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Anritsu MS2721B internal CF card missing
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brainstorm:
Alright, @AnalogRF, my bad.

I hope that the attached photo is much clearer. I annotated the "clean" outputs of the coils as Shariar did in his video with postits (for the "A", mine is "B" series). Here's Shariar's postits for reference:

https://www.eevblog.com/forum/testgear/anritsu-ms2721b-internal-cf-card-missing/?action=dlattach;attach=1096304

My intention was to supply some of the voltage rails on both sides of the coils, but I understand that the switching (MOSFET, or more specifically [LT1765](https://www.analog.com/media/en/technical-documentation/data-sheets/1765fd.pdf) side is not helpful and it looks like healthy switching anyway so not very informative overall.

Please ignore the 535mV figure, that's just the DC Vpp measurement, that's also confusing, sorry about that.

Also, the DC barrel jack has an input voltage range of 12-15V DC, that's why I was confused with your 12V rail... that's just V_SYS, also seen in some of the coil inputs.

In any case, at least 4 of those coils are off... do you think that's a product of the power sequencing/early boot or is some rail is cooked?

The 15-0V postits (2 of the coils) indicate that there is 15V (barrel jack input) present in one side and 0V on the other side.
analogRF:

--- Quote from: brainstorm on October 26, 2020, 01:13:53 pm ---Alright, @AnalogRF, my bad.

I hope that the attached photo is much clearer. I annotated the "clean" outputs of the coils as Shariar did in his video with postits (for the "A", mine is "B" series). Here's Shariar's postits for reference:

https://www.eevblog.com/forum/testgear/anritsu-ms2721b-internal-cf-card-missing/?action=dlattach;attach=1096304

My intention was to supply some of the voltage rails on both sides of the coils, but I understand that the switching (MOSFET, or more specifically [LT1765](https://www.analog.com/media/en/technical-documentation/data-sheets/1765fd.pdf) side is not helpful and it looks like healthy switching anyway so not very informative overall.

Please ignore the 535mV figure, that's just the DC Vpp measurement, that's also confusing, sorry about that.

Also, the DC barrel jack has an input voltage range of 12-15V DC, that's why I was confused with your 12V rail... that's just V_SYS, also seen in some of the coil inputs.

In any case, at least 4 of those coils are off... do you think that's a product of the power sequencing/early boot or is some rail is cooked?

The 15-0V postits (2 of the coils) indicate that there is 15V (barrel jack input) present in one side and 0V on the other side.

--- End quote ---

1-did you check all the "test points" (not just the coils) that are marked on the board with various voltages? there are a few test points outside the PSU section for 3.3V and 1.8V and I think a couple of others, too. Those must exist in order to boot.

2-do not inject power to the coils from outside! you can try to supply outside voltage if you desolder the coil first and then use a current limited supply and slowly increase the current limit to check but if there are several rails missing, this becomes tedious...

3-what do you mean by "15-0V" in those stickers?

4-why are there no negative voltages anywhere? I remember there were one or two negative rails in there.

5-those rails that are zero, did you check for any shorts in their outputs? or in their mosfet and diode?

usually it is unusual that 4 rails fail at the same time together but as I recall some rails were the primary for other rails, so if one fails, 1 or 2 others may fail as well. With the help of datasheets you should be able to trace each dc-dc converter to its source/primary.

6-w.r.t. your last question, I wish I could remember exactly how the rails behaved but as far as I remember those power rails under the hood
were present right after power on (maybe except for charging) but the 24V which is marked somewhere outside the shield (near the ribbon connector) will turn on much later. so I believe the voltages under the shield should be present during boot. Now if they are dead, it's either a short in their load or a defect in the dc-dc converter itself.
I would start by checking each dc-dc converter separately from its input to output by following their datasheet. I think some of them had shut down for over current protection and if you look at datasheet you can check if over current has happened

I will try to locate my pictures of the ms2721b which I had taken with voltages written on them. I cannot find them in my laptop so
they are probably on one of the ssd backups... but i remember it was similar to what Shahriar had shown but with a little more detail

brainstorm:
Thanks for the advice and pointers!

