Topics

AVANTEK Amplifier Module


DougF VK4OE
 

Greetings to all readers!

I am wondering please if someone reading this message has practical experience with the internal construction and circuitry of AVANTEK microwave amplifier modules such as the one whose picture I am attaching to this message.

Following an eBay transaction four weeks ago, an AVANTEK 3A80-1782 amplifier module arrived in the mail this week.  Some scant technical information about it showing that it had been tested satisfactorily at an earlier time was supplied, but it is not exhaustive information.  Briefly, this amplifier is labeled for use over the 12 to 18 GHz range and the information supplied with it indicated that I should expect to get +15 dBm output power. It is 3¼" long by 1¼" wide and the label says +12VDC.

Before testing it, I mounted it on a heat sink, which had been recommended.  That done, the simple initial test was to discover that it was drawing 270 mA at +12V which seemed about right.

Next, I introduced an input signal on 14 GHz at -10 dBm and that produced an output power of about +15 dBm, after which I quickly found that it would deliver close to +17 dBm saturated output power from about -6 dBm input.  Both of those measurements seemed about right for such a module.  I recorded similar good results at 15 GHz and 16 GHz.

At that point I became distracted for a couple of minutes by something outside the "shack" and when I returned the output power meter was showing nothing and the current being drawn was now only 2 mA.  I was, of course, surprised and disappointed, particularly in that I wasn't, in my view, pushing it hard.

Removing and reinstating the DC supply has not restored things, neither has waiting several minutes.  It still draws only 2 mA.

Question 1:  Do you know or have some insight into the mode of failure that may have occurred here, and a possible way to fix it?

Question 2:  Having removed the heat sink and removed the eight screws holding the back plate of the module, the back plate does not want to "let go".  It appears to be firmly attached to something under the 'output' end of the amplifier module, but there are no more screws to remove.  Is someone on this list familiar with the way such amplifier modules are constructed internally, and who could give me some advice please?

Question 3:  Should I just regard the module as a 'write off'' and don't wast time trying to repair it?

What do folk think?

Cheers and 73,

--Doug Friend, VK4OE.

p.s.  I have already posted a similar message on the W1MBA microwave reflector but no-one with the experience I'm describing has emerged.  Apologies to those who have read a similar message there.....


Robin Szemeti - G1YFG
 

If I had to guess, I would say the being driven hard has blown a resistor or inductor feeding the FET.   In my experience, when FET's fail, they tend to fail short circuit, so I think it more likely the higher current of being driven hard has popped a surface mount resistor or possibly an inductor.  I doubt the active device itself has failed, it will be almost certainly the simple DC circuitry feeding it.

You are probably going to be able to fix it, if you can get it open, I'd give it a go.



On Fri, 30 Oct 2020 at 03:47, DougF VK4OE <uwaves@...> wrote:

Greetings to all readers!

I am wondering please if someone reading this message has practical experience with the internal construction and circuitry of AVANTEK microwave amplifier modules such as the one whose picture I am attaching to this message.

Following an eBay transaction four weeks ago, an AVANTEK 3A80-1782 amplifier module arrived in the mail this week.  Some scant technical information about it showing that it had been tested satisfactorily at an earlier time was supplied, but it is not exhaustive information.  Briefly, this amplifier is labeled for use over the 12 to 18 GHz range and the information supplied with it indicated that I should expect to get +15 dBm output power. It is 3¼" long by 1¼" wide and the label says +12VDC.

Before testing it, I mounted it on a heat sink, which had been recommended.  That done, the simple initial test was to discover that it was drawing 270 mA at +12V which seemed about right.

Next, I introduced an input signal on 14 GHz at -10 dBm and that produced an output power of about +15 dBm, after which I quickly found that it would deliver close to +17 dBm saturated output power from about -6 dBm input.  Both of those measurements seemed about right for such a module.  I recorded similar good results at 15 GHz and 16 GHz.

At that point I became distracted for a couple of minutes by something outside the "shack" and when I returned the output power meter was showing nothing and the current being drawn was now only 2 mA.  I was, of course, surprised and disappointed, particularly in that I wasn't, in my view, pushing it hard.

