[cctalk] Re: FW: Re: ADM3a screen rot.
On 2024/01/29 12:45 p.m., William Sudbrink via cctalk wrote: Sellam Abraham wrote: I think you were fine. That's how you discharge them anyway. You were just missing the grounding wire :) Yes, I have one set up for just that purpose. Wire clamped to the shaft with an alligator at the other end. But I was so pissed off, I just grabbed a screwdriver off of my workbench. I'd rather not be the electron sink In this case. I've never taken a hit off of a CRT have you? Bill S. I had a chat with an electrical engineer about discharging old picture tubes many years ago, and he highly recommended using a suitable resistor array - like a HV probe to drain the charge on B&W monitors. Particularly ones that had a separate HV diode. He told me that discharging with a screwdriver can pass too much current (caused by a cascade of charges) through the diode array and damage them. This explained a problem we were having with B&W XY monitors made by Electrohome and Wells Gardner where the diode that was mounted between the HV transformer and the picture tube would fail and run hot, over heating the silicon rubber caps on the ends. I've not lost any HV diodes on machines since using our HV probe to discharge since that time. John :-#)# -- John's Jukes Ltd. 7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 Call (604)872-5757 (Pinballs, Jukes, Video Games) flippers.com "Old pinballers never die, they just flip out"
[cctalk] Re: FW: Re: ADM3a screen rot.
On 29/01/2024 20:45, William Sudbrink via cctalk wrote: Sellam Abraham wrote: I think you were fine. That's how you discharge them anyway. You were just missing the grounding wire :) I'd rather not be the electron sink In this case. I've never taken a hit off of a CRT have you? Yes, from a 26" CRT in a colour TV. It threw me across the room and taught me a lesson I'll not forget. BTW, if anyone has CRTs lying out of circuit, don't assume they're safe either. The EHT in normal use forces electrons into the glass, and when disconnected they very slowly migrate back to the aquadag, producing a substantial voltage. I remember seeing this demonstrated on an electronics course several decades ago. Which is where I /should/ have learned about discharging CRTs *through a suitable resistor* :-) -- Pete Pete Turnbull
[cctalk] Re: FW: Re: ADM3a screen rot.
Sellam Abraham wrote: > I think you were fine. That's how you discharge them anyway. You were just > missing the grounding wire :) Yes, I have one set up for just that purpose. Wire clamped to the shaft with an alligator at the other end. But I was so pissed off, I just grabbed a screwdriver off of my workbench. I'd rather not be the electron sink In this case. I've never taken a hit off of a CRT have you? Bill S. -- This email has been checked for viruses by Avast antivirus software. www.avast.com
[cctalk] Re: FW: Re: ADM3a screen rot.
> On 01/29/2024 2:00 PM CST Sellam Abraham via cctalk > wrote: > > > On Mon, Jan 29, 2024 at 9:55 AM William Sudbrink via cctalk < > cctalk@classiccmp.org> wrote: > > dripping. Anyway, like Wile E Coyote, after I had shoved a screwdriver > > under the uncooperative anode cap and finally gotten it off, I suddenly > > thought "What the HE** did I just do???". > > Bill S. > > I think you were fine. That's how you discharge them anyway. You were > just missing the grounding wire :) > > Sellam > Perhaps we should edit that? You were just the grounding wire :) Will Grownups never understand anything by themselves and it is tiresome for children to be always and forever explaining things to them, Antoine de Saint-Exupery in The Little Prince
[cctalk] Re: FW: Re: ADM3a screen rot.
On Mon, Jan 29, 2024 at 9:55 AM William Sudbrink via cctalk < cctalk@classiccmp.org> wrote: > There are several YT videos as you mentioned. Definitive is in the eye of > the beholder, I think. In hindsight, I would remind people to keep their > cool and carefully think through the safety procedures related to CRTs > before starting any work. I totally forgot to discharge my CRT but I got > away with it (I guess because it had not been powered on for four months). > An interesting side note is that the anode cap on the leaking CRT had gone > rock hard and there was a small "streak" on the back of the CRT that looked > like the plastic that it was made of had released some sort of oil. Maybe > it was attacked by something outgassing from the goo that the CRT was > dripping. Anyway, like Wile E Coyote, after I had shoved a screwdriver > under the uncooperative anode cap and finally gotten it off, I suddenly > thought "What the HE** did I just do???". > > Bill S. > I think you were fine. That's how you discharge them anyway. You were just missing the grounding wire :) Sellam -Original Message- > From: Bill Degnan via cctalk [mailto:cctalk@classiccmp.org] > Sent: Monday, January 29, 2024 12:16 PM > To: General Discussion: On-Topic and Off-Topic Posts < > cctalk@classiccmp.org> > Cc: Bill Degnan > Subject: [cctalk] Re: ADM3a screen rot. > > Is there a definitive guide for repairing screen rot. One of mine needs > it. I have watched others but I have not attempted my own. I might try > this at the Kennett Classic workshop this upcoming Feb 17th Bill > > On Mon, Jan 29, 2024 at 11:41 AM William Sudbrink via cctalk < > cctalk@classiccmp.org> wrote: > > > A quick note on ADM3a screen rot... my vintage collection resides in a > > cool > > (60-72 degrees F) dry basement. My "pride and joy" ADM3a (I have > > several) was just starting to show a few bubbles at the corners last > > September. I was pulling out some parts units on Friday and noticed > > that one had a much better screen than I remembered. Thinking that I > > might swap screens, I took a close look at "PnJ" and discovered to my > > horror that most of the lower half of the screen had "melted". "PnJ" > > was on a shelf, below eye level, nowhere near a vent or other source > > of heat. I was so annoyed that I immediately started cleaning/repair > > without taking any pictures (sorry). > > Fortunately, there does not appear to be any corrosion from the "goo". > > I completely desoldered and removed the keyboard assembly to get all > > of the crud out of (and out from under) it. The mainboard is a fully > > socketed example and the crud is down in several of the sockets. I'm > > still working on that. Anyway, the take away is don't assume (like I > > did) that the ruined ADM3as you see are the result of temperature > > extremes. It can happen anywhere. Keep a close eye on yours if you > > have one. > > > > > > > > Bill S. > > > > > > > > -- > > This email has been checked for viruses by Avast antivirus software. > > www.avast.com > > > > > -- > This email has been checked for viruses by Avast antivirus software. > www.avast.com >