1- Yeah, 3V3, 5V0 and 1V8 are also present on silkscreen marked vias.
2- Not yet, I will poke at the SHDN (Shutdown) pins for the LT1765's and see if other ICs are keeping those deactivated (or if they are blown or inactive via some other legitimate means).
3- 15V on some of the pins, 0V on the rest... so you can take those as effectively 0V output I reckon, need to study the LT datasheet and see what's going on with those.
4- Good question! the -15V0A rail is not present (0V)... but I guessed that rail just comes later on when powering up RF deck(s)?
5- I checked all diodes with the multimeter and they seem fine, I will proceed checking the LT1765 and LT1377's and their surrounding components next.... if there was a short somewhere, I guess that this thing wouldn't just consume 350mA and there would be something getting hot?
6- I hope it's indeed an overcurrent condition from some of the passives because otherwise I'll have to see how the TI IC immediately on the back of the board (TI TY1543) monitors and controls all of the LT's on the power supply can... a bit of a rabbit hole there, I hope I can find the fault sooner than that :)
analogRF:

--- Quote from: brainstorm on October 27, 2020, 11:31:35 am ---Thanks for the advice and pointers!

1- Yeah, 3V3, 5V0 and 1V8 are also present on silkscreen marked vias.
2- Not yet, I will poke at the SHDN (Shutdown) pins for the LT1765's and see if other ICs are keeping those deactivated (or if they are blown or inactive via some other legitimate means).
3- 15V on some of the pins, 0V on the rest... so you can take those as effectively 0V output I reckon, need to study the LT datasheet and see what's going on with those.
4- Good question! the -15V0A rail is not present (0V)... but I guessed that rail just comes later on when powering up RF deck(s)?
5- I checked all diodes with the multimeter and they seem fine, I will proceed checking the LT1765 and LT1377's and their surrounding components next.... if there was a short somewhere, I guess that this thing wouldn't just consume 350mA and there would be something getting hot?
6- I hope it's indeed an overcurrent condition from some of the passives because otherwise I'll have to see how the TI IC immediately on the back of the board (TI TY1543) monitors and controls all of the LT's on the power supply can... a bit of a rabbit hole there, I hope I can find the fault sooner than that :)

--- End quote ---

2-monitor the on/off pins of LT1377(s) and LT1765(s) "during the boot" with oscilloscope to see if and when they are on line.
3-just measure the pin that goes to the big filter capacitor. I think those rails are OK
4-as I remember it, voltages under this shield were all present at the beginning. The voltage for RF deck that comes on much later is a 24V
5-....no, not necessarily. Simply check the resistance to ground at those power rails that read 0V to see what might be going on

try to power it on with the RF deck disconnected. In a normal unit, it will boot.

brainstorm:
Thanks @analogRF,

I re-checked the rails as you indicated (via the output cap instead of the coils), I hope it makes a bit more sense now, I've attached an updated post-it screenshot.

2- I monitored the two "unresponsive" rails on power-on but there's little difference in the S/S or SHDN pins (LT1377 and LT1765 respectively)... the input is just 0V while on the working rails it reads somewhere in between 1.9V and 3.7V, which seems to match the spec.
3- The two non-postit-labeled rails: upper -15V and lower unknown (since I cannot see any nearby silkscreen indicating expected voltage) are totally silent... but since both are driven by different buck/boost ICs, I find it weird that it's not driven by external signals? I mean, I find it unlikely that both rails have failed at the same time... sounds more like a power sequencing/firmware/other_ICs issue?
4- I would very much appreciate that image in your backups to know which voltages should be present :)
5- Both IC series seem to be on the Mega-Ohm ranges (and both "healthy" and non-working show similar values) according to my multimeter.


I have *everything* disconnected, it's just the bare board sitting on the desk with no screen/backlight circuit/tweeter or anything else.

I followed the SHDN traces for the LT1765 to see if having ~3.3V present there would "wake up" the IC, but no switching activity happens on the other pins... I'll brainstorm a bit on what to do next, but followup suggestions/thoughts and info are super welcome! Thanks for the attention and effort, this is fun :)
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