HIC-1 board redesign and improvement

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By gdx

Enlighted (5014)

gdx's picture

04-11-2021, 01:25

sdsnatcher73 wrote:

The HIC-1 board is used in many different machines, so even if there is no issue in your FS-A1F it may be completely different in e.g. a Sony HB-F1, e.g if tracks are moving in different directions (up-down vs. left-right).

The Sony HB-F1 too does not use the HIC-1 board.

Here are the models that use this board:

Sony:
HB-F1II
HB-F1XD
HB-F1XDmk2
HB-F1XDJ
HB-F1XV

Panasonic:
FS-A1MKII
FS-A1F

Kawai:
KMC-5000 (Panasonic FS-A1F OEM)

Source: http://elec-junker-p2.blog.jp/archives/6089094.html

By sdsnatcher73

Prophet (2529)

sdsnatcher73's picture

04-11-2021, 08:47

Alexey wrote:

One millimeter of air is a good enough insulator. Besides, the replacement board will be 5mm above those tracks because of the socket. The interference may only come from neighboring tracks on the same board. But I hope I routed the board correctly.

I am by no means an expert but my gut says 1mm distance (whatever is in between) is not enough to prevent electro magnetic interference. Do you have a reference for that statement, just trying to understand really by no means trying to say you are wrong Wink

By Alexey

Guardian (3285)

Alexey's picture

04-11-2021, 16:27

I don't have any formulas to calculate EMI's travel at hand, but I am sure there are ones. To cause significant interference a signal going through a wire (track) should be quite powerful. With TTL levels no signal is powerful enough to create EMI that would travel through 1mm of air. Based on my own experience with the early FMPAC designs, I can tell that only if you put your audio signal tracks before the OPAMP very close (less than half a millimeter) away from digital ones, then you might get some interference when the audio signal is amilified. On the first FMPAC board some audio tracks were going under the ROM chip, so the output had a lot of digital noise.

By Alexey

Guardian (3285)

Alexey's picture

21-11-2021, 21:59

Almost assembled, still need the OPAMP and a pair of FMW1...

By sabre470

Resident (36)

sabre470's picture

02-12-2021, 01:37

Wow Alexey, awesome work!!!

Are you going to sell these boards? I have an FSA1 Mk2 in need of a replacement board!

By Alexey

Guardian (3285)

Alexey's picture

02-12-2021, 19:40

No, I am not going to sell the boards, but I will sell a few DIY kits to cover my costs for this project. If someone would want to assemble and sell the boards, we could come to an agreement.

I am in the final stage of debugging the board. I had to do a few patches (see the picture below). The board now works fine - video works perfectly (including S-Video), audio also works well, but there's a slight problem with cassette I/O because the HCT04 chip has different characteristics than the originally used 4069UB and needs a different set of resistors and capacitors. Reading works, but the amplification level is not enough and this sometimes causes Device I/O errors. Even hooking the unused part of LM358 didn't help. So, I am going to try the HC series of the HEX inverter and if that doesn't work either, I will use the original component. It's already on the way to me from China.

By Alexey

Guardian (3285)

Alexey's picture

02-12-2021, 19:51

Just to illustrate the problem - here's the picture. The HCT logic behaves differently than the original 4069 chip, so the signal is not centered at 2.5v, has smaller amplitude and it's also cropped at the bottom. All attempts to fix this by playing around with resistor and capacitor values (as well as by using the OPAMP) failed so far. So, I am going to try the HC series next.

By Alexey

Guardian (3285)

Alexey's picture

14-12-2021, 09:56

I've solved the problem with cassette I/O, one slight problem still remains with the OPAMP. The internal machine's noise is heard in the audio channel while the original board blocks it completely. But the good thing is that now my Panasonic A1F has the official S-Video output on the back. Smile

By S0urceror

Master (195)

S0urceror's picture

14-12-2021, 20:48

Well done. I am sure you can iron out the last little things. The HIC board is unobtanium so a good replacement is great.

By sdsnatcher73

Prophet (2529)

sdsnatcher73's picture

15-12-2021, 06:33

Noise in audio is of course a bit annoying but it’s always relative and there are many MSX models that have noise (well all do but some more than others).

These boards are going to save some MSX’s and that is very important! I like the color of the board as well (it really stands out!).

To improve I think you have to figure out how the noise is introduced in the signal. It may be already present on the inputs of the HIC and the original design had some way of suppressing it (eg a low pass filter). Or it is introduced by electro magnetic interference which could have been handled in the original design by means of that ground plane. But this is tough to figure out I think…

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