Removing and reinstating the DC supply has not restored things, neither has waiting several minutes.  It still draws only 2 mA.

Question 1:  Do you know or have some insight into the mode of failure that may have occurred here, and a possible way to fix it?

Question 2:  Having removed the heat sink and removed the eight screws holding the back plate of the module, the back plate does not want to "let go".  It appears to be firmly attached to something under the 'output' end of the amplifier module, but there are no more screws to remove.  Is someone on this list familiar with the way such amplifier modules are constructed internally, and who could give me some advice please?

Question 3:  Should I just regard the module as a 'write off'' and don't wast time trying to repair it?

What do folk think?

Cheers and 73,

--Doug Friend, VK4OE.

p.s.  I have already posted a similar message on the W1MBA microwave reflector but no-one with the experience I'm describing has emerged.  Apologies to those who have read a similar message there.....


--
Robin Szemeti - G1YFG


Gordon REASON
 

Hi Doug ..... firstly  , assume nothing .

Accept what you know  ...... and what you do not know .

It looks a little aincient (?) , and I can't say that I've ever taken an avantek amp apart .........

You have to very carefully and gently , remove a lid/cover , to enable a visual , and then an electronic check .

A 15 dBm input , I would'nt expect , to cause any damage ...........

It's more likely that an intermittant DC connection would .

However , get the lid off , take a good long look , and come back to us ......... as I'm sure that we are all wanting to help .

On 30 October 2020 at 03:47 DougF VK4OE <uwaves@...> wrote:

Greetings to all readers!

I am wondering please if someone reading this message has practical experience with the internal construction and circuitry of AVANTEK microwave amplifier modules such as the one whose picture I am attaching to this message.

Following an eBay transaction four weeks ago, an AVANTEK 3A80-1782 amplifier module arrived in the mail this week.  Some scant technical information about it showing that it had been tested satisfactorily at an earlier time was supplied, but it is not exhaustive information.  Briefly, this amplifier is labeled for use over the 12 to 18 GHz range and the information supplied with it indicated that I should expect to get +15 dBm output power. It is 3¼" long by 1¼" wide and the label says +12VDC.

Before testing it, I mounted it on a heat sink, which had been recommended.  That done, the simple initial test was to discover that it was drawing 270 mA at +12V which seemed about right.

Next, I introduced an input signal on 14 GHz at -10 dBm and that produced an output power of about +15 dBm, after which I quickly found that it would deliver close to +17 dBm saturated output power from about -6 dBm input.  Both of those measurements seemed about right for such a module.  I recorded similar good results at 15 GHz and 16 GHz.

At that point I became distracted for a couple of minutes by something outside the "shack" and when I returned the output power meter was showing nothing and the current being drawn was now only 2 mA.  I was, of course, surprised and disappointed, particularly in that I wasn't, in my view, pushing it hard.

Removing and reinstating the DC supply has not restored things, neither has waiting several minutes.  It still draws only 2 mA.

Question 1:  Do you know or have some insight into the mode of failure that may have occurred here, and a possible way to fix it?

Question 2:  Having removed the heat sink and removed the eight screws holding the back plate of the module, the back plate does not want to "let go".  It appears to be firmly attached to something under the 'output' end of the amplifier module, but there are no more screws to remove.  Is someone on this list familiar with the way such amplifier modules are constructed internally, and who could give me some advice please?

Question 3:  Should I just regard the module as a 'write off'' and don't wast time trying to repair it?

What do folk think?

Cheers and 73,

--Doug Friend, VK4OE.

p.s.  I have already posted a similar message on the W1MBA microwave reflector but no-one with the experience I'm describing has emerged.  Apologies to those who have read a similar message there.....


 


 


Paul Randall G3NJV
 

Probably a rather obvious suggestion but does that label hide a screw or two?
Paul


DougF VK4OE
 

That's a good suggestion Paul, and I've struck before that method of tidying up manufactured things.  But in this case, having peeled back about half of the label, it certainly seems like there are no screws under it.

The more I look at it, it seems like the top plate may be held in place by a continuous spot welding process around its perimeter.  More careful and determined investigation will take place tomorrow....

