Transistor Looking Device with G21 Marking

[ataradov]

Are you sure it was not a repair attempt before you? And someone just put random parts at some point. It is not clear from your pictures, but it looks like the soldering quality is different on the 32 parts.

There is no way to identify parts. The markings are mostly there for confirmation, not identification.

There is no need to replace it with the same manufacturer. It just does not make sense. This diode array does not do anything most of the time.

[bostonman]

Are you sure it was not a repair attempt before you? And someone just put random parts at some point. It is not clear from your pictures, but it looks like the soldering quality is different on the 32 parts.

You're correct, the 32 marked parts are in channel 2 and 3 (the bad channels) which have less than acceptable quality soldering. Also, there is an AD823 in both bad channels with the same soldering skills.

In hopes the Agilent hybrid chips aren't the fault, I measured random points comparing them to the good channels (1 and 4) and came across some voltage/resistance differences.

Long story short, it led me to the poorly soldered AD823. My conclusion is that someone found the same voltage differences, traced it to the same points, took a chance on the AD823 and G21 being the culprit instead of the obsolete hybrid, replaced them, didn't fix the problem, and sold the scope.

Seeing as the AD823 in both bad channels had bad soldering (and also hoping they were the culprit), I bought new ones and soldered them (in my opinion I did a much better job because I didn't have several solder balls like the other person).

At this point, I don't see any other components that were replaced because everything has good factory looking soldering. The only remaining component that has bad soldering and may have been replaced with the wrong one is the G21 with a sideways 32 whereas the good channels (1 and 4) have just G21 and nice soldering.

Sadly, after all my work, I need to make a decision on whether to gamble with buying hybrid chips. The only ones I found are on Ebay from China and I've been told to watch for counterfeit parts. After buying them, I may need to find someone who is better skilled than I at replacing them.

Currently all the channels work in high Z input mode, but I can't calibrate it because it aborts when it starts channel 2. I assume because I can't calibrate it, this explains why each channel has a different offset. Channel 1 and 4 work fine in 50ohm mode, but the signal collapses on channel 2 and 3 in 50ohm mode.

I'm fearing that I buy hybrid chips, pay to have them replaced, and channel 2 and 3 are complete useless because they are counterfeit (or just junk). At that point I'd need to pay to have the old ones resoldered onto the board. Unfortunately I haven't found any information on the hybrid pin signals to take measurements.

[ataradov]

Can you trace any controls for the 50 Ohm mode? If it is all internal to the hybrid, then the answer is obvious.

[bostonman]

50ohm mode is driving me crazy.

I have yet to see a 50ohm resistor (or any unmarked resistors that measure 50ohm). Also, from what I can tell, if you look at the photo I took of the G21 component in the circuit, you'll see the single pin side is connected to a capacitor that goes into the hybrid. I'm guessing this is the main path into the hybrid, and all the relays before control whether to connect 50ohms to ground or not.

When I measure this point in high Z, I get a signal, when I measure it in 50ohm mode, it vanishes; and I can't locate a relatively normal looking waveform at any point.

The only POSSIBLE component (other than the hybrid) that could create 50 ohms is an IC on the backside labeled V224NS with (what I assume) is the company name above it: NAIS. The datasheet (I found a Panasonic one) describes this as having resistance, but, for the part number, it's less than 50ohms whereas I'm measuring almost exactly 50ohms.

A thought on the HP discussion board is: because I can physically measure 50ohms at the BNC connector on the front panel, then maybe a calibration will solve the issue of not working in 50ohm mode and it's not the hybrid. If I attempt a calibration, channel 1 (the good channel) goes smoothly and completes, I get an "Acquisition failure in cable connections test" error when starting channel 2, it starts after clicking 'OK', it continues for about ten-seconds, Windows error about the Agilent AG5483x software aborting, the program aborts, and I need to reset the scope.

[ataradov]

50 Ohm termination is likely to be inside the hybrid.

At the same time, your relay placement makes no sense. Are you sue it is not across the capacitor to make AC/DC work?

Also, what is the source of your test waveform? Are you sure it is not just loaded with 50 Ohms and can't drive a load that high?

[bostonman]

Also, what is the source of your test waveform? Are you sure it is not just loaded with 50 Ohms and can't drive a load that high?

