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Anritsu MS2721B internal CF card missing

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brainstorm:
Alright, almost one year later, I'm not giving up on this baby, this repair is gonna be EPIC if and when it works again: persistence is not futile, sunk costs do not exist in hobbies kind of thing ;)

Jokes aside, I now have access to a thermal camera, I'm attaching the photos... The detected components when powering up are clearly not shorting since the temperature is very reasonable (around 31degC tops) and the board is currently only drawing around 330mA according to my lab PSU. At least this information underlines the fact that since only that IC is "lightning up" on the camera, there's clearly something wrong with the power sequencing for the other chips? So I'll see how the other rails are brought up, please let me know if my logic is flawed...



That LT1765 IC and accompanying diode shown in the thermal picture are VR1001, as can be seen on a previous post picture: 

https://www.eevblog.com/forum/testgear/anritsu-ms2721b-internal-cf-card-missing/?action=dlattach;attach=1096280

Now, I was tracing SHDN (shutdown) signal from that IC, which is 3,3V at the moment, which means that it's active (inverted logic according to the datasheet?):

https://www.analog.com/en/products/lt1765.html

This rail seems to be operating fine, with an arguably clean, switching 14V on the output.

I'll now compare the shutdown signals for the other LT1765 ICs and rails, I'll keep you folks posted as I progress in this, troubleshooting ideas/hints welcome as always ;)

brainstorm:
I've now figured out the circuit/topology of VR1001 (one of the LT1765 regulators):



Which is slightly different from the topologies exposed in the official datasheet on quick peek:

https://www.analog.com/media/en/technical-documentation/data-sheets/1765fd.pdf

But anyhow, now I know that VR1000, VR1001 and VR1002 are all connected through the same SYNC signal... unfortunately I couldn't figure out where those SYNC signals are connected on a quick and dirty continuity "copper braid scan" across other neighboring components for both sides of the board:



Similarly, VR1004 and VR1003 are connected to each other via their SYNC signal, but do not share that one with the other VR group mentioned above... which might suggest two independent "blocks" of power regulators to sequence/turn on?

Question to @analogRF and others: any idea about which IC could be orchestrating those two sets of power rails?

brainstorm:
> No, I meant I think there were some more DCDC converters on the back of the board. I cannot remember exactly. I might be wrong

Hm, I can't remember any DCDC converter at the back of the board but will check... Right now I wonder which IC does the coordination between those DC converters inside the metal can so I can follow the power-up chain.

analogRF:

--- Quote from: brainstorm on October 02, 2021, 10:30:23 am ---> No, I meant I think there were some more DCDC converters on the back of the board. I cannot remember exactly. I might be wrong

Hm, I can't remember any DCDC converter at the back of the board but will check... Right now I wonder which IC does the coordination between those DC converters inside the metal can so I can follow the power-up chain.

--- End quote ---

this is all controlled directly by the CPU (or the FPGA). I dont think the issue is "power up chain", in fact i am pretty sure it isn't...if all converters are ok, then you should look somewhere else. can you put the unit in bootstrap mode? is there anything at all appear on screen when powered on? have you tried to telnet (very quickly after power on)? are you sure the CF card is ok and FW is Ok? there is a chance that during a FW upgrade someone screwed up. That can be solved by putting the unit in bootstrap mode..
if it is totally dead, then check the signals around the memories and CPU. are they showing any activity? dont waste too much time on chasing the power up chain...if the dc dc converters are ok, then power supply is working and problem is somewhere else really. right now I am working on a 2721B with tons of RF issues (bad attenuators + LO unlock) all are fixable easily but I can check some signals if you need...

EDIT: the bare minimum you need to have in order to see the unit powering up is 1.8V, 3.3V and the backlight voltage (i dont remember which supply line goes to backlight driver but you can figure it out easily) if those are all there then you can forget the power supply.

brainstorm:
Thanks for the response and the hints! I've checked the 1.8V, 3,3V and backlight voltage (seems to be same as VIN on a couple of pins of the connector, 14V and 3.3V on another two, GND on the rest). Unfortunately no, there's no telnet nor bootstrap mode possible, AFAICT :/

When the unit was "working" (boot sequence until "Application package: null" prompt), it did boot even without ANY CF card inserted. So I'm trying to trim down all possible external factors here and thus I just have the bare board which draws around 300mA at 14V at the moment on my desk... could you do the same experiment and let me know how much it draws? Disconnect *everything* (including backlight an display) and see how much it consumes and if it seems to boot by eyeing power consumption fluctuations (mine hovers around 300-350mA from power on)?

If I connect the display, no backlight appears, just a brief noticeable change of state from the LCD pixels. I see plenty of activity on the SH4, the flash chip's WAIT signal (btw, can you probe the E4050 and E4049 near those flash 256P30T IC's?) and the RAM ICs too (addresses latching and data coming in/out).

Reading this thread, my last hunch was about the Flash chips but I'm still uncertain :/ ... I guess that putting some logic analyzer probes on the SRAM and try to see where addresses are could help determine how many instructions are being fetched/executed by the SH4?... any other simpler checks I can run before that?

Thanks a ton in advance @analogRF!

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