Thanks and cheers, --Doug, '4OE.


On 30/10/2020 10:40 pm, Paul Randall G3NJV wrote:
Probably a rather obvious suggestion but does that label hide a screw or two?
Paul


Gordon REASON
 

It's a laser weldedlid then..................

You may have to VERY carefully , drill just , through the lid , a hole , offsett near one end , and use something to ease the lid off ..... ore better still , find someone to mill around the edge of the lid ..............

On 31 October 2020 at 12:05 DougF VK4OE <uwaves@...> wrote:

That's a good suggestion Paul, and I've struck before that method of tidying up manufactured things.  But in this case, having peeled back about half of the label, it certainly seems like there are no screws under it.

The more I look at it, it seems like the top plate may be held in place by a continuous spot welding process around its perimeter.  More careful and determined investigation will take place tomorrow....

Thanks and cheers, --Doug, '4OE.


On 30/10/2020 10:40 pm, Paul Randall G3NJV wrote:
Probably a rather obvious suggestion but does that label hide a screw or two?
Paul


 


 


Paul Evans W4/VP9KF
 

Yes, it could well be. I think they copied the Plessey process. Depending on the application, the box may be Titanium. However, you may find it is silver-loaded epoxy and somewhat easier to remove. Whatever it is, apply a gentle (non-Dyson!) vacuum while de-lidding to keep swarf out of the circuit. Using a home CNC machine is a possibility to mill the weld apart.....

--
73, Paul Evans G4BKI [VP9KF]


 

I have a 15W PA 3.7-4.2 GHz which had a (very neat) welded lid. I eventually decided it had to come off which proved to  be quicker and easier that I expected on the mill. In fact it had a conventional screwed down lid underneath, so no need to replace the top.
For the purposes of "anti-tamper" it sure beats a tiny plastic "Warranty void if broken" sticker over one of the screws!


Colin Ranson
 

Hi Ken,

 

I have two of those ‘beasties’ with a ‘welded’ lid but they are 25w., also marked 3.7 – 4.2GHz, no makers name. They both came out of ex-BT 19” rack mounts with 2 huge heatsinks, one for the PSU unit which provided +12v from -28v and the other for the amp – probably ran 24/7/365.

 

I also have a 15w 6.2GHz unit from the same stable.

 

I tried a milliwatt or so in from a sig genny and the amp got hot, so did a 25w 3.5GHz rated dummy load..... alas nothing to measure power with, from memory – a least two years ago – it pulled about 8 amps.

 

I may well get a friend to mill the lid off.

 

If you, or anyone,  have any info I would be grateful.

 

Best regards to all and looks like another enforced period in the shack coming !

 

Colin de G8LBS.

 

 

 

Sent from Mail for Windows 10

 

From: Ken G3YKI
Sent: 31 October 2020 14:35
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] AVANTEK Amplifier Module

 

I have a 15W PA 3.7-4.2 GHz which had a (very neat) welded lid. I eventually decided it had to come off which proved to  be quicker and easier that I expected on the mill. In fact it had a conventional screwed down lid underneath, so no need to replace the top.
For the purposes of "anti-tamper" it sure beats a tiny plastic "Warranty void if broken" sticker over one of the screws!

 


Gordon REASON
 

You need to know how the inside is milled , but I removed some lids by , using a drill bit with a stop on it , to prevent the drill bit going through and doing damage to internal circuitry .

A connector from a chocholate block connector works well .

Then you can drill the lid , untill you create a hole .

Then very carefully , insert a screwdriver , and apply pressure and a click will indicate that the lid seal has broken .

The weld does'nt go very deep ...........it's a weatherproof seal .

It's best of course , to know the internal milling , then you can drill the lid , with a 2.5 mm hole , tap it with a 3mm tap .

Insert a 3 mm screw , and that will lift the lid off , and that done the lid will probably peel off ....

And as Paul suggested , use a vaccumm to take any swarf away .

I used a scalpel , sometimes to scrape the aluminium  ? ,  flat , for rewelding .. saved hours avoiding milling flat ........still waiting for my medal .