That's a good question. I'm taking one of the signals from the rear of the scope (calibration out I think), which, on a good channel, looks good in 50 ohm mode (a clock pulse). I'm trying to trace this signal on a good channel just to figure out the path; again, in hopes that it leads me to something other than the hybrid. Sadly the signal (as I mentioned) seems to vanish, or get so small, in 50ohm mode, it doesn't make sense that it would decrease enough that noise would be injected onto it as it travels through the circuit(s).

As you can see from the pictures, several relays exist on the input side, and the V224NS is on the back side. I included a picture with red circles. The two resistors on the right in ch3 and ch4 were replaced by me. I found a difference in voltage on these and hoped the resistors had open end caps. I needed the resistors in the "good" channel (ch4) to measure the unmarked resistor values; and why a good channel had the resistors changed. The two top channels (3 and 4) have the G21 removed - I removed these to measure a "good" one and a "bad" on the bench - these were noted in a previous post. The two ICs in circles are the AD823 I replaced in hopes they were bad causing the 50ohm mode issue.

The schematic I drew that shows a relay on the input was noted as a "simplified section" because I'm uncertain how it's connected, however, I know relays are directing the input signal. This schematic began because I was trying to locate the difference in voltages between the good and bad channels. As you can see from the pictures, the AD823 in 2 and 3 was changed by me. The print on them is darker than the original bright white printed part numbers you see in ch 1 and 4.

[ataradov]

If the working channels work with the 50 Ohm setting and the same source, then it it not the source issue.

Another thing to do is to actually enable 50 Ohms on the channel and measure the resistance with a multimeter. Do that on the working and broken channels.

[TurboTom]

Your "ominous" SC70 component can very well be an HSMP-389C HP/Avago RF switching PIN diode. The marking is listed to be G2 and I often found that not all letters / digits present on the casing are relevant, frequently production batches, locations or datecodes (or what the facility manager had for breakfast...) are encrypted in these additional symbols. If this diode is really shot (as it appears), I've got a bad feeling regarding the hybrid...

[bostonman]

Another thing to do is to actually enable 50 Ohms on the channel and measure the resistance with a multimeter. Do that on the working and broken channels.

I've done that and all the channels measure 50ohms to ground. This was done a few months ago and why the thought of: if 50ohms is present, then maybe all it needs is a calibration and the "broken" channels will start working again, however, as mentioned above, when calibration begins on ch2 (the broken channel), the system halts and closes.

Your "ominous" SC70 component can very well be an HSMP-389C HP/Avago RF switching PIN diode. The marking is listed to be G2 and I often found that not all letters / digits present on the casing are relevant, frequently production batches, locations or datecodes (or what the facility manager had for breakfast...) are encrypted in these additional symbols. If this diode is really shot (as it appears), I've got a bad feeling regarding the hybrid...

Thanks for the feedback.... and I think you're correct, the hybrids are the culprit. Going about what to do with them will be the next challenge.

[gamalot]

If you believe that it is a dual diodes in series like BAT54S, I have a photograph for you. 

https://docs.rs-online.com/d69d/0900766b813b5eb7.pdf

---

I'm sorry I saw you mentioned this device with G21 mark in your reply on another topic, I thought you haven't got the answer yet.

After I responded to you here, I noticed that TurboTom has given the correct answer.

[bostonman]

After I responded to you here, I noticed that TurboTom has given the correct answer.

He did provide an answer, and has been extremely helpful. I am quite confident this device is a BAT54S, however, I am reluctant to use this for two reasons.

Prior to the link you provided, I couldn't find a single company that produced a BAT54S with the marking of G21. Also, this is feeding (or getting fed, or both) by the Agilent hybrid chip. If for some reason this device isn't a BAT54S, and I use the wrong device, I may blow the hybrids which will destroy the scope.

The link you provided looks helpful, and it appears, according to the table on page 3, I have either a lead code 2 or C which are basically the same thing, only a different package which is a simple solution.

The only confusion: I didn't see what the '1' represents, much like I didn't see what 'H' represents on the device in your picture.

[gamalot]

The third character represents the 'date code'. It can be any letter or number or even other symbols. In fact, if you look for pictures of HSMP-3892, you will also find G2m, G2/, G2V, or G27 and so on.

[bostonman]

I saw the date code, but didn't see what '1' would represent; maybe January?

In any case, I think that PDF is extremely helpful and adds another layer of confidence to believing I can replace this with a BAT54S without damaging the hybrids (or any other components).

It does, however, deviate a bit from the initial belief (maybe from what I interpreted) that G21 is the entire marking representing the type of component.

