sony msx HB-75P picture problems

Supporter (6)

03-10-2022, 16:08

hello friends i get only vertical lines on from my msx HB-75P i use scart and RF cables and flat and CRT monitor its all the same lines that change to color when i press Return... anyone know what is this about... thanks in advance.
pictures bellow.
https://postimg.cc/hf04KtrC
https://postimg.cc/dkKtqkzx

By AndreV

Master (232)

04-10-2022, 11:57

Maybe this post helpt,

https://msx.org/forum/msx-talk/hardware/sony-hb-75p-freezes?...

By AndreV

Master (232)

04-10-2022, 11:59

First try to remove the big chip under the smal pcb, and inserts again, see what happens can be the contacts of the chip leg, easyto try.

By frogyfogy

Supporter (6)

04-10-2022, 21:31

well it would be nice if it would be so ease.. i remove the big Sharp chip and the other two removable chips as well one by one to see if its some of them with bad contact but no the problem was not solved. still same picture with lines and the thing is that the computer is in a really nice condition no dust rust or any leaching capacitor it looks like new inside and out came with original box with all the manuals and a data cartridge. looks like it was really not used a lot or even at all... and when i open its showing this lines picture in color and then after 2 seconds turning it to black and white after that if i press Return on the keyboard its turning it to colorful again and if i press something on the keyboard its even sound click like its tipping especially if i hold a button and working just i don't see anything only the lines on monitor.
https://postimg.cc/B8cxsm6X
https://postimg.cc/GT0Km4Rp

By AndreV

Master (232)

05-10-2022, 09:51

https://www.msx.org/forum/msx-talk/hardware/sony-problem-hb-...

Have try to get to basic,? Skip the internal rom I've you have a game cartridge?
I think its the vram, i had changed in my msx all 8 vram chips, bud my case was the video chip bad contact, vram to change you have to solderen them out, took some time, those rams can get faulty with age. Swap the 4116 VRAM with 4164 VRAM,

By frogyfogy

Supporter (6)

06-10-2022, 21:12

unfortunately i don't have a game cartridge.. i try ti make it BEEP but it didn't sound a thing. i know that the ram may be faulty but maybe its not the ram maybe its some other chip so before i start to change staff on the motherboard i would like to know if anyone had ever see something similar and may point me to the right direction because with this things it can be many that can be faulty and you may only find out when you change half motherboard of chips... anyway any help is welcome i would like to try the easy stuff before i go to desolder-solder-check solution

By AndreV

Master (232)

07-10-2022, 10:48

Maybe you can piggy bag the vram i've you have a good 4116 vram like in this video, whitout soldering i bought 8 vrams 4116 for 10-15 euro's there salvage from othter computers, otherwise i ran out of ideas.
Its a trail and error, and a bit of luck.
feel with ram runs hot 4116 run hot bud can't take more the 70C , i've its a smal resitor or a broken solder that's verry hard to detect or recognice.

https://www.youtube.com/watch?v=e8psx5EXlB4

By frogyfogy

Supporter (6)

07-10-2022, 14:28

ok thanks for the help AndreV i will try this steps but its hard to me to find ram chips on ebay.. where you find yours? mast search on some other site..

By AndreV

Master (232)

07-10-2022, 17:20

https://www.bytedelight.com/?product_cat=ramchips (bought mine here, it was 1 halfs years a go)

https://www.retroleum.co.uk/zx-spectrum-chips

By frogyfogy

Supporter (6)

08-10-2022, 11:07

so i can swap the 8x4116 ram chips with the 4164 Spectrum "Upper RAM" Chip it will be compatible without modifying anything else just desolder and solder new ram?

By AndreV

Master (232)

08-10-2022, 14:39

https://youtu.be/OJHPgS2Eg00

10 minuters in to the clip you can see how to modify the 4164 verry easy