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KPA100 problem

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n0jrn

KPA100 problem

Gang: I need some advise please.

I'm trying to finish my KPA100 but I can't seem to get beyond voltage tests
on page 46 of the manual.

I should be getting 90 to 150 V's at the junction of C77 & R11 but only
getting 47 volts.

I should be getting -5 to -25 V's at pin 8 of U4 BUT I'm only
seeing -4.1.

I did some research in the archives and came up with a few ideas. Checked
D1 - D8 and T3 pads. All diodes pass continuity test and T3 seems fine and
shows zero resistance between pads.

Checking the schematics prompted me to lift the anode of D7 to remove U4.
In doing this, the voltage at the junction of R11 came up into spec and
shows 150 V's.

This means that U4 is drawing the circuit down. SO, I sent Elecraft an
e-mail and Gary sent me a new MAX1406. Figured I would install it
and all would be good. NOT !

After installing the new U4, I rechecked voltage at R11 and found it is
still just 47 V's.

I've double checked orientation of U4, and it's fine. I was very careful
to observe anti static procedures when installing the new chip. SO, I'm
confused and not sure where to go from here.

Any advise would be greatly appreciated.

Thanks & 72: Jerry N0JRN

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Don Wilhelm-4

Re: KPA100 problem

Jerry,

That means U4 is not the problem, the problem is somewhere in the
rectifier stack and goes away when you lift the anode of D7.

Check both D7 and D8 for proper orientation (use the parts placement
diagram since the board silkscreen is covered). Check for a solder
bridge across the leads of C38. Be certain C35 is soldered properly.
If you lift the anode of D7 and place a 0.1 uF capacitor from the
"flying lead" of D7 to ground, what is the voltage at the D7 anode?

I know that did not fully identify the failure point, but hopefully it
gives you some clues.

73,
Don W3FPR

n0jrn wrote:

> Gang: I need some advise please.
>
> I'm trying to finish my KPA100 but I can't seem to get beyond voltage tests
> on page 46 of the manual.
>
> I should be getting 90 to 150 V's at the junction of C77 & R11 but only
> getting 47 volts.
>
> I should be getting -5 to -25 V's at pin 8 of U4 BUT I'm only
> seeing -4.1.
>
> I did some research in the archives and came up with a few ideas. Checked
> D1 - D8 and T3 pads. All diodes pass continuity test and T3 seems fine and
> shows zero resistance between pads.
>
> Checking the schematics prompted me to lift the anode of D7 to remove U4.
> In doing this, the voltage at the junction of R11 came up into spec and
> shows 150 V's.
>
> This means that U4 is drawing the circuit down. SO, I sent Elecraft an
> e-mail and Gary sent me a new MAX1406. Figured I would install it
> and all would be good. NOT !
>
> After installing the new U4, I rechecked voltage at R11 and found it is
> still just 47 V's.
>
> I've double checked orientation of U4, and it's fine. I was very careful
> to observe anti static procedures when installing the new chip. SO, I'm
> confused and not sure where to go from here.
>
> Any advise would be greatly appreciated.
>
> Thanks & 72: Jerry N0JRN
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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>
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>
>

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Andrew UK

Re: KPA100 problem

Hi Jerry,

I had the same problem and suspected U4, I removed U4 and fitted and IC holder, and then fitted a new IC and still had the same fault.

The problem turned out to be a cracked capacitor in the voltage magnification line. The Capacitor spacing is a bit smaller than the holes provided and I had used too much force getting the component flat.

There are not many conponents to check. make sure you have a good desoldering tool.

73's

Andrew

PS Merry Christmas Jerry and Don

Don Wilhelm-4 wrote

Jerry,

That means U4 is not the problem, the problem is somewhere in the
rectifier stack and goes away when you lift the anode of D7.

Check both D7 and D8 for proper orientation (use the parts placement
diagram since the board silkscreen is covered). Check for a solder
bridge across the leads of C38. Be certain C35 is soldered properly.
If you lift the anode of D7 and place a 0.1 uF capacitor from the
"flying lead" of D7 to ground, what is the voltage at the D7 anode?

I know that did not fully identify the failure point, but hopefully it
gives you some clues.

73,
Don W3FPR

n0jrn wrote:
> Gang: I need some advise please.
>
> I'm trying to finish my KPA100 but I can't seem to get beyond voltage tests
> on page 46 of the manual.
>
> I should be getting 90 to 150 V's at the junction of C77 & R11 but only
> getting 47 volts.
>
> I should be getting -5 to -25 V's at pin 8 of U4 BUT I'm only
> seeing -4.1.
>
> I did some research in the archives and came up with a few ideas. Checked
> D1 - D8 and T3 pads. All diodes pass continuity test and T3 seems fine and
> shows zero resistance between pads.
>
> Checking the schematics prompted me to lift the anode of D7 to remove U4.
> In doing this, the voltage at the junction of R11 came up into spec and
> shows 150 V's.
>
> This means that U4 is drawing the circuit down. SO, I sent Elecraft an
> e-mail and Gary sent me a new MAX1406. Figured I would install it
> and all would be good. NOT !
>
> After installing the new U4, I rechecked voltage at R11 and found it is
> still just 47 V's.
>
> I've double checked orientation of U4, and it's fine. I was very careful
> to observe anti static procedures when installing the new chip. SO, I'm
> confused and not sure where to go from here.
>
> Any advise would be greatly appreciated.
>
> Thanks & 72: Jerry N0JRN
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft@mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.716 / Virus Database: 270.14.105/2562 - Release Date: 12/13/09 02:39:00
>
>
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n0jrn

Re: KPA100 problem

In reply to this post by n0jrn

Good Morning Don / Andrew:

I very much appreciate both your suggestions.

