What the reason was or is, hopefully Tecnobytes can figure out, because if it is an error in assembling the slot-expander, a human error, then they can spot it otherwise more people would have an issue. Maybe there isn't, and the fuse was eol.
Keep that MSX alive ! 
I have been using the Tecnobytes slotexapander with external power supply on a FSA1-GT, no problems so far. You got me death scared about damaging my MSX though 
I have been using the Tecnobytes slotexapander with external power supply on a FSA1-GT, no problems so far. You got me death scared about damaging my MSX though
It could just be that fuse dying on him by pure accident bad luck
Hello Tecnobyters.
I will "paste" the emails that we had sent since the problem began...
Let's see..
Fisrt Message from Alex:
BEGIN ----------------------------------
Hello, I received your slotexpander, been streaming the unpacking last night and discovered several issues.
Volume Panasonic is too low in slotexpander,
Philips Music Module doesn't work properly, demo is on adhd and which use MSX Audio crash even with the module inserted.
This is not happening without the slotexpander.
So now I have a product which is not fully compatible with all my cartridges.
Setup
Philips NMS8245 MSX2
Got a Sparrow Soft / Stichting Green 1Mb Memory mapper,
Which is inserted on top of MSX.
Slotexpander cartridge in back of MSX.
Slotexpander is filled with
MCWF Fmpac ( boosted audio so at least some MSX Music )
F1 Spirit for SCC
Nowind USB Interface.
4th slot supposedly the Music Module but gives to many issues in slot expander.
Hope there are solutions for this. since I'm not happy with the results obviously and several viewers have also seen the issues caused by the product since it was a live stream.
Greeting,
Alex / Hydragon
END -----------------------------
First Reply from Tecnobytes:
BEGIN -------------
Hi Alex!
Do not worry. Let's solve all your issues.
Let's do some testing here with a similar setup, okay?
Give us a few days, please.
Thanks for your comments and sorry for the inconvenience.
Kind regards,
Tecnobytes Brasil
END ---------------
Next Message from Alex
BEGIN -----------------
I can give an update correct order is front to end:
FMPac, SCC ( F1 Spirit ), Philips Music module, and as last slot, Nowind ( very important!! )
If Nowind is not in back slot and before Music Module, the Music Module, will act in crazy and software even crashes.
Slotexpander is in back slot of MSX.
Memory mapper in top slot of MSX
MSX model: Philips NMS8245.
This currently seems to work, now I need to find out how to surpress the feedback/background noise from television.
END --------------------
REPLY FROM TECNOBYTES:
BEGIN ----------
Ok Alex!
Thank you for the details!
If you have any more comments, please send us!
Kind regards,
Tecnobytes Brasil
END ------------
ANOTHER TECNOBYTES MESSAGE:
BEGIN ----
Alex,
are you using the MSX Music Module software (or other)?
Thank you!
END---
MESSAGE FROM ALEX:
BEGIN ----
Music Module now works fine.
I can even go on Twitch for a live stream, after I´ve went to the store, so we can replicate the issues.
For now the setup works, just need to find out how to achieve background noise surpression, to get audio clearer in general.
END---
ANOTHER MESSAGE FROM ALEX:
BEGIN ---
OK, here´s the first issue, I would love to use my original FMPac, but for some reason, the volume is much lower when using the slotexpander.
Tested the cartridge directly in primary slot, perfect volume, also in backslot, perfect volume, once inserted in Slotexpander, volume decreases with 50%.
Same is happening with the Philips Music Module.
This is of course quite dissapointing. =( How can this be resolved.
I spended 235 euro, for the expander. Which is a lot of money and now i can't use my hardware properly 
END---
REPLY FROM TECNOBYTES:
BEGIN ---
Alex
Can you tell me what is your paypal account (which you used to purchase the slot expander) and the transaction number?
Let's see how we can refund you and resolve the issue.
Regards,
Tecnobytes Brasil
END ---
MESSAGE FROM ALEX:
BEGIN ---
Order was done through Mika Tähti, which will make it a threeway conversation.
