M4 and EMI (small) perturbations

[steph072]

Hello,

I experience small EMI perturbation with my new M4 board (little noise in the speaker).
Reboot or strange behaviour of the CPC during massive transfer of data to the board.
My CPC is a 6128, first generation(no shield).

Thank you

[GUNHED]

With the !WIFI,0 command you can switch the Wi-Fi off, then there shall be silence!

Alternative get a German CPC6128, the Wi-Fi based disturbances shall be reduced.

[steph072]

Thanks. Yes, this is what I do. But as it didn't find this subject anywhere, I want to check if it's proper behaviour.

[genesis8]

With the !WIFI,0 command you can switch the Wi-Fi off, then there shall be silence!

Alternative get a German CPC6128, the Wi-Fi based disturbances shall be reduced.

More shielding on a german CPC ?

[poulette73]

Hello,

I have a M4 Board on two French CPC 6128 (the first one a CRTC 1 1985 motherboard, and the second a CRTC 4 Pre ASIC 1988 motherboard).
So without the German CPC shielding.
For my part, I have no perturbation or noise in the speaker.
The problem therefore may not come from the CPC directly, nor from the M4 Board.

Maybe look at some elements of the environment? Position of the WiFi router, antennas, distance from equipment, frequency ranges of WiFi channels (test others?), presence of repeaters, etc.

[GUNHED]

With the !WIFI,0 command you can switch the Wi-Fi off, then there shall be silence!

Alternative get a German CPC6128, the Wi-Fi based disturbances shall be reduced.

More shielding on a german CPC ?

Yes, it has a big metal shield inside. That was the law back the day. So RTTY / radio wave communication is fine with the 6128.

[steph072]

I think I will definitely give up my M4 board. The CPC also crashes from time to time while transfering file to the SD card.

[GUNHED]

I think I will definitely give up my M4 board. The CPC also crashes from time to time while transfering file to the SD card.

To me it sounds like a too weak PSU. Please measure the Volts, they shall be higher than 4,7 at least.

But if you want to sell it... I take it - it's a great piece of work. 

[HAL6128]

Did you attached an external PSU to the M4 board or do you use the cpc internal power supply from the expansion board?

[steph072]

Hello,

I use the power supplied by CPC. No external power.
Do you think it could improve the situation ?

[steph072]

One additional information: I have got a gotek inside the CPC, not the genuine FDD.
It also 5V and need some power even it's not working.

[HAL6128]

Yes, it's recommended. Especially if you use an expansion board where you can plug different board in parallel.
You can use a regular 5V power charger for smart phones with an micro(?) USB. Just switch the jumper in the right position.
By the way, even with a regular CPC with centronics (german version) and metal shield inside EMI perturbations are really high. Just place an old FM radio aside and you will always here "him" (crumpy old bastard).

[steph072]

OK. Thank you. 
The only card connected is the M4.
I will make a try next week with a smartphone power supply and give you feedback.

[poulette73]

HAL6128 is right, it's advisable to provide an external power supply (5V 3A recommended).

However, in my case, I have no external power supply, and several cards on the Mother X4.
And no disturbance sound with Wifi.

And to go further, I have the example below with my 2 CPCs switched on simultaneously, each equipped with a Mother X4, using the internal power supply of each CPC.

The 1st CPC 6128 CRTC 1 with Gotek external drive, Maxduino, and a Mother X4 with USIfAC II+FlashGordon romboard+Nova RTC.
The 2nd CPC 6128 CRTC 4 fitted with a Mother X4 with M4 Board+CPCSixrom romboard+1 MB memory expansion.

And still no sound disturbance with Wifi and Amstrad speakers.
That's why I wonder if the problem might not be elsewhere.

[steph072]

Thank for additional information.
I will try next week with an external power supply for the M4 Board. Perhaps my internal gotek needs to much power and at the end the system turns instable while copying files to the M4 card.
If that's not the reason....then could it be possible that a LTE routeur would be too close to the CPC?

[d_kef]

And to go further, I have the example below with my 2 CPCs switched on simultaneously, each equipped with a Mother X4, using the internal power supply of each CPC.

What internal power supply???
You mean that you have 2xCTM644 monitors or 2xMP-1/2 under the desk that feed power to your CPCs?

d_kef

[poulette73]

And to go further, I have the example below with my 2 CPCs switched on simultaneously, each equipped with a Mother X4, using the internal power supply of each CPC.

