Fluke 89IV repair

[sunfire]

Hello

I've been given a Fluke 89IV for spare parts and I'm trying to fix it. From what I was able to figure out the meter was subjected to some (brutal) repair before : the LCD support bracket had all the tabs broken and the guy used some sort of cyanoacrylate glue (Superglue or some variant) to glue the LCD bracket to the PCB. Of course the glue made a mess on the PCB and it is hard to remove without affecting the PCB traces. The input receptacle has also been replaced (not a very good soldering job too). However these are not the main problem, the guy also managed to rip an SMD component off the PCB (on the backside of the PCB, top right, near the LT1307, I encircled it with red color in the attached photo).

Can anyone help me to figure out what that component is and what I can replace it with ? From the picture it contains 3 digits, " 9 " at the beginning and " 3 " at the end, however I'm not able to figure out the middle digit (or character). The photo attached is not mine, I found it here on the forum and I only marked the missing SMD component.

Super thank you very much in advance.

[ElektronikLabor]

It's very hard to figure out.
This component is placed near the LT1307 which is an DC/DC-Converter. Also the component has an (1Meg?) resistor accross two pins ... maybe a transistor in a SOT353 package? 

[wguibas]

the component doesn't have a middle digit, it's just a 9 and 3, or more probable E and 6.



Datasheet of 1307 chip:
http://cds.linear.com/docs/en/datasheet/1307fa.pdf

Observation:
Left top pin on E6 shows continuity  to pins 5 & 6 on 1307 
Right top pin on E6 shows continuity to pin 3 on 1307
Bottom right on E6 is ground common to pin 4 on 1307

SHDN (Pin 3): Shutdown. Ground this pin to turn off
switcher. Must be tied to VIN (or higher voltage) to enable
switcher. Do not float the SHDN pin.

SW (Pin 5): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to keep EMI down.

VIN (Pin 6): Supply Pin. Must have 1µF ceramic bypass
capacitor right at the pin, connected directly to ground.

[ElektronikLabor]

Observation:
Left top pin on E6 shows continuity  to pins 5 & 6 on 1307 
Right top pin on E6 shows continuity to pin 3 on 1307
Bottom right on E6 is ground common to pin 4 on 1307

Nice

This Component is connected to ShutDown-Input  and Vin of the Regulator  Maybe a PMIC (Power managment IC)?
Maybe that device monitors the input voltage and shuts down the Regulator, if the input voltage is too low. The threshold is adjusted by the 1Meg resistor 
There are a lot of PMICs with that package (SOT353, TSSOP5, TSOP-5).
Is this regulator used for LED-Backlight?

[sunfire]

Very nice indeed ! ( Thank you wguibas ! )

The marking definitely looks like an " E6 ", not " 93 " as I thought originally (with or without a middle character or digit). Again, thank you wguibas, your picture says more than a thousand words 

The only SMD components I found with " E6 " marking are two low dropout voltage regulators (R1111N161A with output of 1.6v and RT9167-21CB with output of 2.1v), one voltage detector (RN5VD46AA) and an inverter (TC7SU04F or TC7SU04FU). The only SMD component which would fit on the PCB based on the wguibas' finding is the inverter. The inverter has the input pulled up to Vcc with that 1meg resistor and it's driving the shutdown pin of the LT1307 switcher.

My guess is that inverter is part of a protection circuit which kills the output voltage generated by the LT1307 if something doesn't work properly (the LT1307 has the shutdown pin active low and the input pin of the inverter is pulled up to Vcc). The pullup resistor value (1meg) seems a bit high to me but I guess that depends on the current handling capabilities of the thing which is driving the inverter.

I just bought a few inverters off fleebay from China, I don't mind waiting three weeks for them to arrive, after all the meter is waiting in my drawer for the last 7+ months for its turn on the operating table 

Once again thank you for the quick help, I will update the thread when the inverters arrive, in the meantime the meter will return to the drawer.

[ElektronikLabor]

The only SMD components I found with " E6 " marking are two low dropout voltage regulators (R1111N161A with output of 1.6v and RT9167-21CB with output of 2.1v), one voltage detector (RN5VD46AA) and an inverter (TC7SU04F or TC7SU04FU). The only SMD component which would fit on the PCB based on the wguibas' finding is the inverter. The inverter has the input pulled up to Vcc with that 1meg resistor and it's driving the shutdown pin of the LT1307 switcher.

The TC7SU04F is a hot candidate 

[wguibas]

I would agree that the tc7su04 fits the bill.   glad I could help.

[u184754]

Hola les escribo desde Argentina porque tengo un problema con un Fluke 87 iv. Por error lo alimente con una fuente que funcionaba mal y desde ese momento no encendio mas. Lo unico que le veo es que esta quemado el componente marcado con rojo en la foto adjunta (cerca del IC 1307). No se puede ver la caracteriztica del mismo. Alguien me podra decir que es. Muchas gracias

Hi, I am writing from Argentina because I have a problem with a Fluke 87 iv. By mistake I fed it with a source that worked badly and from that moment it did not light anymore. The only thing I see is that the component marked with red is burned in the attached photo (near IC 1307). You can not see the character of it. Someone can tell me what it is. Thank you

[ModemHead]

The component looks like an inductor. There is a color code on top but I'm not familiar with the convention. Maybe somebody else can comment on it.

[u184754]

Thank you very much for the reply. I pass them how to identify an inductance in case someone needs it
https://www.coilcraft.com/colrcode.cfm
If I'm not wrong this should be 390nH