Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old March 20th 18, 08:01 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

I have had this beast for about 10 years now, and it has developed a specific symptom - the right channel will cut out entirely - silent-same-as-no-signal on occasion. No pop, no prior acting out, no distortion. Otherwise, no issues.

On the output board is a DPST NC 24V reed relay. Meaning (to me) that when it goes into protection-mode, the relay gets energized and output is cut. The schematic (HI-FI Engine) seems to bear this out.

Picture of board here - down the page. http://members.quicknet.nl/gerard.sl...citation17.htm

There seem to be a number of versions of this relay. Additional part-numbers a 200-002-7610 and 328-46-B

Questions: Anyone else with this symptom in this device? I would hate to replace the relay only to find that something else is going on and the system is doing its job.

And, may I substitute any decent 24V DPST relay? I have lots of room to play around.

Other notes:

a) It is paired with a Citation 19 power-amp, acquired separately.
b) I have recapped the power-supply, and the output voltages are as they should be.
c) The unit dates c. 1978

Thanks in advance!

Peter Wieck
Melrose Park, PA

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Old March 20th 18, 08:37 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

Update: Computer Components is still in business and has ten (10) pieces in stock made in 1978. They are testing them with the intent of sending me two - at a price, of course.

But, I am still wanting to figure out if this is the most likely issue - or should I be looking beyond.

Peter Wieck
Melrose Park, PA
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Old March 20th 18, 08:38 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent


In article ,
wrote:

I have had this beast for about 10 years now, and it has developed a specific symptom - the right channel will cut out entirely - silent-same-as-no-signal on occasion. No pop, no prior acting out, no distortion.
Otherwise, no issues.

On the output board is a DPST NC 24V reed relay. Meaning (to me)
that when it goes into protection-mode, the relay gets energized and
output is cut. The schematic (HI-FI Engine) seems to bear this out.


No, it looks to me as if the circuit works the other way around. The
relay is designed to short the output signal to ground *until* the
relay is energized. During normal listening, the relay is energized,
the contacts are open, and the relay "vanishes" from the audio path.

Take a look at how the relay is driven/controlled, from an auxiliary
output on the power supply board.

Picture of board here - down the page.
http://members.quicknet.nl/gerard.sl...citation17.htm

There seem to be a number of versions of this relay. Additional part-numbers a 200-002-7610 and 328-46-B

Questions: Anyone else with this symptom in this device? I would hate to replace the relay only to find that something else is going on and the system is doing its job.


Don't have one myself. Here are my thoughts, for what little they may
be worth.

Since the relay is a DPST single-coil, and only one of the two
channels is affected, it seems unlikely that the relay drive is
bad... if it were, both contacts would drop to NC simultaneously and
both output signals would be shorted to ground. So, if it's a fault
in the relay, it must be in the contacts for that one channel -
somehow they're sticking closed. I'd be more likely to suspect a
reed-relay fault where the contacts _don't_ close properly (due
to e.g. lack of contact self-wiping, or the use of a standard reed
relay which requires a wetting current when you'd really want a dry
relay) and that doesn't seem to be the case here.

It _could_ be a case where you've got inadequate current drive to the
relay, and for some reason this affects only one of the two reeds, but
that seems less likely.

I think the first thing I'd suggest, for practical trouble-shooting,
would be to catch the problem when it exists, and then trace the
signal through the output board... see if you've got audio at J1/3 and
then follow it through the output driver and see where it disappears.

And, may I substitute any decent 24V DPST relay? I have lots of room to play around.


It doesn't look to me as if the protection circuit is at all
sophisticated... the relay is driven from a simple time-delay circuit
which is driven by the +24 regulated supply. The relay driver is an
MPSA13, which is good for 500 mA continuous. The relay itself is just
a short-to-ground NC and the contacts aren't in the normal audio
signal path at all. So, it doesn't look very critical to me... any
small DPST-NC or DPDT 24-volt DC relay would probably serve (just
remember to keep the diode across the coil!)

b) I have recapped the power-supply, and the output voltages are as
they should be.


Other possible faults would be a bad 'lytic in the signal path (I've
occasionally seen them go entirely open), or bad switch contacts (input
selector, tape-monitor, etc.), or a broken solder joint that's
undergoing thermal cycling. The "tap the boards with a chopstick"
technique might help pin down the location of the fault.

I think a signal-tracing exercise would be a good idea, before you
replace anything.

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Old March 20th 18, 08:55 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

Dave:

You are right on the relay operation - I should have caught that - and it makes sense that a power-drop would also drop output.

I will signal-trace, but given the symptoms, and with proper understanding of the relay operation, I am even more suspicious of the relay. Most of the caps are new (less than 10 years) and the switches, contacts and input jacks are clean. But, testing leads to better understanding - all good.

Thanks for your suggestions!

Peter Wieck
Melrose Park, PA
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Old March 20th 18, 09:05 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

On Tuesday, March 20, 2018 at 3:55:37 PM UTC-4, wrote:
Dave:

You are right on the relay operation - I should have caught that - and it makes sense that a power-drop would also drop output.

