Phillips CM8833 II monitor still faulty after fitting new flyback transformer

[Stardust]

I have a Phillips CM8833 II monitor that failed last year. When it failed there was a single very bright white horizontal line. And a minute later nothing.

Today I removed the original HR 7555 flyback transformer and fitted a new one. Unfortunately the monitor is not fixed. Powered on it goes from a blank screen after a few seconds to a dim light gray screen with horizontal lines. Over a total of ten seconds the screens gets much brighter to a bright white with horizontal lines. I took a digital photo but the image is totally washed out with the white from the CRT. I put the two dials on the flyback transformer to a middle position.

I followed the Retro Man Cave youtube video on how to do a flyback transformer replacement for this monitor. I took my time but I did one thing differently. I spliced the black wire that goes from the white multi pin socket that connects to the back of the CRT. I soldered that to the new black wire on the flyback transformer. I used 4 layers of heat shrink because the wire handles around 25,000 volts. If RMC had difficulty taking apart the white CRT connector to remove the original black wire then that probably would be beyond my novice electronics skills.

Is there something I can do to fix it? If not I will sell it as faulty on ebay.

[dlfrsilver]

What model of flyback did you used to replace the HR 7555 ?

For this model, the replacement flyback is the HR 7533.

[Stardust]

I need to backtrack. It seems I have confused myself.

The original flyback transformer has a label with "AT2079 37591". It was not a HR 7555. I ordered a replacement HR 7533 flyback transformer which I have fitted. Retro Man Cave youtube channel used a HR 7533 as a replacement for his Phillips CM 8833 II monitor.

[Stardust]

On my invoice from Donberg Electronics and the product webpage it implies that the HR 7533 and AT2079 37591 are the same https://www.donberg.ie/descript/h/hr_7533.htm

[dlfrsilver]

Ok that's good. you have something else wrong that need a replacement.

And the final setting once everything is in place.

[mech]

I am not A monitor expert but sounds like vertical deflections is gone if you have a horizontal line. either a vertical IC,parts in the path or a power supply issue?

[Stardust]

There are many horizontal lines on a very bright light gray screen.

[Snoopy1234]

Most Crt flyback blogs I've seen mention the "HOT" as needing replacing in conjunction with the flyback. It's a transistor in the immediate circuit that gets overloaded and fried when the flyback goes.

[giantclam]

Originally Posted by Snoopy1234

Most Crt flyback blogs I've seen mention the "HOT" as needing replacing in conjunction with the flyback. It's a transistor in the immediate circuit that gets overloaded and fried when the flyback goes.

Horizontal Output Transistor ...it drives the EHT (flyback) transformer .... TS467 (BU508A) ...D465/467/468 should also be checked

[Stardust]

Looking at schematics for the Phillips CM8833 II monitor from this pdf download https://elektrotanya.com/philips_cm1.../download.html I can see that there is only one BU508A type transistor: Page 28 text "7512 4822 130 61265 BU508AF". This has a connection to the flyback transformer. Should I get a BU508A or BU508AF transistor variant?

But I can't find any components that relate to "D465/467/468".

[giantclam]

https://ia800703.us.archive.org/19/i...pscm8833sm.pdf

Get BU508A (it dissipates 125watts, the BU508AF can only handle 50watts)

You'll see the diode in above pdf

[Stardust]

Ordered BU508A transistor. Also RGP10D diode for "D465", BY458 diode for "D467", BYV95C diode for "D468".

Thank you for the help.

[pandy71]

Horizontal line present on screen may imply that flyback is OK same as H line part - issue can be in vertical deflection.

Instead blindly replacing components (expensive ones) i would rather suggest to verify with oscilloscope most important points - to not destroy oscilloscope (end prevent electrocution) it is recommended to power monitor and oscilloscope probably it is best to use galvanic separation (such as separation transformer) and some current limiter (even high power incandescent bulb with 150..250W can be fine).

Sorry mech, just read your comment after mine - obviously you pointed that it may be issue with vertical deflection

[Stardust]

I took a photo of the monitor in its current state that is not washed out. Only a little blurry.

[pandy71]

It will be interesting to see how it looks before flyback replacement - you have obviously HV and some horizontal deflection but it looks like voltage on CRT tube is not OK (to high ? on tube grids?) - from my perspective this is black screen with visible horizontal return lines - normally they shall be not visible.
Buy oscilloscope, take https://www.nightfallcrew.com/wp-con...ice_Manual.pdf or https://www.arcade-museum.com/manual...s%20CM8833.pdf, use some video source (DVD, media player) with useful patterns (like grid) so you be sure that there is proper video and sync at the monitor input.

[Stardust]

In the first post I said I have already replaced the flyback transformer

[pandy71]

Fine (issue is that flyback in first place can be OK if something else failed) - https://www.ti.com/lit/an/snla017/snla017.pdf this can be interesting lecture - you need to verify if power part is properly driven - if issue is somewhere else then replacing flyback and power transistor may be very short term solution...

[UberFreak]

Originally Posted by Xav

I put the two dials on the flyback transformer to a middle position.

Is this really how you adjusted Focus and G2 voltage?


Too high G2 = grey screen with retrace lines.
Check the service manual for the correct G2 voltage and adjust using a multimeter.

[Photon]

Had two of these, gave up cos no component source. In 2009, so not bad quality maybe but MKI still going. And generally CRTs last forever.

My only advice is unless the obvious like burn marks on boards, blown fuse, wrong voltages by multimeter - keep hands OFF unless you've repaired a CRT monitor before, it can kill you(!)

You can buy an oscilloscope and check the other obvious, frequencies from H/V circuit, but you can also die from poking your hand in there live again and slipping...(!)

Unlike most all other computer electronics I say send to local TV repair guy if you are unsure. Even with flatscreen TVs now, some know how to do this blindfolded.

[Stardust]

The three diodes and one transistor will be replaced. If that does not work I will not venture further in trying to fix the monitor. I know how to discharge the CRT but I am not going to start doing stuff with an isolation transformer, oscilloscope and turned on monitor. I could take the monitor to a local electronics repair shop.

I have two Phillips CM8833 II monitors. Today I used the working one and loved the picture quality with retro computer game graphics.