Audio , no video

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By somacast

Resident (34)

somacast's picture

15-05-2021, 00:43

hi ,

aside from my previous unanswered topic , i tried to grap a used motherboard for my problematic A370 (MSX2) Arabic version.

the new board has no video out , only audio , any clues please?

also wanted to ask about some keyboard buttons not working ( 2 , esc , e , u ) , doesn't seem like contacts of keyboard issue, what could be in motherboard?

thnx

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By Grauw

Ascended (9906)

Grauw's picture

15-05-2021, 03:26

somacast wrote:

the new board has no video out , only audio , any clues please?

Is it the case for both the composite video and RGB outputs?

somacast wrote:

also wanted to ask about some keyboard buttons not working ( 2 , esc , e , u ) , doesn't seem like contacts of keyboard issue, what could be in motherboard?

Bit 2 of the key matrix is out of order. Check if the keyboard connection ribbon cable is plugged in properly and does not have any breaks in it or bad contacts. Try cleaning the ribbon contacts carefully with an eraser and then isopropanol alcohol.

The Sanyo WAVY PHC-70FD that I used to have (on which the Sakhr AX-370 is based) had a bad keyboard connection as well, it seems this is a fragile part of this machine.

By somacast

Resident (34)

somacast's picture

15-05-2021, 03:44

Quote:

Is it the case for both the composite video and RGB outputs?

thnx for replying , currently only composite, i will make an RGB cable today and see

Quote:

Bit 2 of the key matrix is out of order. Check if the keyboard connection ribbon cable is plugged in properly and does not have any breaks in it or bad contacts. Try cleaning the ribbon contacts carefully with an eraser and then isopropanol alcohol.

The Sanyo WAVY PHC-70FD that I used to have (on which the Sakhr AX-370 is based) had a bad keyboard connection as well, it seems this is a fragile part of this machine.

the connector is good, ribbon is well clean, i even gave connector socket a fresh solder, i tried by a multimeter checking if pressing these buttons does give a reading from both ribbon cables, and it seems it does , not sure whats wrong..

By somacast

Resident (34)

somacast's picture

16-05-2021, 18:15

update:
i can confirm its working perfectly by RGB output

now what causes the AV to output only audio ? any hints?

thnx

By somacast

Resident (34)

somacast's picture

18-05-2021, 00:53

Grauw wrote:
somacast wrote:

the new board has no video out , only audio , any clues please?

Is it the case for both the composite video and RGB outputs?

somacast wrote:

also wanted to ask about some keyboard buttons not working ( 2 , esc , e , u ) , doesn't seem like contacts of keyboard issue, what could be in motherboard?

Bit 2 of the key matrix is out of order. Check if the keyboard connection ribbon cable is plugged in properly and does not have any breaks in it or bad contacts. Try cleaning the ribbon contacts carefully with an eraser and then isopropanol alcohol.

The Sanyo WAVY PHC-70FD that I used to have (on which the Sakhr AX-370 is based) had a bad keyboard connection as well, it seems this is a fragile part of this machine.

so any further help please? I tried cleaning the video port but no use, I know it works fine with RGB however I just want the AV out to work as well, thanks

By sdsnatcher73

Paragon (1981)

sdsnatcher73's picture

18-05-2021, 05:01

I am not a hardware guy myself but I have had many MSX’s fixed by other people. I am also not familiar with the AX-370 or the Arabic MSX’s in general (I have mostly seen European and Japanese MSX’s). However I suspect that the AX-370 is a PAL machine, is that correct? If it is there is probably an LVA510 chip somewhere (possibly on a daughter board). This chip is the PAL encoder chip and is a known culprit of no video signal. Check the capacitors around the chip and if they are good it’s probably the chip itself that has died.

By somacast

Resident (34)

somacast's picture

18-05-2021, 11:51

sdsnatcher73 wrote:

I am not a hardware guy myself but I have had many MSX’s fixed by other people. I am also not familiar with the AX-370 or the Arabic MSX’s in general (I have mostly seen European and Japanese MSX’s). However I suspect that the AX-370 is a PAL machine, is that correct? If it is there is probably an LVA510 chip somewhere (possibly on a daughter board). This chip is the PAL encoder chip and is a known culprit of no video signal. Check the capacitors around the chip and if they are good it’s probably the chip itself that has died.

thanks alot i will check that

By sdsnatcher73

Paragon (1981)

sdsnatcher73's picture

18-05-2021, 12:55

You can make some pictures of the mainboard as well, that will definitely help more knowledgeable people to identify possible things that could go wrong and direct you in your efforts. No pictures of the mainboard exist in the Wiki as for now.

By somacast

Resident (34)

somacast's picture

18-05-2021, 15:16

sdsnatcher73 wrote:

You can make some pictures of the mainboard as well, that will definitely help more knowledgeable people to identify possible things that could go wrong and direct you in your efforts. No pictures of the mainboard exist in the Wiki as for now.

just uploaded photos

https://ibb.co/tYN8nTB
https://ibb.co/ryVJfFN

my board doesnt have that chip

By Pencioner

Scribe (1423)

Pencioner's picture

18-05-2021, 15:27

looks identical to Sanyo Wavy PHC-70FD - which is not a surprise anyway

By Alexey

Guardian (3120)

Alexey's picture

18-05-2021, 15:47

The problem is most likely in MC1377P encoder or its surrounding elements. The board is so dirty and rusty that I really wonder how it still works. According to my previous experience with Yamaha video boards in similar condition, any through-hole element could rust out and loose connection to the board, for example a transistor's pin could look intact, but when you slightly bend it, it snaps off because it rusted out.

If you plan to sell the broken motherboard, I would be willing to buy it from you.

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