Blurry picture on Philips 8235

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By Alexey

Guardian (2349)

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25-05-2019, 17:01

Check the capacitors in the video out circuit. Also seems that the green signal is completely missing.

By zett

Hero (563)

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25-05-2019, 17:54

yeah. 8235 are great machines and possible to fix.

By ryan.darby.54

Supporter (13)

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27-05-2019, 04:49

I have now obtained a partial refund and I keep the machine. I now need to work out how to fix it. I know nothing. To check capacitors what tool do I use?

By Alexey

Guardian (2349)

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27-05-2019, 08:41

You need an ESR meter and a multimeter at least for the simple diagnostics.

By Mumbly

Resident (49)

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27-05-2019, 23:01

Where are you with your investigations, is it finally the computer that have
Issues ? (Monitor or tv is ok with other device, I presume)
Following the picture the sync h and v are not good, blue seems to be ok but
Green not, since blue and red give purple as you miss green the characters are in purple
Instead of white, isn’t it ?
I will ask to one of my friend what he’s thinking about that, he’s well skilled in the electronic domain
And have already repaired a lot of MSXs.

By ryan.darby.54

Supporter (13)

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28-05-2019, 13:33

I have ordered a multimeter and ECR so will start investigating next week. I still need to try avDIN cable. There are 5, , 6 and 8 pin DIN to RCA cables on eBay, which do I need?

By Alexey

Guardian (2349)

Alexey's picture

28-05-2019, 13:58

The "monitor" output is 8-pin DIN on this computer, but this is not an RGB output that is present on Japanese MSX computers. The board that forms the output contains the LVA510 chip that encodes RGBS signals into a composite video:

The pinout can be found here (look for "Monitor connector Philips"):

https://www.faq.msxnet.org/connector.html

So you basically need the 8-pin DIN to 2x RCA adapter. One RCA is for audio, another - for video. But I would still try to fix the RGB output on SCART because it has native RGB and sync signals.

By Meits

Scribe (5490)

Meits's picture

28-05-2019, 14:58

Multimeters that can measure capacitors normally have a cap that's lower than a lot of the used capacitors. An ESR meter costs quite a few bucks. More than all the capacitors you need. And since you have to desolder at least one pin of a capacitor to measure it, you're already halfway getting it out anyway. I'd freshen up all of them just to rule them out, save money and time measuring.
I've watched loads of capacitor youtube clips and found out that it's not that easy to measure them. A reading with a negative result equals broken, but a reading with a positive result does not per se mean the capacitor is reliable.

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