Sakhr AX-150 cartridge switches

Par pgimeno

Master (245)

Portrait de pgimeno

06-04-2020, 01:52

I recently bought an AX-150 on eBay. When I first tested it, I felt ripped. The vendor said it was in, literally, "VERY GOOD CONDITION"; however three keys (both shifts and the graph key) are broken, the space bar was stuck and it was resetting or getting hung after a short time.

But I got it because of its unique VDP (the YM2220; I found no other MSX model in eBay with that VDP type), and the customs fee was expensive and painful, so returning it was not an option.

Therefore I set up to fix what I could. Currently the keys are not a big problem; you can still press them even broken. The space bar could be fixed just by snapping the leveraging wire (I mean the one that helps the space bar move as a block even if you press on one side) back into its place; it appears that this wire was shorting the key and that caused the space bar to be stuck.

Then the main issue remaining was the resets. The power led fluctuated and when that happened, it was accompanied by noise in the image and audio, so it really appeared like a faulty contact of something. The problem was locating the cause of this faulty contact.

The obvious suspect was the power unit, which is in a separate board. After spraying a lot of parts with multi-purpose lubricant (I use that to fix faulty contact problems, works like a charm in most cases), nothing seemed to do anything. Moving cables and connectors didn't help.

But then during one of the fluctuations, I noticed some noise coming from an area far away from the power unit, near the cartridge slots, and then noticed that there is a switch in each that activates while a cartridge is inserted. I pushed the switch and the computer (and the power led) turned off! I released it and it turned on again. It appears that they are a protection against inserting a cartridge with the computer on, but in this case the cure appears to be worse than the disease.

Moving them a bit confirmed them as suspect, so it appeared that I had found the culprits. As it turned out, BOTH were causing this issue. It was severely reduced when I inserted the MFR cartridge in the first slot, so it appears that one was failing less than the other.

They are normally closed switches. I sprayed them with a lot of lubricant, but in this case it didn't turn out so well as it usually does. Not sure if I didn't manage to make the oil reach the contacts or what. An ohmeter revealed that the problem was these two little guys unequivocally, as the ohms measurement fluctuated all the time while they were closed, and went to infinity (as expected) when open.

My fix was simply to disable them by shorting the contacts. I haven't had any further problems since. I don't have a protection against inserting a cartridge with the computer on, but that's true for all other models I possess anyway (currently 6 total).

So I hope this serves as a guidance to anyone possibly having this issue.

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Par Alexey

Guardian (2892)

Portrait de Alexey

06-04-2020, 10:43

There's a solution to replace the switches in Yamaha:

http://rbsc.su/en/other_projects/#0107_Replacing_microswitch...

Par pgimeno

Master (245)

Portrait de pgimeno

06-04-2020, 12:31

Oh cool! Thanks, I didn't know it was such a common problem. It looked common judging by the fact that both failed, which suggested that it was due to age.

Par DesertPanther

Supporter (3)

Portrait de DesertPanther

26-07-2020, 06:10

Don't forget to give that eBay seller a bad rating and review.

Par Gloriou

Master (181)

Portrait de Gloriou

05-09-2020, 16:20

I'm sorry that happened to you!
I think I know that person, I believe he is from Egypt. I got one myself with three broken keys, but mine was from another seller in my country (Saudi Arabia). But I think this seller got it from Egypt so same thing Smile

Buying an MSX is risky unless you know that the seller really knows how to protect it Big smile