Just to reiterate a bit on why I want to be absolutely sure and not doubting the input from many on here. This scope has a bad channel 2 and 3 (four channels total). After many hours of measuring, I narrowed down the difference in measurements between good and bad channels to an eight-pin amplifier and a G21 component, but they looked like they were already replaced (but the G21 had a sideways 32). For obvious reasons, it was just easier to replace the amplifier rather than trying to determine if it's bad; plus the soldering was poor.

My guess: a previous owner tried fixing the bad channels and discovered the same difference in measurements between good and bad channels as I. In hopes that it wasn't the hybrid (which was my hopes), they replaced the amplifier and the G21 component. Either the G21 (and amplifier) was really the culprit, and, as a result of using a G21 with a sideways 32 (which may be a totally different component) blew the hybrid. Or the hybrid was just blown and the person replaced the amplifier (that may have already been good) and a G21 but used the wrong component.

Both G21 components in the bad channels measured differently than a G21 from a good channel (both were removed from the circuit). The amplifiers were replaced with new ones (and a much better soldering job now).

Also, I gambled and purchased used hybrids. I managed to replace channel 2 and the channel seems to work. Now I've replaced the hybrid in channel 3, but, in doing so, blew off a resistor by accident with the hot air pencil (I used Kapton tape over the whole area but one component still blew off). I'm waiting on a DigiKey resistor order to replace the blown off resistor. For obvious reasons I'm reluctant to power the unit with a missing resistor to avoid damaging anything. After installing the new resistor, checking the areas again (I've already carefully measured the continuity of each pin on the hybrid to assure a good soldering connection), I'll power the unit. Assuming the channels work with the new hybrids (and my soldering job), all I'll need is to purchase some BAT54S (which I forgot to order with my resistor order).

[gamalot]

For me, it doesn't really matter what the date code is, I just need to know that it is not part of the device model.

HSMP-3892 is used in the AFE of Keysight (Agilent) DSOX2000/3000 series oscilloscopes. You can find it in some pictures in that famous very long topic:

G2d on page 39
G2/ on page 40, 42
G2Z on page 52, 56, 57
G2G on page 56

https://www.eevblog.com/forum/testgear/dsox2000-and-3000-series-licence-have-anyone-tried-to-hack-that-scope/

[TurboTom]

...

In any case, I think that PDF is extremely helpful and adds another layer of confidence to believing I can replace this with a BAT54S without damaging the hybrids (or any other components).

...

Sorry @bostonman , but I really don't understand your reasoning to install a BAT54S instead of the obviously correct HSMP-389C. Do you understand the difference between a Schottky and a PIN diode? The use of a PIN diode as a fast RF switch to short-circuit too strong signals to ground makes complete sense in this place while a Schottky diode with its 10pF+ of capacitance (in case of the BAT54S) will form a nice low pass and probably limits the scope's bandwidth to a hundred-and-something megahertz. BTW, the total capacitance of the HSMP-389 series is around 0.3pF while its RF resistance with a posistive bias applied is as low as 2.5 Ohms. That's why HPAK used this component as an actively switched RF limiter.

I've got the impression that you really didn't understand how the circuit is supposed to work. A schottky diode installed instead of the correct PIN diode may not directly harm the instrument, but it won't protect it in case of too high RF level at the input either.

You've got to be pretty self-confident to just ignore well-meant advise from other forum members that only try to help you to get your instrument going again. But maybe you just want to learn it the hard way... 

[bostonman]

I apologize….. I thought you were giving an alternate part number that was a BAT54S - like a OEM number.

I’ll read your message tomorrow (or sometime this weekend) and respond based on your input. My priority was responding now just to make sure I didn’t rub you (or others) the wrong way.

[bostonman]

I re-read the message and looked at the datasheet (again).

The mistake I made was focusing on the device being a BAT54S. When I looked at the datasheet the first time, the title of 'pin switch diode' didn't register with me.

Obviously as I looked at the configurations, looking at them being just diodes further had me focused on it being a BAT54S.

Thankfully you called me out on my ignorance thus allowing me to realize the mistake of ordering the wrong device I almost made.

It seems this device has been narrowed down to a BAT54S or the HSMP-389x, and, according to your message, I can toss out the BAT54S theory.

