Commodore 1084s-P1 CRT repair - Page 1
Forum section: electronics / general

author: djos
author_rank: Unknown
timestamp: September 29, 2017, 07:24:12 am
content: So I finally stopped procrastinating and started work on my Commodore 1084s-P1 CRT repair project. It should be fairly straight forward as the number 1 failure with these is the HOT going bang and taking the FlyBack transformer with it.Required parts:and this is as far as I got today before fatherly duties intervened:At least it's fully discharged and im ready to start desoldering al the relevant components.

author: djos
author_rank: Unknown
timestamp: September 30, 2017, 05:48:34 am
content: Finished off the HOT & FlyBack Transformer replacement today - just need to replace the power switch now as it doesnt stay on.Components gone:New ones in:putting the neck board back together:half done - J1 wire hasn't been soldered in yet:and mostly back together:and she works!Some adjustments will be required (pic is too bright) but i'll sort that after I replace the power switch in a few days (it's in transit).

author: SeanB
author_rank: Super Contributor
timestamp: September 30, 2017, 06:08:47 am
content: Check all high value resistors ( anything over 10k) in the high voltage side, they do tend to drift high, and this causes the excessive brightness. Also resolder R3514, to make sure any hidden dry joint there does not kill the new parts.

author: djos
author_rank: Unknown
timestamp: September 30, 2017, 06:21:27 am
content: Quote from: SeanB on September 30, 2017, 06:08:47 amI haven't adjusted the "screen" pot on the Flyback yet, out of the box it's usually set too high.Thanks for the tip, I'll definitely check the resistors and the solder on R3514. Can you reliably measure resistance in circuit?

author: vk6zgo
author_rank: Super Contributor
timestamp: September 30, 2017, 07:36:57 am
content: You are fixing a Monitor.The big glass thing is the CRTCalling the whole thing a "CRT" is an incredibly annoying species of "Computer person speak" which has no place in an electronics forum.

author: djos
author_rank: Unknown
timestamp: September 30, 2017, 07:54:11 am
content: Quote from: vk6zgo on September 30, 2017, 07:36:57 amLol, it's still using cathode ray tube technology, it's just a very highly developed distant cousin.

author: djos
author_rank: Unknown
timestamp: September 30, 2017, 07:57:22 am
content: Ok, I turned the "screen" pot down on the FBT and it's no longer over driving the screen.I just need to hook up a video source and finish tweaking.

author: djos
author_rank: Unknown
timestamp: September 30, 2017, 10:30:30 am
content: and now focused.I checked all the solder joints with my 5x illuminated glass and they all look fine - I couldnt even find R3514 on mine so it might be only on other models? (mine is the -P1)Mine's obviously been repaired once before as there are quite a few solder joints with non factory rosin around them that wasn't cleaned off with IPA.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 30, 2017, 12:07:48 pm
content: Quote from: djos on September 30, 2017, 07:54:11 amMy rant was a bit "tongue in cheek", but it does annoy me.The CRT is just one component of the equipment you are fixing, & the only component which utilises "cathode rays".All the other active devices are semiconductor based.Some people used to refer to cars as "motors", or transistor radios as "transistors".(& probably still do)It sounded silly then, & it does now when the same thing is done with Monitors.It can also be misleading to beginners.On another thread someone was getting all overwrought about the dangers of CRT tubes because they read on a "computer" website that there was some large amount of lead inside the "CRT".The website was, of course, referring to the whole Monitor, & including the amount of lead in the PCB & other soldered connections.

author: Bruce Abbott
author_rank: Frequent Contributor
timestamp: September 30, 2017, 07:03:15 pm
content: Quote from: vk6zgo on September 30, 2017, 12:07:48 pmCRT is short for 'CRT monitor' whichisthe whole thing. If you think acronyms have no place in an electronics forum then you can expect to continue being incredibly annoyed.

