Sony hit bit HB-75P won't start

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By Lars Bolstad

Supporter (4)

Lars Bolstad's picture

02-02-2015, 20:11

Hello, this is my first post here. I have tried searching the forum but didn't find any answer.
My Sony Hit Bit 75P, when i turn it on, only displays a blue screen.
No text or sound, only a blue screen.
I have measured the 5, 12 and 17 volt, and it seems fine.
Do someone have any idea what could be wrong?

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By Grauw

Ascended (9578)

Grauw's picture

02-02-2015, 22:03

If you type, do you hear the key clicks coming from the speaker? If so, what happens when you type (blind) COLOR 15,4,4 or COLOR 15,0,0?

By Manuel

Ascended (17484)

Manuel's picture

02-02-2015, 23:10

Perhaps the built in ROM is somehow broken or not completely in anymore. Try to push the EPROMs on the motherboard to make sure they're still connected properly.

By Lars Bolstad

Supporter (4)

Lars Bolstad's picture

03-02-2015, 12:21

I have tried pushing on the eproms, and taking them out and mounting them in again with no luck.
I've read that the roms can get bad over the years and can get leaky, is there any way of checking if they are still intact?
Bying a eprom reader from ebay and see if they still holds the rom maby?
I will try the blind writing method when i get home from work today, and see if that works, and if i hear any sounds.

Thanks for the tips so far :-)

By Lars Bolstad

Supporter (4)

Lars Bolstad's picture

03-02-2015, 18:42

I hear no key clicks, only a buzzing noise. Also, the cap light is on all the time.
Nothing happens when i type the color commands. Crying

By Manuel

Ascended (17484)

Manuel's picture

03-02-2015, 20:44

I'm not an expert at all, but my guess would indeed be that a ROM is broken...

By Grauw

Ascended (9578)

Grauw's picture

03-02-2015, 20:47

Hmm yes, sounds likely to me too.

By msxholder

Champion (369)

msxholder's picture

03-02-2015, 22:23

Athe start of this question
Out of the 4e line there should not be an 17 volt
If it is true than there must be blown up Parts
An msx has minus 12 volt ,plus 5 volt and plus 12 volt

By Lars Bolstad

Supporter (4)

Lars Bolstad's picture

03-02-2015, 23:21

Ok, my bad. When measuring out of the power/video board, there is +5, +12 and -12.
The 17 volt is when i measure between the +5 and -12. Sorry for the confusion.

By popolon_

Expert (127)

popolon_'s picture

22-01-2021, 16:56

This is old thread, but did the problem got solved?
As I have same situation now also (HB-75P).
I have measured voltages and all are fine. However +5v line is 4.86v in memory pins and ROM socket pins (in power circuit output it is 4.96v).
I have dumped all three roms, and those are identical to the roms found from this zip http://www.msxarchive.nl/pub/msx/emulator/openMSX/systemroms... .
I tried even booting without these rom chips, and same symptoms was shown (blue screen).
I did not see any obvious black traces in mainboard as was the case in some of hitbit startup problems in here.
With oscilloscope I measured clock signal in Z80 clock input. Maybe I have to next check that every address line and data line goes from rom chips to Z80.

By popolon_

Expert (127)

popolon_'s picture

09-02-2021, 18:13

There was broken signal from IC38 PIN 2, towards BASIC ROM PIN 20 (rom II ). It was not so easy to spot. I also changed IC17+IC23 near PPI chip as there was at least some heat marks there. Also PPI pins had some heat marks, but i did not change that yet. Anyway the hitbit now boots up, the screen however now jumps up and down for few pixels, and also jumps left and right sometimes. This is with picopsu, so there is problem with capacitors in video side.

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