, but it still usually is not
as loud as the right channel. Also, it usually reverts back to
rendering little to no volume, over time. Does this sound like
something a little compressed air and cleaner (Deoxit?) might cure? I
have never had any problems with this amp so I've never cleaned it or
had it serviced. I'm sure it is pretty dusty inside though. TIA.


This model is known for that switch causing the problem you are
experiencing. I'd buy some Caig Deoxit 5 and spray the switch
contacts. If you don't want to disassemble the amp, a spray through
the gap around the button on the front panel may suffice. Chuck

[obcbeatle]

Chuck wrote:

This model is known for that switch causing the problem you are
experiencing. I'd buy some Caig Deoxit 5 and spray the switch
contacts. If you don't want to disassemble the amp, a spray through
the gap around the button on the front panel may suffice. Chuck

Thanks for all the replies. Indeed that is exactly what I did and the
problem went away! Many thanks to all that replied. Not only does the
left channel work normally again, but both channels seem louder after
working the Deoxit into that switch. This HK A-402 is still one awesom
amp!

I'm now having a problem with my HK HD500 cd player. I will explain
the problem in a seperate post, although I not certain the problem wil
be fixable. At least by me anyway Thanks again.

[obcbeatle]

obcbeatle wrote:

Chuck wrote:

This model is known for that switch causing the problem you are
experiencing. I'd buy some Caig Deoxit 5 and spray the switch
contacts. If you don't want to disassemble the amp, a spray through
the gap around the button on the front panel may suffice. Chuck

Thanks for all the replies. Indeed that is exactly what I did and the
problem went away! Many thanks to all that replied. Not only does the
left channel work normally again, but both channels seem louder after
working the Deoxit into that switch. This HK A-402 is still one awesom
amp!

Well...I guess I spoke too soon. Since I posted last night the left
chanel has decided to go weak again. Interestingly, I have sprayed the
Deoxit a few times since, and each time I spray it fixes the problem
only for the left chanell to eventually go weak again. Sometimes after
an hour, sometimes after a few hours. Maybe it's a heat related issue?
Maybe the switch itself is bad? If I can't get the 402 working
correctly again I may just buy another "twin amp" integrated amplifier.
Although, I will sure miss this 402 Any suggestions on websites
that rate 40-45 watt twin amp integrated stereo amplifiers like the
402? Or amp suggesstions in general? I assume twin amp amplifiers are
still considered the way to go, or has the technology changed over the
years? I currently plug in the following devices to the 402; PC,
turntable, cassette deck, 4 track cassette recorder, and cd player. I
have been recording my LP collection to .mp3's, until the left channel
problem. TIA.

[Dave Platt]

In article . com,
obcbeatle wrote:

Well...I guess I spoke too soon. Since I posted last night the left
chanel has decided to go weak again. Interestingly, I have sprayed the
Deoxit a few times since, and each time I spray it fixes the problem
only for the left chanell to eventually go weak again. Sometimes after
an hour, sometimes after a few hours. Maybe it's a heat related issue?
Maybe the switch itself is bad?

It's quite possible that the switch itself is failing, due to either
contact wear, or to metal fatigue in the contacts.

If I can't get the 402 working
correctly again I may just buy another "twin amp" integrated amplifier.
Although, I will sure miss this 402

It's conceivable that you could find a replacement switch... either an
OEM part (although that's not all that likely these days) or a standard-
form-factor switch which could be mounted on the front panel and wired
to the original switch's contact pads.

Failing that, if you don't really need the switch functions, a
technician could probably unsolder the switch and simply install wire
jumpers across several of the pads (shorting together the pads which
would normally be shorted by the switch when it's in the normal-use
position).

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[obcbeatle]

Dave Platt wrote:

It's quite possible that the switch itself is failing, due to either
contact wear, or to metal fatigue in the contacts.

It's conceivable that you could find a replacement switch... either an
OEM part (although that's not all that likely these days) or a standard-
form-factor switch which could be mounted on the front panel and wired
to the original switch's contact pads.

Failing that, if you don't really need the switch functions, a
technician could probably unsolder the switch and simply install wire
jumpers across several of the pads (shorting together the pads which
would normally be shorted by the switch when it's in the normal-use
position).