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2017, 07:23:40 pm
content: QuoteErr, CRT is short for Cathode Ray Tube, nothing more. It's a standalone component. It could be in a TV, a scope, spectum analyser, camera... or a monitorQuote from: vk6zgo on September 30, 2017, 12:07:48 pmCRTs in TVs and Colour monitors use leaded glass in the faceplates to minimise X-ray emission. You should be very careful not to store Port or Sherry in them for long periods (as is the advice for Lead glass decanters) for fear of Lead leaching.P.S. "CRT tube" is a tautology.

author: djos
author_rank: Unknown
timestamp: September 30, 2017, 09:19:23 pm
content: It's a silly argument, although I do get irritated by OEM's calling LCD tv's led tv's when only the backlight is led and the display itself uses an LCD panel.

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2017, 09:27:01 pm
content: Me too - they'd have been really screwed it they hadn't used Organic LEDs in OLED TVs.P.S. Yes, I agree - Just Saturday evening high spirits in my case. Don't worry, it's worn off now.P.P.S. We all know we should be talking about VDUs anyway.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 01, 2017, 08:07:03 am
content: Quote from: Gyro on September 30, 2017, 07:23:40 pmYes, but Cathode Ray Tubes are unlikely to have Port or Sherry stored in them.I don't usually store Port for very long at all!He actually linked to the website, & from context, & the mass quoted, it was definitely to do with the amount of solder in the monitor.QuoteYou got me there!I noticed I had done that, & considered doing battle with the iPad to edit it, then decided "To hell with it, let someone have some harmless fun!"

author: Bruce Abbott
author_rank: Frequent Contributor
timestamp: October 01, 2017, 08:25:08 am
content: Quote from: djos on September 30, 2017, 09:19:23 pmDefinition of:LED TVA flat panel LCD TV set that uses LEDs (light emitting diodes) for its backlight source rather than the earlier cold cathode fluorescent lamps (see CCFL). Smaller, more power efficient and having a greater optical range than the fluorescents, LED TVs produce deeper blacks and more saturated color. In 2005, Sony offered the first LED TV.Although an LED TV is really an LCD TV with LED backlighting,the industry branded them as LED TVs to avoid monikers such as "LED backlit TV" or "LED-based LCD TV.".

author: djos
author_rank: Unknown
timestamp: October 01, 2017, 09:12:14 am
content: Quote from: Bruce Abbott on October 01, 2017, 08:25:08 amI'm well aware of why, still doesnt change the fact that "LED TV's" are nothing of the sort, they are LCD TV's with an LED backlight - we didnt stop calling them LCD Screens when front lighting was first used, or when backlighting replaced front lighting.So in summary, "LED TV" = marketing BS.At least Plasma and OLED screens are accurately named.

author: djos
author_rank: Unknown
timestamp: October 09, 2017, 04:27:48 am
content: Replacement power switch finally arrived today after the courier company lost it and mysteriously delivered it to my mailbox 4 days after claiming to have delivered it too me in person (including me signing for it apparently). Amazing how responsive they can be when you accuse their driver of fraud!Unfortunately I'm of crook atm, so can't install it for a few days.

author: BubbaMc
author_rank: Contributor
timestamp: October 11, 2017, 07:38:01 am
content: Nice work.Is that the model with a live chassis?BTW feed it an RGB picture if you want to see how good it is

author: djos
author_rank: Unknown
timestamp: October 11, 2017, 07:53:17 am
content: Quote from: BubbaMc on October 11, 2017, 07:38:01 amCheers.Not sure what you mean by live chassis? The chassis is plastic so non-conductive.Yeah I'll be testing and focusing it properly, with an Amiga putting out RGB, once I've recovered from a nasty bout of gastro that the daughter brought home from school.

author: BubbaMc
author_rank: Contributor
timestamp: October 12, 2017, 01:24:13 am
content: Quote from: djos on October 11, 2017, 07:53:17 amSee here for a brief discussion:https://www.eevblog.com/forum/beginners/live-chassis/One of my later model 1084S monitors has a live chassis (assume Commodore did this as a cost saving measure), so I'm not willing to attempt repair until I get an isolation transformer.

