I hope this thread will be written to a blog post? Lots of good info here! -- Anders Nelson
+1 (517) 775-6129 www.erogear.com On Wed, Aug 14, 2019 at 10:25 AM Charles via cctalk <[email protected]> wrote: > Thanks. I believe you are right also :) > The expensive ceramic packages have hermetic seals, not so the plastic > (epoxy) packages used in commercial grade parts. > > There are some kind of failures that can be fixed by baking - but I don't > know if this is one of them (if the bond wire is soldered to the die it > might work). If it detached from the weld at the lead frame, no go. Anyway > there are over 100 chips on the ADM-3A board and I would be more worried > about damaging the others with heat. > I just paid 71 cents for another LS193 ;) > > Charles > WB3JOK/0 > > -----Original Message----- > From: Dave Wade > Sent: Wednesday, August 14, 2019 5:02 AM > To: 'Charles' ; 'General Discussion: On-Topic and Off-Topic Posts' > Subject: RE: ADM-3A question > > Charles, > > I believe that TTL chips suffer from failure or detachment of the bonding > wire that runs from the die to the interconnect pin, which would result in > a > floating pin as described.] > Not sure if environmental storage affects this as chips should be sealed... > > I have also recently seen it suggested that heating the chip up in an oven > could affect a temporary repair (sorry I can't find the reference now). > > Dave > G4UGM > > > -----Original Message----- > > From: cctalk <[email protected]> On Behalf Of Charles via > cctalk > > Sent: 14 August 2019 00:20 > > To: cctalk digest <[email protected]> > > Subject: Re: ADM-3A question > > > > After hanging vertically for 36 hrs in a hot upstairs room, more goop > seeped > > out from under the keyboard. It now works again. Whew. > > > > While running on the bench for burn-in testing, a cursor problem suddenly > > appeared... it would only move every other keystroke. With the technical > > description and schematic at hand, it wasn't hard to track down a 74LS193 > > up/down counter with a blown (floating) LSB output. Confirmed by manually > > toggling that bit and the cursor would move back and forth one position. > > Meanwhile I removed the bad chip and put in a DIP socket. Naturally my > TTL > > collection didn't have an 'LS193 so I'm waiting on that. So I have a 24 > line, 1 > > column terminal :) > > > > The monitor was occasionally intermittent (no display at all, no HV, +15 > and > > drive signals OK). It seemed to change with movement of the wiring > harness > > from the main board to the monitor, too. I reseated the edge connector on > its > > PCB and it seemed to be fixed - but then the VERTICAL deflection > collapsed > and > > tweaking the height adjustment caused increasing loss. The 100 ohm pot to > the > > base of the vertical output transistor had picked that moment to go open. > > Changed that out and readjusted everything - so far so good after another > hour > > of run time. > > > > This ADM-3A could have been unpowered (and in a storage area without > > climate > > control) for a very long time. I wonder if that contributed to the > failures I'm > > seeing... hope there aren't any more until I get to use it for a while on > my PDP- > > 8/A (or 11/23+). > > > > > > --- > > This email has been checked for viruses by Avast antivirus software. > > https://www.avast.com/antivirus > >