On 31 October 2020 at 12:05 DougF VK4OE <uwaves@...> wrote:

That's a good suggestion Paul, and I've struck before that method of tidying up manufactured things.  But in this case, having peeled back about half of the label, it certainly seems like there are no screws under it.

The more I look at it, it seems like the top plate may be held in place by a continuous spot welding process around its perimeter.  More careful and determined investigation will take place tomorrow....

Thanks and cheers, --Doug, '4OE.


On 30/10/2020 10:40 pm, Paul Randall G3NJV wrote:
Probably a rather obvious suggestion but does that label hide a screw or two?
Paul


 


 


DougF VK4OE
 

Greetings to all readers, and thanks for the various suggestions received on this subject.

I thought that a little update is in order following some purpose-driven investigations which I have made on this amplifier module today.

Firstly, yes, the top cover was held in place by a continuous seam of aluminium welding around the perimeter.  It was easy with a vertical milling machine to carefully remove enough material (only 1.2 mm) in order to be able to see the horizontal dividing line between two metal components all the way around.  After that, the cover with its complicated fitted extensions down into the "microwave electronics space" (most likely structures which prevent spurious oscillations) could easily be lifted free.

One of the accompanying pictures shows the amount of glass-substrate microwave circuitry with all its wire bonding, which was revealed when the top cover was removed.  On initial inspection, nothing seemed glaringly wrong or out of place there.

Next, the bottom plate with all of its screws removed did "pop free" this time with less effort  than I had been using the other day, revealing that it had been some semi-hard silicone cavity filler material which had been preventing detachment of the plate.  A couple of days under less tension with the screws removed may have facilitated it 'letting go'.

As you'll see from the other attached picture, what the bottom plate had been covering is just the DC input componentry, with two DC feed-through-paths leading from this little 'alcove' to the microwave electronics on the top side.  As already mentioned, the carefully milled hole or space there is filled with some sort of semi-hard silicone filler material which may be able to be removed with care using a sharp blade.

Although I have not yet measured what's going on DC-wise there, it is quite possible that the small tantalum capacitor that's present has gone short circuit taking the series diode with it.  Wouldn't it be very nice if the failure that has occurred is as simple as that?!  But that doesn't explain the residual 2 or 3 mA of current....  If those DC feed components test good, then the fault is likely to be in the impossible-to-work-on microwave electronics, leading to the amplifier being 'written off' with the only benefit from having investigated is to reveal things about these modules which may help others at a later time.

It may be a couple more days before I get back to these investigations, so I thought this update may be of interest to numbers of readers of this thread.  At least my questions about internal construction of AVANTEK amplifier modules of this vintage have been answered.

Cheers and best wishes,

--Doug Friend, VK4OE.

On 02/11/2020 1:12 am, Gordon REASON via groups.io wrote:

You need to know how the inside is milled , but I removed some lids by , using a drill bit with a stop on it , to prevent the drill bit going through and doing damage to internal circuitry .

A connector from a chocholate block connector works well .

Then you can drill the lid , untill you create a hole .

Then very carefully , insert a screwdriver , and apply pressure and a click will indicate that the lid seal has broken .

The weld does'nt go very deep ...........it's a weatherproof seal .

It's best of course , to know the internal milling , then you can drill the lid , with a 2.5 mm hole , tap it with a 3mm tap .

Insert a 3 mm screw , and that will lift the lid off , and that done the lid will probably peel off ....

And as Paul suggested , use a vaccumm to take any swarf away .

I used a scalpel , sometimes to scrape the aluminium  ? ,  flat , for rewelding .. saved hours avoiding milling flat ........still waiting for my medal.


Gordon REASON
 

Well done Doug .........

It's a bit sad that there is some filler material ,,,,, thats most likely there to stop vibration of wires or components .

The 2 to 3 mA of current , is most likely a DC Regulator bias current to supply a positive 5 to 8 volt positive bias to the Fets  (?) .........

Tantalums , my pet hate .........

Once , again within my employed days , I had a similar thing but with a harder material , I took it to a chemical man , who put it into a jar , of liquid , which gently broke down the epoxy , and it fell away ...... so , have a word with you local chemist ?

