Question on re-assembling Sony HB-F700

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By Alexey

Paragon (1163)

Alexey's picture

10-07-2017, 23:58

Hmm, seems that the GB50H is originally 3.6v. So I guess I'll install it, but with the possibility to remove it in case I need to clear the settings.

By Alexey

Paragon (1163)

Alexey's picture

20-09-2017, 02:38

Louthrax wrote:
Alexey wrote:

Another MSX brought back to life from the dead! Mes félicitations!

Merci Smile That was not too hard with a new board, you'll have a greater challenge trying to resurrect my dead board Smile

Mission accomplished, well, almost. I had to change 2 chips on the main board and also the VDP: now the machine at least boots to Basic. However there's still one problem - it does not boot from a floppy drive. Will try to find the reason.

Btw, for the repairs I had to use the VDP that was cut by someone from a different board. The cut pins were short and twisted, so it took a while to fix the mess. Here's how it looks now:

By Meits

Scribe (4466)

Meits's picture

20-09-2017, 03:29

That's an impressive job you did there.

By Alexey

Paragon (1163)

Alexey's picture

20-09-2017, 08:45

Thanks. Smile Any idea how to diagnose the floppy controller's faults? It tries to boot, but doesn't read the data. The drive spins for a few seconds. I set the read pulse and vco according to the service manual, but seems that vco is sometimes disappearing...

By Meits

Scribe (4466)

Meits's picture

20-09-2017, 11:56

I'm not a techie, but I do have a sony 700 here which refuses to use the FDD as well. My temporary solution was to hook up a drive to the backside of the machine configured as drive A: That did work.
As the internal cable does not show a break after measuring, I guess there something wrong elsewhere. If you have a similar situation, I'd love to read details if you fix it. I am able to change components, that's where my skills end Wink

By Louthrax

Paragon (1639)

Louthrax's picture

21-09-2017, 13:19

Alexey wrote:

Thanks. Smile Any idea how to diagnose the floppy controller's faults? It tries to boot, but doesn't read the data. The drive spins for a few seconds. I set the read pulse and vco according to the service manual, but seems that vco is sometimes disappearing...

Great job Smile, glad to see that machine alive again Smile A friend gave me this machine in the 1990's because its floppy drive was definitvely not working anymore. I was suspecting the drive, and tried to mount another one instead with no success (later I just used a MegaFlashROM on it). So that seems to confirm the problem is on the board.

Seeing a broken VDP is not that common when repairing machines. Maybe a consequence of the other issues?

By Alexey

Paragon (1163)

Alexey's picture

21-09-2017, 16:50

Louthrax wrote:

Great job Smile, glad to see that machine alive again Smile A friend gave me this machine in the 1990's because its floppy drive was definitvely not working anymore. I was suspecting the drive, and tried to mount another one instead with no success (later I just used a MegaFlashROM on it). So that seems to confirm the problem is on the board.

Possibly the floppy controller chip got busted. I have troubles setting the VCO to 250kHz - it disappears from time to time. The read pulse is always present though. Both logic chips on the controller outputs are ok. So either the controller chip or the VCO components are faulty. This board needs 12v for the VCO regulation and I am not getting a proper reading on the input pin of the regulator...

Louthrax wrote:

Seeing a broken VDP is not that common when repairing machines. Maybe a consequence of the other issues?

Indeed, I haven't seen a broken VDP so far... After exhausting all possibilities on the main board I used the test bios from a Russian developer and it got the registers of the VDP programmed correctly to show the white screen, but displaying a text message failed. The VRAM was swapped and did not affect anything, so the last (and obvious) suspect was the VDP itself. It got somehow partially fried - did not produce the INT signal and was not showing any usable data, only the blue screen on boot.

I was assuming that the VDP board was ok, so I desoldered and checked way more chips on the main board than I should have. Good thing that the board is one-sided and it's easy to remove the chips. Too bad I can't use the keyboard or cartridge slot because I am missing those particular boards. The ripped floppy cable I was able to repair with a prototype board and angled 34 pin connector. And some hot glue... Wink

By Alexey

Paragon (1163)

Alexey's picture

23-09-2017, 22:48

So far with the logical analyzer I have the following when trying to boot from a floppy drive:

Some pictures from the oscilloscope after setting the signals: VCO, READ PULSE and the "saw" on the 26th pin of the floppy controller:

http://podrezov.com/temp/vco.bmp
http://podrezov.com/temp/readpulse.bmp
http://podrezov.com/temp/pin26saw.bmp

Does anyone see any anomaly?

By Alexey

Paragon (1163)

Alexey's picture

08-10-2017, 19:35

Good news - the dead machine is 100% fixed now. The Sony's board needs a working READY signal from the drive. Once I connected the original drive, it worked like a charm. The controller and the rest of the board was not working because of the 2 broken logic chips. The image was not shown because of a partially broken VDP chip.

I got an empty case with a PSU and a floppy drive from Bas and a keyboard (that was assembled from spare parts) from Meits. The keyboard had a broken Enter key, a few broken screw holders and 2 wires were snapped somewhere inside the cable. I had to cut the cable from both ends and then reassemble the 13 pin keyboard plug and solder 14 wires to the keyboard connector on the other end. That took some time and patience. Smile

Thanks to Bas for the good deal on the parts. Thanks to Meits for getting me a fixable keyboard. And of course thanks to Louthrax for donating the boards. We have brought yet another dead machine to life!

Now I need to put in the English BIOS and Subrom into this computer. Can anyone point me to those ROM files? Thanks.

By Grauw

Enlighted (6173)

Grauw's picture

08-10-2017, 20:01

Awesome! Warm fuzzy feeling Big smile.

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