author: djos
author_rank: Unknown
timestamp: October 12, 2017, 01:47:46 am
content: Quote from: BubbaMc on October 12, 2017, 01:24:13 amHmmm, I'd have to take a closer look at mine but seeing as it's a rebadged Philips Im not terribly concerned. The main danger with these is the FBT, if you dont discharge them properly before starting work on them you can end up with a paralysed arm and a nasty headache for a few hours. I recall being dismissive once back in the 90's while working on a 21" Trinitron, the jolt I got that day corrected that dismissiveness permanently and so now i'm paranoid instead!EDIT: there's grounding wires between all the boards and there's no live chassis that I can see - imo it's a pretty nice design.

author: helius
author_rank: Super Contributor
timestamp: October 12, 2017, 01:55:44 am
content: A lot of the reputation "live-chassis" sets have comes from the bad old days of vacuum tube rectifiers and unpolarized flex. TVs from that era did not have video in jacks because they would be unsafe, since the mains might be conducted onto the shield of the video cable!Even if a computer monitor is not fully isolated, it can't literally be live on the chassis without conducting the mains into the computer equipment. While it may be good practice to use isolation transformers, it is not the same level of risk as the former designs.

author: BubbaMc
author_rank: Contributor
timestamp: October 12, 2017, 04:21:36 am
content: Good to know, thanks.

author: djos
author_rank: Unknown
timestamp: October 13, 2017, 10:01:14 am
content: So I'm finally recovered from a nasty dose of Gastro and made it back out to the workshop to finish off my 1084s repair:Old switch gone:new switch in:Picture quality tweaked to perfection using my little a600 (finally found a use for it! Workshop Amiga!):yeah baby:Soooo, i was very happy .... until the new switch failed after half a dozen uses!Wagner Online are going to be getting a very sternly worded email from me shortly!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 18, 2017, 10:53:34 pm
content: I had no idea there was a 1084 with a bezel looking like the 1950. Thanks for sharing!

author: djos
author_rank: Unknown
timestamp: October 18, 2017, 11:13:18 pm
content: Quote from: Alex Eisenhut on October 18, 2017, 10:53:34 pmNo worries.There are a whole bunch of Philips and Daewoo based Commodore monitors that look like this including the 1083, 1084 & 1085. Here's a great resource that even has pics:http://gona.mactar.hu/Commodore/monitor/Commodore_monitors_by_model_number.htmlPS, the 1950 does look a bit different tho:

author: djos
author_rank: Unknown
timestamp: October 18, 2017, 11:20:11 pm
content: Btw, Wagner Online have sent me a new Power switch so hopefully it'll arrive shortly.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 18, 2017, 11:22:40 pm
content: I'm just baffled by the sheer amount of monitor models C= pumped out. Why so many?

author: djos
author_rank: Unknown
timestamp: October 18, 2017, 11:26:20 pm
content: Quote from: Alex Eisenhut on October 18, 2017, 11:22:40 pmThey were all made by 3rd parties so that likely has something to do with it. They did also have to keep adding support for different video standards in use by the Vic20, c64, c128, PC and Amiga models

author: djos
author_rank: Unknown
timestamp: October 18, 2017, 11:30:33 pm
content: And lets not forget the various world voltage standards 110v & 220v plus the different power/video frequencies 50hz and 60hz.

author: djos
author_rank: Unknown
timestamp: October 21, 2017, 08:05:42 am
content: So my replacement switch arrived yesterday and has now been installed. The monitor works great with Analogue RGB (picture is perfect) but I'm seeing some weirdness with TTL-RGB (aka CGA), picture is soft and colours are weird (white text is pinkish and soft) so it looks like I might need to check a few more things on it.

