Fluke 23, series 1, dead clock and OHMS/continuity ranges - Page 1
Forum section: electronics / repair

author: robert.rozee
author_rank: Frequent Contributor
timestamp: June 29, 2020, 08:00:16 pm
content: hi,i picked up a non-working fluke 23 (original) for $10 yesterday. it was completely unresponsive.turns out the crystal oscillator was not functioning, and nothing i could do - including swapping the crystal with a known good one - would fix this. in the end i pulled out the crystal and 2 capacitors, replacing them with a PCF8563 RTC that i happened to have a few of. the PCF8563 has a buffered 32khz output pin 7) that is active on powerup, and this with a 400k pullup did the trick - the 23 sprang into life. the extra current consumption (picked up off TP1) is around 10uA.now i see that the AC and DC volts ranges working, current measurement appears to work (on DC at least), but both OHMS and continuity are dead.on OHMS the meter ranges up to the top range and sits on OL, with subsequently shorting J1 and J4 having no effect. interestingly, however, is that if the meter is turned on and immediately to OHMS while keeping J1 and J4 shorted, thereafter the behaviour is quite different: it displays 0.0 ohms initially but the reading slowly increases. if the short between J1 and J4 is removed, the neter ranges up and then proceeds torapidlycycle through the ranges while flashing OL.i've checked out the resistor pack, R1, R2, Q1, Q2, switch contacts, etc. everything seems to be in order and am seeing the expected sorts of voltages everywhere. with the exception of when J1 and J4 are shorted there is still about 1.4 volts on the 'OHS' pin (pin 20 on U1) - shorting 'OHS' to J4 at this point has no effect on the behaviour of the meter.i'm picking someone poked a high voltage into it while set to OHMS, and that the 'OHS' pin has been fried. any suggestions for further diagnosis?btw, i'm working off a 23 series 2 schematic, as i couldn't find the 23 series 1 service manual online. does anyone have a copy of this?cheers,rob :-)

author: mzacharias
author_rank: Frequent Contributor
timestamp: June 30, 2020, 02:07:36 pm
content: re: schematic etc.The Fluke 77 Series 1 should be the same as the 23 (pretty sure but not 100%)So far as I know the 23 was the "industrial" version.Schematics etc should be readily available.

author: guswin95
author_rank: Contributor
timestamp: June 30, 2020, 03:45:43 pm
content: The manual is available at Fluke own website for download. Fluke series I include 77, 75, 73 and 70 and the yellow 23 and 21..BTW, Try reflowing the main chip even though it may appear fine.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 30, 2020, 08:47:10 pm
content: Fluke series I service manual athttp://bee.mif.pg.gda.pl/ciasteczkowypotwor/Fluke/70%20Series.pdfI agree with the reflow suggestion. It's been suggested before athttps://www.eevblog.com/forum/repair/fluke-21-series-ii-repair/https://www.eevblog.com/forum/repair/repair-fluke-77-series-i-gt-u1-really-dead/https://www.eevblog.com/forum/repair/fluke-27-well-at-least-the-dc-amps-ma-and-ua-works/https://www.eevblog.com/forum/testgear/fluke-77-strange-demise/https://www.eevblog.com/forum/testgear/fluke-77-strange-demise/msg503530/#msg503530

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 04, 2020, 03:04:57 pm
content: Quote from: retiredcaps on June 30, 2020, 08:47:10 pmjust tried reflowing U1, first pin-by-pin, then using hot air on the whole chip. alas, it made no difference to the behaviour, OHMS and diode/continuity are still both non-functional.the manual at bee.mif.pg.gda.pl seems to be the right one, my 23 matches the diagram on page 7-3/7-4 titled 75-1221. see attached image, also attached, image of the crystal 'replacement'.cheers,rob :-)