On 03 November 2020 at 12:33 DougF VK4OE <uwaves@...> wrote:

Greetings to all readers, and thanks for the various suggestions received on this subject.

I thought that a little update is in order following some purpose-driven investigations which I have made on this amplifier module today.

Firstly, yes, the top cover was held in place by a continuous seam of aluminium welding around the perimeter.  It was easy with a vertical milling machine to carefully remove enough material (only 1.2 mm) in order to be able to see the horizontal dividing line between two metal components all the way around.  After that, the cover with its complicated fitted extensions down into the "microwave electronics space" (most likely structures which prevent spurious oscillations) could easily be lifted free.

One of the accompanying pictures shows the amount of glass-substrate microwave circuitry with all its wire bonding, which was revealed when the top cover was removed.  On initial inspection, nothing seemed glaringly wrong or out of place there.

Next, the bottom plate with all of its screws removed did "pop free" this time with less effort  than I had been using the other day, revealing that it had been some semi-hard silicone cavity filler material which had been preventing detachment of the plate.  A couple of days under less tension with the screws removed may have facilitated it 'letting go'.

As you'll see from the other attached picture, what the bottom plate had been covering is just the DC input componentry, with two DC feed-through-paths leading from this little 'alcove' to the microwave electronics on the top side.  As already mentioned, the carefully milled hole or space there is filled with some sort of semi-hard silicone filler material which may be able to be removed with care using a sharp blade.

Although I have not yet measured what's going on DC-wise there, it is quite possible that the small tantalum capacitor that's present has gone short circuit taking the series diode with it.  Wouldn't it be very nice if the failure that has occurred is as simple as that?!  But that doesn't explain the residual 2 or 3 mA of current....  If those DC feed components test good, then the fault is likely to be in the impossible-to-work-on microwave electronics, leading to the amplifier being 'written off' with the only benefit from having investigated is to reveal things about these modules which may help others at a later time.

It may be a couple more days before I get back to these investigations, so I thought this update may be of interest to numbers of readers of this thread.  At least my questions about internal construction of AVANTEK amplifier modules of this vintage have been answered.

Cheers and best wishes,

--Doug Friend, VK4OE.

On 02/11/2020 1:12 am, Gordon REASON via groups.io wrote:

You need to know how the inside is milled , but I removed some lids by , using a drill bit with a stop on it , to prevent the drill bit going through and doing damage to internal circuitry .

A connector from a chocholate block connector works well .

Then you can drill the lid , untill you create a hole .

Then very carefully , insert a screwdriver , and apply pressure and a click will indicate that the lid seal has broken .

The weld does'nt go very deep ...........it's a weatherproof seal .

It's best of course , to know the internal milling , then you can drill the lid , with a 2.5 mm hole , tap it with a 3mm tap .

Insert a 3 mm screw , and that will lift the lid off , and that done the lid will probably peel off ....

And as Paul suggested , use a vaccumm to take any swarf away .

I used a scalpel , sometimes to scrape the aluminium  ? ,  flat , for rewelding .. saved hours avoiding milling flat ........still waiting for my medal.


 


 


Gordon REASON
 

Hi Doug .........

just looked at the pictures !

Very similar to what I worked with on many occasions .

They are individual RF amplifier modules .

The fets would be class A , and each fet having its own source bias resistor .

The 7th one is a voltage regulator , which woulf provide a stable + bias of 5 to 8 volts .

The regulator is a normal three terminal regulator , in Chip IC form , with the two chip capacitors of 1uF minimum on the same but of ceramic substrate .

The dc supply, input ,  to the regulator will be via the feedthrough , seen in the hole .

The 8th module is a temperate compensation , PIN Diode module , and again the current fed via the Feedthrough .

My picture definition and eyes are'nt too good , but I cannot see anything out of order , which is good .

Normal faults , to be seen , are an rf overload , of the input FETs , characterised by a sooty Plasma deposit arount the input fets , seen more clearly with a microscope , one of those USB , PC microscopes would be usefull !