author: 108CAM
author_rank: Contributor
timestamp: October 20, 2023, 03:52:30 am
content: Bringing this thread back because I have a Commodore 1084S monitor that I took out of our attic because my interest in computers has resparked and I'd like to see if it still works.I know some stuff about CRT displays and the hazards associated with them in regards to high voltage that can still be present long after the monitor has been switched off and unplugged. Well in my case, the monitor has been sitting without power for over 20 years so I doubt that there's still any voltage left inside. My main concern is that the electronics have sat unpowered for so long that they may no longer work.Here's a photo of the monitor.Yes it's tied up with Telstra Rope. I did this so I could lower it from the attic in a (mostly) safe and controlled manner without shattering the picture tube or falling off the ladder and having a computer monitor hit me a few seconds later.Back to the monitor now.I know how violent a CRT implosion can be. I've seen videos on YouTube that showcase how violent a CRT can be if it implodes. I also know that the flyback transformer and it's circuitry are where the high voltage that everyone warns everyone about is located and that discharging the capacitors and removing the suction cup from the tube is the first thing you should do after unscrewing the casing.Lastly, whenever I'm working on something and feel that what I'm trying to do is outside my confidence level, I won't do it until I feel confident enough to do so or I have someone else who can do the work for me.Hopefully I can get it working. My ultimate goal is to acquire a C128 system to use with the monitor as it was a very common combination for it's time.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 20, 2023, 06:29:04 am
content: Quote from: 108CAM on October 20, 2023, 03:52:30 amMany of the warnings about implosion of picture tubes are a relic of the very early days of large (for then) CRT tubes, mainly WW2 military PPI RADAR displays, where the glass thickness was very much less than later tubes, partly for Wartime austerity reasons, but also because it was difficult enough to obtain sufficient brightness, even without the optical losses of heavy glass construction or heavy safety faceplates.With the rapid development of domestic TV receivers, real world practicality demanded much more rugged tube construction, whilst, fortunately, coinciding with much more sensitive phosphors & more convenient methods of producing EHT.For a number of years, these were combined with separate glass faceplates, then, coincident with the replacement of 17" & 21" tubes with 19" & 23" types, bonded faces were fitted.The latter development was in the very early 1960s.Later, "prestressed" designs were used, which concentrated any implosive forces away from the screen, into the very much smaller neck area, where the amount of glass available to possibly cause damage is much less.After a general, but not close, association with CRTs for years, I changed jobs & became, as one of my duties, in charge of "Monitor Maintenance" at a TV Studio.During my 10 years there, I worked inside many monitors & changed a large number of picture tubes.The dead CRTs were taken out the back of the building & chucked (from a safe distance) into a large metal dumpster.Mostly, the necks were broken on impact, with a gentle sigh, & that was that.Some survived such treatment, so for those, we had a long length of metal "star picket" which we used to crack the necks, with the same gentle sigh resulting.As the Commodore Monitor was a mid-late 1980s product, its CRT would have had all of the later developments included, as well as being a quite small tube to begin with.As to EHT, if it is working, you have little reason to mess with it.The manufacturers provide quite good insulation, so inadvertently touching it is most unlikely.What you might encounter is the several hundred volts of horizontal or vertical signals on the deflection yoke, which can give youa nasty surprise but are not a serious danger.What really are the BIG "bities" are those places which are fed from the Mains, like the power transformer primary, if one is used, or more probably the SMPS (note; these also have nice big electrolytic caps charged to rectified Mains), & lastly, the thermistor in line with the degaussing coil.

author: 108CAM
author_rank: Contributor
timestamp: October 20, 2023, 10:33:09 am
content: Got some good news!I cleaned off the dust, checked over the electronics and gave it the All Clear for testing.The first test was inconclusive because the power button popped out. (This is a very common issue with Commodore 1084 series monitors)Second test and first "real" test (I say real because it had power this time) and it fired up like it was fresh out of the box!This photo paints a thousand words when it comes to "They don't make things the way they used to"Screen is grey because there was no video input. I did connect a VCR to do a more accurate test and it looked and sounded great.Very happy to have it working while learning a bit about CRT tubes along the way!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 20, 2023, 02:03:32 pm
content: I had a 1084 for my Amiga and it didn't look like that, one of the things about Commodore that still amazes me is the sheer amount of monitor models they put out.I have a 1080 now.

