Are you testing the parts in-circuit? You need to at least disconnect one leg to check them reliably. I'd recommend replacing C85 and C82 regardless. There are others I'd suggest if that doesn't help.
I can look and see what parts I last ordered for these if you want. On Fri, Jul 3, 2020, 10:32 PM Eric LK <[email protected]> wrote: > Hi, > > About one year ago my two "good" M100 stopped working almost at the same > time. I haven't got any time to look into them yet, but I really miss > taking notes on a M100 so I'm trying to get them working again. > > The first one kind of works but the contrast is ridiculously low, and you > can only see anything if you look almost perpendicular to the screen with > contrast dial to the maximum. > > I had a look at the Service Manual, and find out the issue is probably > caused by Vee being at -2.4V instead of -5V. > The same service manual says to check D15, C85 and D14. > > That's where I'm starting to be out of my comfort zone... > My multimeter has a diode testing function, and I definitely get > suspicious reading of D14 and D15: > For D14 I get 0.1V in both directions (black lead on the cathode, or black > lead on the anode) and for D15 I read 0V in both directions too. > > On my second M100 (which has another issue but the contrast and Vee are > fine) I read respectively 0.5V and 1.4V for D14, and 0V and 1.5V for D15. > > I don't know how to check C85, but having recaped the second M100 a couple > years ago I have some spare left so I suppose I can just change it if > fixing D14 and D15 desn't work. > > At this point I think (tell me if I'm wrong :o) ) that the next step is > replacing D14 and D15, but I wasn't able to find the exact same reference > listed in the service manual. > Is there an unofficial list of available modern parts for the M100 > somewhere? > > Here are the closest things I have found so far. Could someone tell me if > they have a chance to work? (or recommend a known working alternative?) > > D14 is listed as "DIODE, SILICON, ZENER, RD5.1 EL1 (QDZ5R1EL1A)" and I > found some "Fairchild BZX79C5V1 5.1v Zener Diode" ( > https://www.ebay.com.au/itm/Fairchild-BZX79C5V1-5-1v-Zener-Diode-x-10-/164107867434 > ) > > D15 is listed as "DIODE, SILICON, 1S2076 (QDSS2076#B)" and I found > "1S2076A HIGH SPEED SWITCHING DIODE DO35" ( > https://www.ebay.com.au/itm/50pcs-1S2076A-HIGH-SPEED-SWITCHING-DIODE-DO35-/252644110156 > ) > > Thanks! > > Eric > > >