What internal power supply???
You mean that you have 2xCTM644 monitors or 2xMP-1/2 under the desk that feed power to your CPCs?
d_kef

Not at all, I don't have any CTM-644 monitor or Amstrad MP-1 module.

Just a single 15" TV LG Brand, with stereo speakers.

Each CPC 6128 is connected in SCART with this cable (x2) : https://www.ebay.com/itm/320751238369
Each CPC 6128 is powered by this transformer (x2) : https://www.ebay.com/itm/324218253955

And with a SCART switch, I swap the display of one or the other of the CPCs by pressing a button. 👍

Sorry for this off-topic, let's get back to the speaker disturbance problem concerning @steph072 😉

[SerErris]

So if you do power your 6128 with a powerfull external power supply (not the original Monitors) than you may have enough power to stable power any external device. However the Monitor included Power Supply does not deliver a lot of current, so it may be to weak to power the M4 (stable).

[steph072]

Hello Everyone,

I confirm that the troubles at the CPC remain with external power supply. Some bytes at the screen are being modified during wireless data transfer, as an example.
Perhaps my Wifi router is too close to the CPC (1m with a wall in between). But as my flat is no huge, installing the CPC elsewhere will be complicated.

If some is interested, please make me an offer for the board. I sell it. 

My CPC is working great with a flashfloppy and I will keep it like that.

[pelrun]

If there's corruption, it's because there's too much voltage drop when the M4 is pulling higher currents. A "more powerful" (as in current limit) PSU won't help, you need a slightly higher voltage (5.1-5.4v) input to give the extra headroom needed.

The Raspberry Pi had a similar problem with most of their models, which is why they started selling 5.1v PSUs; hacking one of those up for my 6128 is what finally solved all the M4 problems I'd been having up to that point.

[steph072]

If there's corruption, it's because there's too much voltage drop when the M4 is pulling higher currents. A "more powerful" (as in current limit) PSU won't help, you need a slightly higher voltage (5.1-5.4v) input to give the extra headroom needed.

The Raspberry Pi had a similar problem with most of their models, which is why they started selling 5.1v PSUs; hacking one of those up for my 6128 is what finally solved all the M4 problems I'd been having up to that point.

Thank you for the explanation....at the end I understand that a device that should make life easier, makes it more difficult. I'm very disappointed about such complexity. I'm a CPC-Hardliner and I spend too much time with such workaround issues, according to my taste.

[HAL6128]

Don't sell your M4 board. It's a great device. The CPC is an old machine and maybe - therefore - power supply and routing is not in the condition as it was 35 years ago. Normally the M4 should work out of the box. With an smartphone psu (5V/2A) mit micro USB attached it works like hell. Try also open your CPC and, if you have further time, measure inside your CPC the contacts - especially the expansion port, for voltage drops? Cleaning?

[Duke]

Thank you for the explanation....at the end I understand that a device that should make life easier, makes it more difficult. I'm very disappointed about such complexity. I'm a CPC-Hardliner and I spend too much time with such workaround issues, according to my taste.

You can pm or email me for a refund and ship the card back to me.

[Duke]

- especially the expansion port, for voltage drops? Cleaning?

Those would be my guesses too, later revisions of M4 board (since 2019) is less picky about voltage (different regulator). The CTM-640/644 powersupply should work fine, as long as contacts are properly cleaned. No need to connect external powersupply.

[pelrun]

I literally soldered directly to my edge connector to try and remove it from the equation, with no benefit. Clean contacts, new DC socket in the CPC, external PSU connected to the M4... none of these worked. There's at least a 0.5v drop before reaching the CPC internals, and then you're in the realm of luck as to whether you can operate stably or not.

I eventually opened up my CTM644 and adjusted the voltage to 5.3v after the RPi PSU hack and all my issues went away, even with an MX4 filled with boards and no special effort in getting perfectly clean contacts. When I'm not using the monitor I've got a USB PD cable that's custom set to supply 5.2v as well (requires a USB C powersupply that supports PPS for this.)

YMMV. And people are just going to keep spouting the same "clean the contacts, get a higher rated PSU" line that prevented me from solving the problem for literal years.