I looked for the HSMP, however, it's obsolete. The alternate part numbers include this one:

https://rocelec.widen.net/view/pdf/wkwnaj16jm/INFNS15694-1.pdf?t.download=true&u=5oefqw

I looked at both datasheets and the HSMP can handle 1A of forward current whereas the one in the link above can only handle 100mA. I'll look at the other alternate parts to see if the others are better.

[TurboTom]

@bostonman -
the BAR63-04W should be a perfect replacement for the HSMP-389c. Don't worry about maximum pulse current and the other DC ratings. Rather have a look at your own circuit that you posted some time ago:



Where should any substantial DC current be coming from?

C5 is only conductive for RF signals. The input of the hybrid via R3 won't supply any current worth mentioning. And the biasing networks R1/R2 and R4/R5 won't harm the diode either. The way the circuit is supposed to work is as follows: During normal operation, the hybrid biases the (double) diode to block by raising pin 18 to the supply voltage. This way, the input signal "sees" the diode only as a small capacitance to ground (some fraction of a picofarad).

If the hybrid senses the RF input signal to be strong enough to become potentially harmful, it lowers pin 18 voltage, thus causing a current to flow through the double PIN diode, reducing its RF impedance and shorting some or all of the RF to ground through C1 and C4. This way, the hybrid should be (more or less) protected.

If of course someone considers it a brilliant idea to connect the output of a multiple-watt RF PA to the input of the scope, the poor diode (and in consequence the hybrid as well) haven't got a chance and will let go of the magic smoke that made them tick... 

I hope this clarifies a little the working principle of the RF branch's input protection.

P.S.: Just noticed -- the schematic appears to be not quite accurate, the center terminal of the double diode is connected directly to pin 3 of the hybrid and the 100R resistor (R3) appears to be on the input side of the "active" circuitry. If a diode has failed catastrophically, I'ld also have a look at R3 and both caps C1 and C4. R3 should protect the diodes and also the hybrid's input fairly well from moderate overloads. If the diode got destroyed anyway, someone must have fed an RF signal into the scope strong enough to arc over a vaporized resistor...

[bostonman]

I'll look at whether I already fixed that resistor error on my schematic. Not a big deal, however, if I'm asking for help on this forum, I'll waste the time of others if I'm posting incorrectly drawn schematics. Also, it brings down my credibility if I'm posting inaccurate stuff.

As you can imagine, I spent many hours tracing just to get that small schematic. I feel lucky to get the amount traced that I did. I'll admit, the schematic didn't make much sense and questioned my tracing, but I also didn't know anything about the hybrid.

Prior to buying the scope from someone, I was told about the broken channel 2 and 3, and if a voltage exceeds a certain DC voltage (some reason 5v comes to mind) is on the input while in 50ohm mode, the channel will blow up. At that point I was deathly scared of damaging the two good channels.

Unfortunately I'll never know how channel 2 and 3 got damaged. Upon hearing about blowing up the channels due to high signals, I assumed they were sensitive and poorly designed. Seeing that the G21 in those two broken channels had a sideways 32, measured differently out of circuit, and that a G21 can vary in part type across different manufactures, I wonder if someone injected a high powered signal, blew up the original G21, replaced it with the wrong type, and blew up the hybrid as a result.

You seem to have extensive knowledge about the hybrid functions. I searched for some theory of operations, or any information on the hybrids, but never found anything.

I believe my Digikey order is arriving today. Although I used Kapton tape to hold the components while using the hot air pencil, it managed to blow off a 1k resistor when I was replacing the hybrid in channel 3. I'm uncertain if I'll install the 1k resistor today or tomorrow, but, at after that, the scope will just need the new BAR63 in channels 2-4. Although I've powered it without these installed already, maybe I'll hold off until I get the BAR63s and install them.

Do you happen to know what the other digits in the part number represent in: BAR6304E6327HTSA1

The datasheet only seems to explain the BAR6304 part, but I don't know what the E6327HTSA1 mean. Digikey has more digits after, however, it's just tape and reel, cut tape, etc...

Most likely I don't need to worry about those numbers, but thought to ask just so I can know what I'm ordering.