Overload of the Chip Voltage regulator , again  best seen with a microscope , a melting of the top surface of the chip .

A microscope visual , of each ceramic module , with a side angled light , where you may see a crack across the substrate ......... imagine that the track to the gate is broken , then no gate control of the Fet , so full Idss current flows ......

This , for your excess current flow , would be more likely to be one of the modules nearer to the output .

If you can see a crack through a track , running a smoothed needle across the crack , to smear the gold together can restore correct operation .


So , get a dmm with one lead to the metal of the amp, ground .

Take a needle probe from the positive of the Dmm .

Set to the lowest Ohms range .

with no DC supply to the amp !!! connect ground to the sma connector ?

With the needle probe , probe to end of the chip capacitor(s)  , on the 7th module  .

Two of the ends should be ground .........

Each of the other ends , one should be a low resistance , as you are reading to fet circuit resistance , so expect cica 10 ohms .

the other end , from dc input , but there may be a second regulator hidden in the black epoxy , should be a much higher resistance of  > 2000 ohms ............

if that reading is low , then thats where the problem is ?



On 03 November 2020 at 12:33 DougF VK4OE <uwaves@...> wrote:

Greetings to all readers, and thanks for the various suggestions received on this subject.

I thought that a little update is in order following some purpose-driven investigations which I have made on this amplifier module today.

Firstly, yes, the top cover was held in place by a continuous seam of aluminium welding around the perimeter.  It was easy with a vertical milling machine to carefully remove enough material (only 1.2 mm) in order to be able to see the horizontal dividing line between two metal components all the way around.  After that, the cover with its complicated fitted extensions down into the "microwave electronics space" (most likely structures which prevent spurious oscillations) could easily be lifted free.

One of the accompanying pictures shows the amount of glass-substrate microwave circuitry with all its wire bonding, which was revealed when the top cover was removed.  On initial inspection, nothing seemed glaringly wrong or out of place there.

Next, the bottom plate with all of its screws removed did "pop free" this time with less effort  than I had been using the other day, revealing that it had been some semi-hard silicone cavity filler material which had been preventing detachment of the plate.  A couple of days under less tension with the screws removed may have facilitated it 'letting go'.

As you'll see from the other attached picture, what the bottom plate had been covering is just the DC input componentry, with two DC feed-through-paths leading from this little 'alcove' to the microwave electronics on the top side.  As already mentioned, the carefully milled hole or space there is filled with some sort of semi-hard silicone filler material which may be able to be removed with care using a sharp blade.

Although I have not yet measured what's going on DC-wise there, it is quite possible that the small tantalum capacitor that's present has gone short circuit taking the series diode with it.  Wouldn't it be very nice if the failure that has occurred is as simple as that?!  But that doesn't explain the residual 2 or 3 mA of current....  If those DC feed components test good, then the fault is likely to be in the impossible-to-work-on microwave electronics, leading to the amplifier being 'written off' with the only benefit from having investigated is to reveal things about these modules which may help others at a later time.

It may be a couple more days before I get back to these investigations, so I thought this update may be of interest to numbers of readers of this thread.  At least my questions about internal construction of AVANTEK amplifier modules of this vintage have been answered.

Cheers and best wishes,

--Doug Friend, VK4OE.

On 02/11/2020 1:12 am, Gordon REASON via groups.io wrote:

You need to know how the inside is milled , but I removed some lids by , using a drill bit with a stop on it , to prevent the drill bit going through and doing damage to internal circuitry .

A connector from a chocholate block connector works well .

Then you can drill the lid , untill you create a hole .

Then very carefully , insert a screwdriver , and apply pressure and a click will indicate that the lid seal has broken .

The weld does'nt go very deep ...........it's a weatherproof seal .

It's best of course , to know the internal milling , then you can drill the lid , with a 2.5 mm hole , tap it with a 3mm tap .

Insert a 3 mm screw , and that will lift the lid off , and that done the lid will probably peel off ....

And as Paul suggested , use a vaccumm to take any swarf away .

I used a scalpel , sometimes to scrape the aluminium  ? ,  flat , for rewelding .. saved hours avoiding milling flat ........still waiting for my medal.