DON: I do have the KPA100UPKT installed and R4 is 100K. So, I
will lift D8 and see what results I get.

BUT first, I'll check the caps in the rectifier section as Andrew
suggests to make sure all is well there.

Now to call Mouser and get another MAX1406 on the way............

Thanks guys and I'll keep you up on how things work out.

72 Jerry N0JRN
On 12/14/2009 6:22:37 AM, Don Wilhelm ([hidden email]) wrote:

> Jerry,
>
> I will take back what I said about U4 - it is faulty.
> That negative voltage is there only to allow the RS-232 drivers to
> produce a negative level, the current draw should be minimal.
> The only thing U4 does is convert RS-232 levels to TTL levels and
> vice-versa.
>
> Actually -28 volts is a bit much and does exceed the maximum speced
> voltage for the chip. -12 volts is more than sufficient and even -5
> volts is OK, so lowering the voltage a bit will help with the life of
> the chip.
> Do you have the KPA100UPKT installed (look for blue toroid cores at L16
> and RFC1)? If installed, change R4 to 100k if it is not already.
> If R4 is already 100k or you have red toroid cores at L15 and L16,
> remove D8 to drop the negative voltage to about half its present value.
>
> The KPA100 amplifier will function fine without U4 installed, but you
> will not be able to use the RS-232 portion of the AUX I//O connector.
>
> 73,
> Don W3FPR

n0jrn

Re: KPA100 problem

In reply to this post by n0jrn

Don:

Just to clarify !

The -28V's I'm seeing at pin 8 of U4 is measured without the IC installed.

Lets say for the sake of conversation that I install a good MAX1406 and it
draws on the rectifier circuit a minimal amount.

Would / could that bring the -28V's back into specs for this chip???. ( I
have to figure Wayne designed the circuit taking this draw into
consideration )

OR is my -28V's so abnormal that I need to be looking at other issues
in my rectifier pack to bring this negative voltage back into spec ???

Could the negative voltage I'm getting be responsible for damaging this chip
???

I have 2 new chips coming from Mouser. I'm not installing them until I'm
satisfied that I've checked and double checked EVERYTHING involved.

Thanks again and happy holidays to the group:

72 Jerry N0JRN
----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "n0jrn" <[hidden email]>
Sent: Monday, December 14, 2009 6:22 AM
Subject: Re: [Elecraft] KPA100 problem

> Jerry,
>
> I will take back what I said about U4 - it is faulty.
> That negative voltage is there only to allow the RS-232 drivers to produce
> a negative level, the current draw should be minimal.
> The only thing U4 does is convert RS-232 levels to TTL levels and
> vice-versa.
>
> Actually -28 volts is a bit much and does exceed the maximum speced
> voltage for the chip. -12 volts is more than sufficient and even -5

Don Wilhelm-4

Re: KPA100 problem

Jerry,

That answer depends on which set of "specifications" you want to believe.

I am saying that the Absolute Maximum Specification for the Maxim
MAX1406 for Vss (pin 8) is -14 volts - you can check the data sheet for
yourself. Yes, many KPA100s exceed that value - note that the KPA100 DC
voltage chart lists the nominal voltage at U4 pin 8 at -22 volts.
Whether that is a cause for failure of the chip is reason for
speculation, there is not enough data to say yeah or nay. .
What I have offered is a way to reduce the Vss voltage to the MAX1406
without also reducing the bias voltage to the KPA100 T/R switch. That
involves removing D8, and D8 alone. The data sheet Electrical
Characteristics current for pin 8 (Iss) is typical 185 uA with a maximum
of 500 uA. for a Vss of -13.2 volts Minimum to -10.8 Maximum - that is
not a lot of current draw on that pin.

I am stating that a Vss (U4 pin 8) voltage less than -14 volts exceeds
the Absolute Maximum Voltage rating per the MAX1406 datasheet - nothing
more and nothing less.