author: 108CAM
author_rank: Contributor
timestamp: October 21, 2023, 12:04:43 am
content: Quote from: Alex Eisenhut on October 20, 2023, 02:03:32 pmI'm also amazed at how many monitor models Commodore had, especially with the 1084 series on its own.Here's some history about the 1084 for anyone who is curious.The 1084 was made in quite a few variations. Older 1084s have the power button on the front and the input plugs on the back were updated multiple times during the time the 1084 was in production. The 1084 was originally equipped with round DIN style connectors and the 4 RCA jacks. The DIN ports were later replaced with an RGB port that looks similar to a VGA connection but only has 9 pin holes.Many older 1084s have a knockout plate for a SCART connector however the connector was rarely used. I have yet to see a picture of a 1084 with a factory installed SCART connecter.Another thing that was changed is the design of the stand. It was originally located under where the screen is but was later redesigned and moved in closer to the middle, perhaps for better weight distribution since the front of the CRT (including the glass safety panel that is stuck to the front of the tube) is the heaviest part and the original stands were pretty much holding most of this weight.The design of the stand may have also been a result of when Commodore changed OEMs for the 1084. The original 1084s were manufactured by Philips and were basically rebranded CM8833 monitors in white cases. The newer 1084s were manufactured by Daewoo in Korea and the design saw some alterations. The supplier of picture tubes also changed at least twice during the Daewoo era. I've seen 1084s with tubes made by Samsung and Orion. (Ironically, my 1084 is a Daewoo unit and it's main board has a Philips chip on it!)Other minor changes included the design of the Commodore badge, bezel design, vent/speaker holes, case shape and circuit boards.Any 1084 with an S in it's model number is a stereo unit, regardless of if the OEM was Philips or Daewoo.As for my 1084, It's a 1084S-D2 manufactured in October of 1992 and apart from the power button not staying pressed in (Common 1084 issue), everything else is in working order. The front flap which is almost always broken on 1084s is intact and the press to open mechanism still works perfectly. The only other thing that may need adjustment is the control knobs for the picture and brightness. I also need to find a video source that I can use to check if the vertical and horizontal holds need adjustment.

author: helius
author_rank: Super Contributor
timestamp: October 21, 2023, 03:18:37 am
content: Quote from: 108CAM on October 20, 2023, 03:52:30 amThere's a saying that a little knowledge is a dangerous thing.Much of the above is hearsay, outdated information, or inaccurate. Post-1960s CRTs with metal bands generally do not implode at all. If the vacuum is broken they make a farting sound and that's about it.The truly lethal section of a monitor is the power supply circuitry which often has no separate shielding; not the flyback or anode.Removing the anode cable is not "the first thing" you should do! In fact it is almost never necessary to do it at all, unless access to other parts (most often the cause of failures, for example the horizontal output transistor or the sync circuits) requires it.

author: DTJ
author_rank: Super Contributor
timestamp: October 23, 2023, 01:52:40 pm
content: Quote from: vk6zgo on October 20, 2023, 06:29:04 amThey were very tough tubes.As a child of the 70s I spend many an hour at the local dump or in the bush tossing bricks at dumped TVs.It often took many tries aiming at the front of the screen. When they went, they went very well!Bricking the rear of the tube was a lot less exciting.Good to see you still about vk6zgo, we spent a year or so working together around 2002.

author: petervg
author_rank: Newbie
timestamp: January 11, 2025, 09:18:57 pm
content: About the switch: I also have a 1084S-P1 with a broken flyback and a non functional powerswitch. I took the switch apart to see if it could be repaired or at least to see why it failed. Honestly I don't think it's worth replacing the switch with the same one as they don't seem to be designed to last very long.The switch uses the same technique as the IBM model M keyboard to move the contacts from the closed position to the open position. The mechanism that makes the button hold is indicated in the pictures attached.Problem: the stud that rides in the tracks to hold the button is very very very fragile. The tip that rides in the tracks is a small 0.5mm protrusion that simply wears off very quickly. You could try and 3D print this part, but the design is just not made to last.Not sure if anyone cares, but just my 2 cents