Keep me updated. My own paypal is: xxxxxx (i erased to not display information)
Greetings,
Alex Koedooder.
Additional update, my MSX2 got damaged after 3 days of using the slotexpander, shared the info over videocall with Mika, he was stunned. My FMPacs and Philips Music Module don't output over TV anymore, Software does run, and chips are recognised just no audio anymore over the 8245, PSG, SCC still work fine, but that's obviously not good enough. Tested external output of Philips Music Module and also tested that in my 8250, fortunately a positive result.
END---------
ANOTHER MESSAGE FROM ALEX IN THE NEXT DAY
BEGIN ---
Any updates on this matter? You have my emailaddress for paypal. which is again XXXXXX
Since my MSX also got damaged by the product, someone is gonna fix it, but ey that costs me also 150 euro.
So thus far, the slotexpander putted me in a bad mood, still not seeing a result of a solution. Broke my MSX2. With total costs now at 385,= euro ( what has been spend for the expander, + the repairs that has to be done for the MSX2. ).
Since MSX-Audio and MSX Music aren't properly outputted over the TV anymore. They do work ina diff model, but I'm obviously not gonna hook that model up with the slotexpander as well.
END---
REPLAY FROM TECNOBYTES:
BEGIN ----
Alex
There is no way for the Expander Slot to perform any kind of incorrect function on any MSX MACHINE that causes this type of problem. He's protected. Or you used it improperly.
We sold almost 70 units without any kind of problem.
I suggest you to find the "seller" and ask him to solve your problem or send your money back (and that amount you are asking for is much higher than the value of the Expander ...). We can not do this for you because you did not buy the item directly from us. How can we return something that you did not send to us?
Regards,
END----
REPLY FROM ALEX
BEGIN---
Fine, on that note there's one option then, and I'll inform my subscribers and viewers about Tecnobytes and this information.
Because that you even mention I've used it improperly is a joke.
The fact that if you insert an SCC there's a high pitched sound coming from the TV, ensures there's something going on, which makes it obvious it has never been properly tested!
When this news hits the MSX scene, more people will perform the same tests and you'll get even more complaints and mail coming your way.
I tried to be nice and we could look for a correct solution, but this makes no sense at all.
Mika has seen also seen the damage that has been done.
And improper usage?? All it had in the slotexpander, was a Nowind, FMPac, and SCC, and since volume is unbalanced, and fact volume even gets lower in slot expander is bad behaviour at all means. Even had slotexpander hooked up to it's own power.
This states that I received a malfunctioning product created by Tecnobytes, which can do harm to MSX computers, but you are onviously ignoring the fact that something is wrong.
Fine let's go the public way, which will also become bad publicity for you. Because the message you just send me is just a bunch of nonsense and not a workable solution.
END----
REPLY FROM TECNOBYTES:
BEGIN----
You may not know it, but the SCC cartridges have lower *** impedance, which causes a decrease in power and consequently in volume. It is not a defect.
Feel free to act as you want. We are fully aware of what we do. We have more than 30 years of MSX.
Do you buy something from someone else, pay that other person a higher amount than what we charge, then do you think you have a problem and come to charge from us? I did not understand your logic. How are we going to pay you for something if you have not paid us ???
Return to your supplier, ask them to return what was paid. He can send the expander back if he wants and we'll give him back the amount he paid. Not, you...
Regards,
Tecnobytes Brasil
END---
*** CORRECTED IN THE NEXT LAST MESSAGE WITHOUT RESPONSE
Well, it looks like the story was not quite like it was told.
We do not refuse to answer or help. But we can not return a value of something that has not been paid to us.
Another point of common sense. A 30 year old MSX, turning it on and off, with a lot of things on it ... what are his chances of having a problem ???
And even more ... charge 150 EUROS for a repair that does not even know what it was, it seems at least act in a bad faith.
Sorry for the long message, but we can not continue with this kind of attitude. We are few and if we do not help each other, we will be less.
Greetings,
Tecnobytes Brasil.