I will signal-trace, but given the symptoms, and with proper understanding of the relay operation, I am even more suspicious of the relay. Most of the caps are new (less than 10 years) and the switches, contacts and input jacks are clean. But, testing leads to better understanding - all good.

Thanks for your suggestions!

Peter Wieck
Melrose Park, PA



Many years ago I saw just one DPST protection relay go bad, but it would cause a noisy output or intermittent crackles as the volume was raised as one set of contacts were pitted.

But otherwise I'd say if one side is good, it's most likely not the relay as Dave pointed out. The best you can hope for is that it quits entirely. Nothing is easier than tracing a mute audio channel when there's a working one right along side of it, and nothing is worse than chasing an intermittent audio channel when it's working..





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Old March 20th 18, 09:20 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

On Tuesday, March 20, 2018 at 4:05:27 PM UTC-4, John-Del wrote:

Many years ago I saw just one DPST protection relay go bad, but it would cause a noisy output or intermittent crackles as the volume was raised as one set of contacts were pitted.

But otherwise I'd say if one side is good, it's most likely not the relay as Dave pointed out. The best you can hope for is that it quits entirely. Nothing is easier than tracing a mute audio channel when there's a working one right along side of it, and nothing is worse than chasing an intermittent audio channel when it's working..


The first test will be that wooden peg on the relay. Agreed that the quiet failure does not lead to the relay first thing.

Peter Wieck
Melrose Park, PA
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Old March 21st 18, 03:40 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

On 03/20/18 15:01, wrote:
I have had this beast for about 10 years now, and it has developed a specific symptom - the right channel will cut out entirely - silent-same-as-no-signal on occasion. No pop, no prior acting out, no distortion. Otherwise, no issues.

On the output board is a DPST NC 24V reed relay. Meaning (to me) that when it goes into protection-mode, the relay gets energized and output is cut. The schematic (HI-FI Engine) seems to bear this out.

Picture of board here - down the page.
http://members.quicknet.nl/gerard.sl...citation17.htm

There seem to be a number of versions of this relay. Additional part-numbers a 200-002-7610 and 328-46-B

Questions: Anyone else with this symptom in this device? I would hate to replace the relay only to find that something else is going on and the system is doing its job.

And, may I substitute any decent 24V DPST relay? I have lots of room to play around.

Other notes:

a) It is paired with a Citation 19 power-amp, acquired separately.
b) I have recapped the power-supply, and the output voltages are as they should be.
c) The unit dates c. 1978

Thanks in advance!

Peter Wieck
Melrose Park, PA


Seems easy to test--work the relay a few times, hit it with a
screwdriver, hair dryer, cold spray....

Cheers

Phil Hobbs
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Old March 22nd 18, 05:25 AM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

I've had bad contacts on relays before. Both audio equipment and a programmable power supply. To fix the power supply, I wrote a program to open/close the relay every 10s overnight and the problem went away.

I'd measure the DC at the speaker terminals before and during a fault first.
I'd expect something initially and probably zero if your loosing contact.

Then do the same, but before the relay.
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Old March 22nd 18, 07:31 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

On Thursday, March 22, 2018 at 12:25:55 AM UTC-4, Ron D. wrote:
I've had bad contacts on relays before. Both audio equipment and a programmable power supply. To fix the power supply, I wrote a program to open/close the relay every 10s overnight and the problem went away.

I'd measure the DC at the speaker terminals before and during a fault first.
I'd expect something initially and probably zero if your loosing contact.

Then do the same, but before the relay.


He won't be picking up any dc on the outputs. The other channel remains. If it was a DC fault detect, the relay would open and both sides would go out.

Besides, the DC detect is hair trigger on these and the meter probably wouldn't resolve the value before the relay opened. A min/max peak recorder feature on the dmm might catch it but even that isn't guaranteed.

The easiest thing to do if the relay is suspected is to thwack it while the channel is out (but not hard enough to bounce to effect a contact bounce). If the contacts are gimpy, something will be heard on the mute channel.

The problem could be anywhere. If he has pre amp in/out jumpers on the back panel, he could remove them and put in short RCA cables and cross them to see if the drop out moves to the other side. If so, it's before the junction, if not, it's after.

The easiest thing to do is trace it with a scope when the channel acts up. The problem is that once you get near an intermittent circuit with a scope probe, the problem clears up..
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Old March 22nd 18, 08:05 PM posted to sci.electronics.repair
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Default Harman Kardon Citation 17 Pre-Amp One Channel Intermittent

This weekend will be the testing. A new relay (exact fit) is $80 from the same company that made them for HK. Not bad for an obsolete part. but about 10X the cost of a similar unit. But the gentleman at Computer Components stated that their manufacturing specs called for "matched reeds".

The relay is also large enough to open and have a look.

Peter Wieck
Melrose Park, PA


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