[gamalot]

BAR6304 is the model number

E6327 are packaging suffixes

https://forum.digikey.com/uploads/short-url/2voJtGPwjujFVCBMZiIZH5oOb3d.pdf

HTSA1 are OPN (Orderable part Number) suffixes

https://media.digikey.com/pdf/Other%20Related%20Documents/Infineon%20Other%20Doc/Part_Number_Guide_Web.pdf

[TurboTom]

I don't know much about the hybrid in particular, but just by looking at the components around and the interconnection, my educated guess would be:

- It's a summing amplifier that combines the AC and DC branches of the single-ended input circuitry.
- It contains an RF detector circuit to limit RF input level via the double PIN diode in order to protect the sensitive RF input.
- Looking at the three differential pair output lines, it probably contains individual differential Drivers for the ADCs and probably for the trigger circuitry.

Once again, I'm not in any way an expert for these scopes, I even haven't got a HPAK scope, but with a little experience it's not that difficult to get an idea of what's going on in there.

I recommend to get exactly this diode: https://www.digikey.com/en/products/detail/infineon-technologies/BAR6304WH6327XTSA1/12686013

The "W" type is the one you want, it's an SOT-323 enclosure that's smaller than standard SOT-23 and it will exactly fit the footprint  on the PCB. Moreover, the smaller casing has lower parasitic capacitances / inductances. Don't get the "E" version!

[gamalot]

I don't know much about the hybrid in particular, but just by looking at the components around and the interconnection, my educated guess would be:

- It's a summing amplifier that combines the AC and DC branches of the single-ended input circuitry.
- It contains an RF detector circuit to limit RF input level via the double PIN diode in order to protect the sensitive RF input.
- Looking at the three differential pair output lines, it probably contains individual differential Drivers for the ADCs and probably for the trigger circuitry.

Once again, I'm not in any way an expert for these scopes, I even haven't got a HPAK scope, but with a little experience it's not that difficult to get an idea of what's going on in there.

I recommend to get exactly this diode: https://www.digikey.com/en/products/detail/infineon-technologies/BAR6304WH6327XTSA1/12686013

The "W" type is the one you want, it's an SOT-323 enclosure that's smaller than standard SOT-23 and it will exactly fit the footprint  on the PCB. Moreover, the smaller casing has lower parasitic capacitances / inductances. Don't get the "E" version!

I have not noticed their size, yes you are right, they should be SOT323 package. If the OP doesn’t mind buying components from China and knows how to buy them on Taobao, HSMP-389C is still available.

[bostonman]

Buying from China probably isn't a good idea since ideal substitutions exist; unless others think differently.

Unfortunately I no choice but to purchase the hybrids from China. They came soldered to a PCB that was cut from a larger board. I'm guessing (and hoping), the person or company cuts them from old HP equipment and they are truly Agilent chips and not knock offs.

I'll know within a week or so if those hybrids are good as I'll order these BAR components tonight and have them soldered when they arrive. At that point I can then power the scope and run some tests.

As for the SO23 versus SO323, looking at my case dimensions (see attached), neither of these are the same size (assuming I measured my component accurately), and the SO23 looked closer to the actual size. This doesn't mean the PCB footprint wouldn't support the SO323 or I couldn't make it fit on the existing footprint.

As it was pointed out, seems electrical advantages exist using the smaller package as parasitic capacitance/inductance is lower, so I should try making the SO323 work regardless.

[TurboTom]

What about sending one of the broken hybrids - after you pulled them from the scope - to @Noopy, our resident decapping king? He's a real wizard at taking superb quality micro photographs of the internals and this way, some knowledge could possibly be gained about the way these circuits work in detail! By doing so, you could return some of the favors you got in forms of consultation back to the forum  .

Btw, the components in the shape of an SOT-23 are only available in two sizes, SOT-23 (small) and SOT-323 (very small). If you look at your own photo of the concerning area of the PCB, you will find a semiconductor in a SOT-23 casing right below the "NAIS" relay. And that appears big in contrast to the double PIN diode, which, consequently has to be in an SOT-323 enclosure. Don't worry about taking measurements, the "W" version of the BAR6304 diode will fit the footprint on the PCB perfectly well.

[bostonman]

That's interesting, I didn't know someone on here decaps chips.

It's a good idea, however, these chips work for the most part, just (maybe) not in 50ohm mode; more when I get the scope tested. Either way, I'll keep this in mind and contact him should I want to sacrifice a chip.

I just placed another Digikey order, this time for 15 of the BAR64W. Although I don't have any intentions of using these, I also bought 15 of the E version and 10 of the BAT54S.

One thing about Digikey: you pay $4.99 shipping costs for a box the size of an encyclopedia, and it contains enough components that can balance on the head of a pen. I might as well just dump a few extra components on the order just for my inventory.