NMS 8280 RGB output vertical lines/quality

Champion (392)

28-04-2020, 20:43

Need some help/advise for the vertical stripes (wobly) / output quality.
On my Anacona monitor the output quality was very good, noticed no issues. (Monitor stops after a few minutes so and needs to cool down to work for a few minutes again ).
Tested on a Samsung 32B650 connected on the scart it looks like this (bit of distortion not visible)
Tested on a Sony 42W706b it looks like this
Tested on my KME LPT scaler it looks like this
Tested on my DVD Iscan HD scaler it looks like this and this (check the letters)

Hoping for some tips or experience.
Is this the psu diode problem?
Can a Sync Strike fix some of the problems?
The DVDO seems to show the best results but looking better it does strange things with the output.
Already many thanks in advance.

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By Grauw

Ascended (10821)

28-04-2020, 20:58

For the jailbars (vertical stripes), it sounds like a problem with aged electrolytic capacitors which need to be replaced. It seems those in the power supply go bad, check "Jail bars" in RGB output of Philips NMS 8250 for further discussion on a similar machine. Particularly the posts by RetroTechie and Philip, where Philip said that recapping the power supply and replacing two diodes fixed it for him.

A wobble in the vertical direction as seen on your DVDO iScan HD scaler indicates a CRT monitor photon beam stability problem, not a signal problem. Or in this case, if the output is digital, a problem in the scaler. So a sync strike won’t do you any good probably. The signal sent scans lines from left to right, the monitor is responsible for making sure the lines are straight and in this case it seems it isn’t.

By shaiwa

Champion (392)

28-04-2020, 21:43

Thnx Grauw for the fast reaction and clearing up doubts needing a Sync Strike.
Also about the "Jail Bar"topic, was not sure it was the same problem because on an old RGB monitor it looks fine.
DVDO Scan HD has a known 240p bug but didn't realize it was this bad, bumber the rest looks so good
Have to do some shopping then to get the replacement components, it has been years i did some soldering.

By Daemos

Prophet (2170)

28-04-2020, 21:48

If you have the tools. Before you start soldering. Check the power supply with a scope. Replacing many capacitors to then find out you did it for nothing can be annoying. Off course only if you have a scope

By shaiwa

Champion (392)

28-04-2020, 23:41

Got no scope unfortunately, little repair experience also but have done some soldering in the past and have basic ESD protection equipment.
Think starting first with visual inspection of the caps and then start with the PSU fixes asap.
Have to order the componets so may take some time to get started.

By shaiwa

Champion (392)

29-04-2020, 16:34

Did a visual inspection but caps looked fine to me.
Measured the psu pins:
Pin 1, service manual = +12V, measures +12,01V between pin 1 & 3
Pin 2, service manual = +5V, measures +5,18V between pin 2 & 3
pin 4, service manual = -12V, measures -18,86V between pin 4 & 3
Guess -12V is not ok or did i measure wrong?

By meits

Scribe (6577)

29-04-2020, 16:52

Caps are broken if they look broken. They're not automatically good if they look good. Even measuring them can be a pain. Replacing them is cheaper than getting the required tools.
-12V looks off... Voltages are allowed to deviate 10%.

By shaiwa

Champion (392)

29-04-2020, 17:46

Thanks Meits, so going to replace the PSU caps and diodes mentioned earlier and i think reading this replace IC1052 should fix the -12V.

By donluca

Expert (75)

01-05-2020, 23:43

Damn, I just looked at my NMS-8280 and realized I have the damn jailbars! I didn't notice them at the beginning and now I can't unsee them.

Oh well...

By shaiwa

Champion (392)

04-05-2020, 15:49

Lol, guess it happend to me too dunluca
Had contact with repairbas, because i could not find the correct diodes.
Luckily he had the correct ones at stock, also bought the -12V voltage regulator from him.
Replaced IC1052 and diodes D1050 - D1053, didn't resolve the vertical stripes but the image seems a little less noisy and more stable.
Think I'll replace the PSU caps, just to know if it does fix the jail bars or not.

Got this weekend myself a SLG in a Box, know the scaler isn't great but it has a buildin sync strike and image is nice but not very sharp.
So now more systems to test with , seems the diy cable i made for the KME LPT scaler seems to be the cause of the very noisy image so i'll build another one asap.

By donluca

Expert (75)

04-05-2020, 15:55

Keep us updated!

I'm using with a Sony BVM Pro monitor, it has the jailbars and little horizontal shake, but only when set at 60hz.

Need to check what components I have available.