73,
Don W3FPR

n0jrn wrote:

> Don:
>
> Just to clarify !
>
> The -28V's I'm seeing at pin 8 of U4 is measured without the IC installed.
>
> Lets say for the sake of conversation that I install a good MAX1406 and it
> draws on the rectifier circuit a minimal amount.
>
> Would / could that bring the -28V's back into specs for this chip???. ( I
> have to figure Wayne designed the circuit taking this draw into
> consideration )
>
> OR is my -28V's so abnormal that I need to be looking at other issues
> in my rectifier pack to bring this negative voltage back into spec ???
>
> Could the negative voltage I'm getting be responsible for damaging this chip
> ???
>
> I have 2 new chips coming from Mouser. I'm not installing them until I'm
> satisfied that I've checked and double checked EVERYTHING involved.
>
> Thanks again and happy holidays to the group:
>
> 72 Jerry N0JRN
> ----- Original Message -----
> From: "Don Wilhelm" <[hidden email]>
> To: "n0jrn" <[hidden email]>
> Sent: Monday, December 14, 2009 6:22 AM
> Subject: Re: [Elecraft] KPA100 problem
>
>
>
>> Jerry,
>>
>> I will take back what I said about U4 - it is faulty.
>> That negative voltage is there only to allow the RS-232 drivers to produce
>> a negative level, the current draw should be minimal.
>> The only thing U4 does is convert RS-232 levels to TTL levels and
>> vice-versa.
>>
>> Actually -28 volts is a bit much and does exceed the maximum speced
>> voltage for the chip. -12 volts is more than sufficient and even -5
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.716 / Virus Database: 270.14.107/2564 - Release Date: 12/14/09 02:37:00
>
>

Andrew UK

Re: KPA100 problem

Hi Jerry,

I did not try to isolate as the track went straight to the max chip pin 8, I just removed the chip. C38 was the cap that was cracked, so instead of 10nF it was a few 100 pF!!! Or less.

I bought my KP100 some 3 years ago, and since then it has undergone a lot of improvement from Elecraft, if yours is less than a year old then you will have the latest revision. There are changes to the TR and switching and bias circuits.

I had around 150V to 200V at times, if pin 8 is low, then check the components to the right of C37. The high voltage supply is only bias and supplies very low current. Check Q6 as if this has a very small leak, it will drag the bias voltage down and check D11 to 14.

Q6 has failed a few times in my rig prior to the modifications, however, this was due to me leaving the aerial connected when high winds and storms were about.

73's

Andrew

Don Wilhelm-4 wrote

Jerry,

That answer depends on which set of "specifications" you want to believe.

I am saying that the Absolute Maximum Specification for the Maxim
MAX1406 for Vss (pin 8) is -14 volts - you can check the data sheet for
yourself. Yes, many KPA100s exceed that value - note that the KPA100 DC
voltage chart lists the nominal voltage at U4 pin 8 at -22 volts.
Whether that is a cause for failure of the chip is reason for
speculation, there is not enough data to say yeah or nay. .
What I have offered is a way to reduce the Vss voltage to the MAX1406
without also reducing the bias voltage to the KPA100 T/R switch. That
involves removing D8, and D8 alone. The data sheet Electrical
Characteristics current for pin 8 (Iss) is typical 185 uA with a maximum
of 500 uA. for a Vss of -13.2 volts Minimum to -10.8 Maximum - that is
not a lot of current draw on that pin.

I am stating that a Vss (U4 pin 8) voltage less than -14 volts exceeds
the Absolute Maximum Voltage rating per the MAX1406 datasheet - nothing
more and nothing less.

73,
Don W3FPR

n0jrn wrote:
> Don:
>
> Just to clarify !
>
> The -28V's I'm seeing at pin 8 of U4 is measured without the IC installed.
>
> Lets say for the sake of conversation that I install a good MAX1406 and it
> draws on the rectifier circuit a minimal amount.
>
> Would / could that bring the -28V's back into specs for this chip???. ( I
> have to figure Wayne designed the circuit taking this draw into
> consideration )
>
> OR is my -28V's so abnormal that I need to be looking at other issues
> in my rectifier pack to bring this negative voltage back into spec ???
>
> Could the negative voltage I'm getting be responsible for damaging this chip
> ???
>
> I have 2 new chips coming from Mouser. I'm not installing them until I'm
> satisfied that I've checked and double checked EVERYTHING involved.
>
> Thanks again and happy holidays to the group:
>
> 72 Jerry N0JRN
> ----- Original Message -----
> From: "Don Wilhelm" <don@w3fpr.com>
> To: "n0jrn" <n0jrn@mchsi.com>
> Sent: Monday, December 14, 2009 6:22 AM
> Subject: Re: [Elecraft] KPA100 problem
>
>
>
>> Jerry,
>>
>> I will take back what I said about U4 - it is faulty.
>> That negative voltage is there only to allow the RS-232 drivers to produce
>> a negative level, the current draw should be minimal.
>> The only thing U4 does is convert RS-232 levels to TTL levels and
>> vice-versa.
>>
>> Actually -28 volts is a bit much and does exceed the maximum speced
>> voltage for the chip. -12 volts is more than sufficient and even -5
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft@mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.716 / Virus Database: 270.14.107/2564 - Release Date: 12/14/09 02:37:00
>
>
______________________________________________________________
Elecraft mailing list
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