Sony hit bit HB-75P won't start

Page 4/4
1 | 2 | 3 |

By sdsnatcher73

Paragon (1646)

sdsnatcher73's picture

22-02-2021, 04:21

It‘s conceivable that the 4116 chips were causing the interference on the power signal, anyway good job and thanks for sharing the outcome.

By popolon_

Master (151)

popolon_'s picture

26-02-2021, 19:01

I put original composite sync signal back to scart, and the picture has no problems in RGB mode, so the sync separator LM1881 is not necessary, at least not in my LG LCD TV case. But that blanking signal scart pin 16 connection via 150ohm resistor to +5v was necessary to get RGB mode from TV. I tried also the composite video signal in LG TV, but then there was noticable ghosting or something. So either LG TV is bad at handling hitbit type input, or hitbit is outputing quite bad composite video. I did not notice this bad picture from toshiba hx34 composite output to this same LG TV.

By sdsnatcher73

Paragon (1646)

sdsnatcher73's picture

26-02-2021, 19:28

But did you get rid of the jailbars? On my LCD TV I use for testing I have not seen them and sync was always good (I’ve encountered 9 HB-75P and variants so far). Only thing that has always struck me as odd was the very blue tint (almost like a haze) of the RGB output. Although 1 of those 9 did not have that.

By popolon_

Master (151)

popolon_'s picture

26-02-2021, 19:55

yes, no jailbars (RGB or composite video). So VRAM chips with single voltage chips was enough to get rid of jailbars. LM1881 did not have effect on those.
However it seems the voltage reference levels are not same for all colors, but the Vpeak to peak is same for all colors (I tried to adjust these to have same peak-to-peak). R=1-1,9v (Vp-p = 0,9v), G=1,2-2,1v (Vp-p=0,9v), B=1,0-1,9v (Vp-p = 0,9v) when connected to TV.
I also notices some resistors are different in pcb than in the service manual pictures. for example R56/R73 (blanking signal output).

Page 4/4
1 | 2 | 3 |