Re: bad bottlecap transistors causing squiggly vectors?

Wow.  Thanks for the detailed explanation of the deflection amps, William (or do you go by Bill?).  I suppose I fall in to the "newbie" catagory you describe... I'm not an electronics tech, nor electrical engineer.  Worse still, I'm a mechanical engineer who has been dabbling in electronics for a while.  In any case, I appreciate you taking the time to write up that detailed description.  It serves as a good suppliment to the text in the WG19V2000 manual.  I've actually been studying the similarities and differences between the V2000 and G05 lately.

Since it was apparently my "squiggly" vector observation that sort of touched this whole thing off, I should provide a little more detailed information:

1) This relates specifically to the G05-802 which I'm working on for my BZ project.
2) It appears to have OEM current sense resistors (R620 & R720) i.e. there's no clear evidence of solder work there.
3) Before I did anything to it, it functioned with the bottom half of the image collapsed, and the vectors were NOT squiggly.
4) The culprit of the semi-collapsed image was confirmed to be the negative-side transistor on the Y-channel (Q609 I believe).  It was open.
5) I did not have any new 2N3792s on hand, so I replaced it with an old (but working) one I had left over from replacing all of the bottlecaps on a V2000 a few months ago.  This fixed the half-collapsed image, and the vectors were still NOT squiggly.
6) I then replaced all of the electrolytic caps, except for the main power filters (C100 & C101).  I did this to try fixing the persistent "fuzziness," "blurriness" or "out of focus" appearnce of the image.  Before powering it back on after the cap replacments, I also replaced all 4 bottlecaps (2x 2N3792 and 2x 2N3716) with the new ones that came with the kit I had bought from Bob Roberts.
7) When I powered it on, I had squggly vectors.  I don't have a photo, but it was worst on short vectors (letters) and less noticable on longer vectors.  The small text was essentially illegible.  I was worried that one of the caps was bad, or backwards, or shorted, or open.  However, I re-checked my work, and everything appeared in order.
8) I then decided to do what was easy to do (I'm lazy), and swap the 4 transistors back out.  So I removed the brand new transistors, and put back in all of the "old" transistors.  I'm not sure what brand the old and new were, but they were different.  I can look at them this evening and report back.  I did not do or change ANYTHING ELSE at this time.  Just unscrewed the xistors, and screwed in the old ones again.
9) Powered on, and the vectors were no longer squiggly.  Problem solved, and back to the focus issue...

I haven't done anything more, but I can swap the new ones back in one at a time, and take photos of the screen at each step to try to determine exactly when things go bad...  However, I am convinced that one or more of those transistors must be the source of the squiggliness.

[Note I am not intending to disparage Bob Roberts at all here.  The components are certainly new, and are certainly labled as 2N3792 & 2N3716.  I have been buying stuff from him for some time now, and will continue to do so.  Bob's been nothing but great to me.]

Darren

--- On Fri, 7/30/10, William Boucher <boucher@mnsi.net> wrote:

From: William Boucher <boucher@mnsi.net>
Subject: Re: VECTOR: bad bottlecap transistors causing squiggly vectors?
To: vectorlist@vectorlist.org
Date: Friday, July 30, 2010, 12:46 AM

Perhaps I should have been more specific.  I don't blindly replace transistors.  If the originals are good, I keep them.  (Too expensive)  If I find a bad one, I do replace them in pairs to make sure the tolerances are the same.  I don't profess to be an expert in electronics but think that you would like to have evenly matched parts.  I'm sure one vendors tolerances are different from another's.  In the description of the wavy lines I referred to, it is hard to determine where the problem lies.  The specific case I am referring to is for a Space Duel monitor I rebuilt.  The cabinet was a project I purchased as non working.  Rebuilt brick, (bad rectifier, fuse block bad and hacked wiring), AR board toasted, and monitor non-working.  After rebuilding the AR and brick and fixing the monitor, I could not be sure the if the problem was due to the monitor or the main board or something else.  I tried another monitor with a jumper harness and the "waves" were much less obvious but still there.  I don't recall the origin of those transistors on the better monitor.  I have also found that the replacement transistors seem to be less tolerant of   Perhaps it could have even been classified as jitters.  I didn't have time to troubleshoot further as I was on a time schedule and had to have it delivered in working in a matter of days.  I was lucky to get it done as it was due to the hacks on the monitor.

I only offered to test a theory I had as a means of contributing to the group.  I will still attempt to document my findings and then submit them here for further abuse/discussion.  I would also like to point out that I do remove and reinstall the original bottle caps if they are still good but 30+ years of heat, smoke, dirt and dust do take their toll on the heat sink compound and I am doing what I can to keep them running for another 30.  Who knows, maybe I'm doing something wrong and I'll find it out.  As far as buying in matched pairs, I don't know if the vendor I purchase from has "matched" sets.  I only purchase bulk quantities and hope that the tolerances are close enough as they came from the same batch.  You're right, I don't have a curve tracer.  Wouldn't know how to use one if I had one.

I still have access to that game and may go by and grab the monitor and test it with a different game.

I also recently found a monitor out of a bulk buy with transistor numbers I wasn't familiar with.  I will dig it out and see what they cross to.  I would be interested in seeing what somebody else was using to get a monitor working.  For all I know, they are direct crosses.  Just wasn't familiar with the part numbers.

Do you have  a source for matched transistors at a "reasonable" price?

Pat

Kevin Moore wrote: I think Generally speaking it's also a good idea to used matched pairs on your push pulls too. But since buying MP's are not always convenient, and not everyone has a curve tracer to try and match them.  I'd have to agree with Mark though. I doubt that would be your problem. They would/could cause other issues. For example, Walling on Tempest. 

I will see if there is any visible difference between original, and the 2 sets of replacements transistors after a rebuild.  My month of August is pretty booked up right now but I need to get some 6100s done so I will attempt to get this info posted.  I'll even take video if possible.  No guarantees.

Pat Danis

PJ wrote: I was looking over Darren Finck's post regarding issues with a G05-802 having amongst a number of things, squiggly vectors.  This tweaks my memory of the issues I had with an Amplifone that had a bad case of twisted distorted vectors on certain objects (see my starwars posts from last spring).  I also had a similar issue on a G05 with original transistors that I figured were getting tired, and once replaced, the issue went away.   The Amplifone in question had new transistor pairs on both channels.  Since the original transistor pairs were long replaced prior to my involvement with whatever transistor the previous owner had on hand (literally), I replaced them with the correct parts, and from evidently, the same batch that I used in the G05.   What I ended up with was when the drive from the game board was normal, and the gains on the deflection were set higher to fill the screen, the vectors were distorted, like the start and stop rates were bad.  Tweaking the drive from the game board  to a high level, and dropping the gains on the deflection board made the effect less evident.   I'm wondering if the 2N3716s and 2N3792s have changed or the specifications aren't what they once were.  Anyone else seen this?--------------------------------------------------------------------------- ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org ** Please direct other questions, comments, or problems to chris_at_westnet.com

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Received on Fri Jul 30 10:24:39 2010