Products > Test Equipment

Repairing Fluke 8845A/8846A Multimeters - Part identification

(1/2) > >>

Orting:
Newbie here with an issue identifying parts on a Fluke 8845A. Everyone knows Fluke is not helpful in this matter, so desperatley in need of assistance. Have worked for many years with analog equipment especially tubes, so repairing a DMM is somewhat new to me. The 8845A does work, but no display. The PT shorted and fried several parts in the +60v rail including the power for the display. The Display works when connected to a working 8845A as well. Currently have +12volts on the +60v rail. Looking at posts here, I have discovered another user with the same issue in 2017, but didn’t see the resolution to the issue. Would like to replace all smd’s in the general area (7 devices), but need to translate the codes to order from mouser.

Q5 TN4CW
Q6 SAw
Q7
CR1 A11 1 (or could be an I)
CR3 IL44U
VR1 8J j
VR2 N34

Please find attached a picture of the affect area and components.

Thanks in advance for help you guys can provide,

Eric

AVGresponding:
Not sure shotgunning all the parts will help, particularly. They are unlikely to all be dead. I'd focus on the V-reg (8J most likely) and the MLCC caps first; if you remove them, does the short disappear?

Orting:
Thanks for the reply. The picture is of a good board and not the unit in question. For my unit there is a little more here. I have robbed parts from another Fluke 8845A and need to replace them too. Pulling parts from one board to another is haphazard at best and can damage the parts beyond being useful. At least one was damaged this way. When the PT shorted it took out several components as well with holes in the parts. One cap burnt thru to the middle layer of the pcb, leaving carbon behind that had to be dug out of the board. Hence the need to identify the parts with a part number that can be ordered. Is there a guide for part identification?

I wouldn’t be this concerned, but the unit works. Relays function when pushing the display buttons and it can be shut down from the front panel. I even get relay indications when touching the leads together in continuity mode.

floobydust:
I found some doing a quick check, it helps to add the package when searching.

CR1 MMBD1501A  Low Leakage diode "A11"
CR3 BAT54S Dual Schottky Diode "IL44"
VR1 MMBZ5234B 6.2V Zener "8J" SOT-23
VR2 MMSZ5263 56V Zener "N3" SOD-123

Q2 Si4532A Dual Mosfet P-N 30V SOIC-8
Q5 TN2425 N-Channel Enhancement-Mode Vertical DMOS FET 250V "TN4C" SOT-89
Q6 BSS123 Mosfet N-ch SOT-23"SA"
Q7 MMBT3904 NPN BJT "1AM"

T1 PE-65728 Pulse Electronics AUI Transformer

U2, U6 NC7SZ14 TinyLogic UHS Inverter with Schmitt Trigger Input SOT-23-5 Onsemi
U3 not sure markings

edit:
The circuit looks like a discrete HV linear regulator. For 60VDC out?
Q7/R35 for current-limiting
Q5 series-pass transistor
I would measure the voltages on Q5 to see what is going on, I would expect it be a vulnerable part.

Orting:
You my friend are awesome!!!!!!!!! Now is this from your experience or is there something you researched to find the part numbers? I really appreciate your help, just would love to know how to find the numbers myself.

Thank you for your help!!!!

Eric

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod