Fluke 123 Scopemeter and battery replacement

[Flukav]

Dear experts,
Following the battery & backlight update schematics posted on page number 2, I emailed IKSOR.si, as original pictures were not available anymore. One may find a repository here https://www.dropbox.com/sh/f72c2dpbbcg73bx/AABx5-jHr30Isnmg9G7eDMcXa?dl=0.
So far I upgraded my unit with a LED strip, as the 20yo CCFL tube was dead. The boost converter used, a cheap eBay MT3608 module, switching at 1.2 MHz, is hooked on C561, the 150uF 5VCC supply. It generates a 12VDC feeding 3x3 SMD LED located in the original tube holder. Light is evenly spread across the screen, way brighter than before.
Upon disconnection of the CCFL,  a strong yet clean 614.5Hz shows up whenever bare leads are connected on input A or B.
I of course disconnected the boost module, the DC supply, but the very same noise appear. Connection of a 1MO resistor on the HV pins doesn't help.
Any help will be appreciated.

[sorenkir]

Hi,

For my Fluke 125, I have bought a VHBW "compatible" battery pack.
It is not very expensive : 22€ shipped, compared to the 120€ of the original part, but it is far from being compatible:
it powered the Fluke with its initial charge, but did not take charge.
The connector is not properly wired (yellow pin, Battery Ident, is not at the right position), and the battery pack itself is "optimized" for no charge: no thermistor and no identification resistor (820 ohm for NiMh battery)!.
At least, there is a thermal protection...



I have swapped pins on the connector, put a thermistor from an old BP120 I had, added a 820 ohm identification resistor, and now the thing is OK.




After a first full charge, it powered the Fluke for about 4h.
The manual says 6h. I will see if it is getting better after a few charge cycles...

Michel.

[cd85233]

Dear experts,
Following the battery & backlight update schematics posted on page number 2, I emailed IKSOR.si, as original pictures were not available anymore. One may find a repository here https://www.dropbox.com/sh/f72c2dpbbcg73bx/AABx5-jHr30Isnmg9G7eDMcXa?dl=0.
So far I upgraded my unit with a LED strip, as the 20yo CCFL tube was dead. The boost converter used, a cheap eBay MT3608 module, switching at 1.2 MHz, is hooked on C561, the 150uF 5VCC supply. It generates a 12VDC feeding 3x3 SMD LED located in the original tube holder. Light is evenly spread across the screen, way brighter than before.
Upon disconnection of the CCFL,  a strong yet clean 614.5Hz shows up whenever bare leads are connected on input A or B.
I of course disconnected the boost module, the DC supply, but the very same noise appear. Connection of a 1MO resistor on the HV pins doesn't help.
Any help will be appreciated.

Does the frequency change when you hit the dimmer? It's likely the PWM signal coming out to the low-side driver to dim. You can likely disconnect the low-side driver by removing N604 or the R604.

I actually used the low-side as a ground point and I can vary my dimming with it. I do see some interference with the backlight on high, but I am going to go back in and shield the lines.

 Also, did you remember to attach to metal plate back ontop of the board?

[dimani4]

Hey guys,

I'm looking for the parameters for thermal fuse and NTC thermistor of original FLUKE123 battery. Please someone tell me their parameters. Or at least tell me what is written on the front of the thermal fuse for 70 degrees; (TB02-RBB0?)



Thank you.

P.S. I opened a new topic here:https://www.eevblog.com/forum/testgear/build-battery-for-fluke-123-and-question-about-the-power-supply/msg4444534/#msg4444534

[sorenkir]

Hi,

I have checked my original photo : it is TB02-BB8D 70°C

Michel.

[dimani4]

Hey Michel,

Thank you very much.

Now the question about the NTC thermistor. As I understood the color code (which are identical to the resistor codes) begins from the bottom of the thermistor (from the legs) as shown here:https://www.farnell.com/datasheets/2792960.pdf (see page 2). There are 4 color bands from the bottom to the top: the top colour of the apex determines the tolerance of the resistance. So can you tell me please these colours from the bottom to the top?

Thank you very much.

[sorenkir]

Hi again,

I am not sure of the coulours on the photo. The one I have used measures 12kOhms at room temperature (20°C).
In another original BP120 I have, the colours are brown, black, orange, gold and it measures 10kOhms.

Michel.

[dimani4]

Michel.

One more thing about the thermal fuse. Can you tell me please what voltage/current is? Maybe it's written in the wires or somewhere in the front panel?



Thank you very much.

[maki]

I have a dam question: will Fluke 123 work without battery pack?
I’ve received it without battery pack, tried to power it with its original power supply – it won’t turn on.
Any advice is appreciated.

[mahi]

maki: Yes, the Fluke 120 series Scopemeters do work without a battery installed. Start by checking the power supply. According to the specifications the original PM8907 power supply is 15V / 300mA but mine reads about 20.4V without load (center pin negative).

[Uzunov]

Hello everyone! I recently got a fluke 123 and its battery is naturally dead. I'm thinking of replacing it with two lithium batteries as described in the topic, but I couldn't figure something out. When doing this conversion what resistor should be put to the battery sense pin!? Should it be 825 ohms or 0 or does that no longer matter. The device is one of the oldest and may not recognize a nimh battery.

The translation from Bulgarian was made with Google Translate and there may be inaccuracies.