Thanks for the quick reply Dave. I really don't need the Tone Defeat
switch, so that sounds like a good idea (unsoldering...). It's funny
because up until now I don't even remember using that switch. So for
it to fail first seems rather odd when compared to the amount of times
I've used the Tape 1 switch, for instance. But alas... One thing I
just noticed when I was moving the 402. I accidently bumped the 402
while it was on and playing. All of a sudden the left channel came
alive again (volume boost). I can replicate that behavior by gently
bumping the amp. The left channel volume leveI will increase.
Unfortunately, over time it weakens again Anyway...I may try to
find someone to service this amp. Unfortunately, I live in rural
Vermont and don't know how many good electronic tech's work around here
I've done some minor electronic repair on my guitar pedals and tube
amp (soldering wires and replacing caps.) but I don't have a schematic
for the 402 and it looks a little difficult to get the PCB (where the
switch lives) off the 402 to do any work. Thanks again for the
assistance.

[Dave Platt]

In article . com,
obcbeatle wrote:

Thanks for the quick reply Dave. I really don't need the Tone Defeat
switch, so that sounds like a good idea (unsoldering...). It's funny
because up until now I don't even remember using that switch. So for
it to fail first seems rather odd when compared to the amount of times
I've used the Tape 1 switch, for instance. But alas... One thing I
just noticed when I was moving the 402. I accidently bumped the 402
while it was on and playing. All of a sudden the left channel came
alive again (volume boost). I can replicate that behavior by gently
bumping the amp. The left channel volume leveI will increase.
Unfortunately, over time it weakens again

That sounds as if you've got a loose connection or a failed ("cold"
or broken) solder joint somewhere inside. One can get all sorts of
intermittent behaviors (changed by time, heat, impact/vibration,
phase of moon, etc.) from those sorts of problems.

Not fun to debug, but very satisfying when you do find 'em.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[Mark D. Zacharias]

Dave Platt wrote:
In article . com,
obcbeatle wrote:

Thanks for the quick reply Dave. I really don't need the Tone Defeat
switch, so that sounds like a good idea (unsoldering...). It's funny
because up until now I don't even remember using that switch. So for
it to fail first seems rather odd when compared to the amount of
times I've used the Tape 1 switch, for instance. But alas... One
thing I just noticed when I was moving the 402. I accidently bumped
the 402 while it was on and playing. All of a sudden the left
channel came alive again (volume boost). I can replicate that
behavior by gently bumping the amp. The left channel volume leveI
will increase. Unfortunately, over time it weakens again

That sounds as if you've got a loose connection or a failed ("cold"
or broken) solder joint somewhere inside. One can get all sorts of
intermittent behaviors (changed by time, heat, impact/vibration,
phase of moon, etc.) from those sorts of problems.

Not fun to debug, but very satisfying when you do find 'em.

I'm thinking the OP just did not get the cleaner where it needed to be - at
the switch contacts. These HK switches are flaky indeed, but should work for
months to a year or more after cleaning.

Mark Z.

[obcbeatle]

Dave Platt wrote:
That sounds as if you've got a loose connection or a failed ("cold"
or broken) solder joint somewhere inside. One can get all sorts of
intermittent behaviors (changed by time, heat, impact/vibration,
phase of moon, etc.) from those sorts of problems.

Not fun to debug, but very satisfying when you do find 'em.

Mark D. Zacharias wrote:

I'm thinking the OP just did not get the cleaner where it needed to be - at
the switch contacts. These HK switches are flaky indeed, but should work for
months to a year or more after cleaning.


OK...I bit the bullet this evening, took the cover off and used a can
of compressed air to gingerly spray all the dust out of the HK A-402.
Then I sprayed every switch and pot. with Deoxit and worked it in real
good. When I plugged everything back in I had no signal in the left
channel until I depressed the Low Filter switch on/off. So now it is
working normally, but for how long, I do not know. Also, this morning
when I turned the 402 on there was a hiss coming from the left channel.
The hiss stopped after about 3-4 minutes, but the left channel was
weak again. That is what prompted me to spray all the switches/pots
this evening. They'd never been touched anyway, so I thought maybe....
Why the Low Filter switch was effecting the left channel, I do not
know. So it appears that the Low Filter and Tone Defeat switches BOTH
may be effecting the left channel. And I'm now wondering what the
hissing is that I heard this morning in the left channel, until it
warmed up. It did NOT hiss when I turned the 402 on this evening,
AFTER spraying all the switches/pots. with Deoxit. I hope when I turn
off the 402 tonight and back on tomorrow morning everything is normal
If not, I may prod for a loose connection. Thanks for all your
help.