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Taito Space Invaders L shaped Taito upright


tevo

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Hi guys,

 

I have a Taito Space Invaders upright with the Taito (Midway) L shaped board set up as pictured.

 

I got it working after sitting for 36 years sitting in the original operators shed.

New main fuses and it fired up.

 

But there is no sound.

Adjusting the main volume pot does nothing.

 

Last I checked the voltages they were all good going into the board and the speaker also had voltage going to it.

 

Online there’s Midway board repair logs for sound issues but next to no Taito L shaped ones.

Are the Taito L shaped boards (which I know are Midway) exactly the same?

 

Just need some pointers to check more potential areas causing the issue and hopefully fix.93D9238D-910C-43AC-A787-141C859EEB3C.jpg

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You have a Midway PCB (though it has Taito stickers it's made in USA), they are different (but generally the same) to a 'Taito' (made in Japan) PCB which has an edge connector instead of a pin type connectors like on your PCB.

Do you get a 'pop' from the speaker when the board boots up??

The first thing I'd suggest is put your finger across the pins at the back of the LM377 (chip with the heatsink) and see if you're getting a buzzing noise, if not the amp probably isn't working.

Do you have 8 ohms across the speaker?

If you get some noise then work backwards, check the LM3900 below the volume pot as well as the pot and caps around them (circled in red).

The LM3900's on your board are socketed so try swapping the one near the pot with one from another location if you have no way of testing it, they're also available from Jaycar.

The caps are cheap to replace for testing purposes if you don't have a component tester.

 

Vo9cm5N.jpg

 

Also check continuity from the grey pins in the image below to the speaker.

Check the amp has voltage at the two pins next to the speaker wires or at the 10uF electrolytic cap (red rectangle).

 

am742t1.jpg

Edited by Kaizen
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My multimeter fell apart the other night testing the ohms.

Time for a decent one.

 

No pop when it turns on.

First thing done was replaced the LM3900’s for each sound effect.

Will check back with the other findings.

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Common Failure items:

* The 10uf Tantalum cap under the audio amp heat sink will short, blowing a fuse on the 12v line.

* The LM3900s die off en masse. Grab a handful and expect to replace most of them.

 

I've also had one board come in where the solder looked perfect but yet you could slide the pins of 2 of the poly film caps in and out of the board at will. Resoldering those fixed missing audio.

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I got another multimeter so keen to try to get the sound working on this.

Tested the following:

 

Do you get a 'pop' from the speaker when the board boots up??

No pop at start up.

 

The first thing I'd suggest is put your finger across the pins at the back of the LM377 (chip with the heatsink) and see if you're getting a buzzing noise, if not the amp probably isn't working.

No buzz with finger.

 

Do you have 8 ohms across the speaker?

Yes got 8 ohms at speaker.

SI ohms.jpg

 

Also check continuity from the grey pins in the image below to the speaker.

Yes have continuity of those 2 pins.

SI continuity.jpg

 

Check the amp has voltage at the two pins next to the speaker wires or at the 10uF electrolytic cap (red rectangle).

No voltage for the amp.

What's required to fix from here if it is that in particular?

SI amp voltage.jpg

 

- - - Updated - - -

 

Common Failure items:

* The 10uf Tantalum cap under the audio amp heat sink will short, blowing a fuse on the 12v line.

* The LM3900s die off en masse. Grab a handful and expect to replace most of them.

 

I've also had one board come in where the solder looked perfect but yet you could slide the pins of 2 of the poly film caps in and out of the board at will. Resoldering those fixed missing audio.

 

Thanks. I checked the caps. They all look good.

10uf Tantalum cap - Haven't tried replacing this just yet.

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No fuses blown that I know of.

When I first got it and powered it up it had a blown main fuse which at the time also caused a garbled graphics screen. I replaced 3 of the main 4 fuses at 2A, 3A, 1A, 5A with new ones and had the game playing with no sound.

 

Are there any other fuses hiding away?

 

Just checked the 10uf Tantalum cap for continuity and it is OK.

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It's rare for the amp ICs to go out on those old boards. Your culprit is more likely the LM3900 ICs. They fail like crazy on those old boards. Replace the one connected to the volume control first.

 

But, if you don't have 12v to the amp chip then that's for sure the issue. If the 10uf Tantalum cap isn't shorted and the fuse isn't blown - and yet you still don't have 12v to the chip then you'll need to check the connections, harness, and even the power supply itself.

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An update. I thought the fuses were fine but it is indeed blowing the 2A fuse when replaced on start up each time.

Which is a good thing I guess.

Will replace the tantalum cap and replace lm3900’s again as have spares.

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I gave Joey at Jomac a few jobs including checking out those caps.

3 were shorted.

I put it back in the cab, turned it on, heard an encouraging pop from the speaker and the sound fired up.

 

All sounds working except base explosion and a higher than normal pitch for the missle.

I’m suspecting replacing the one 4006 may fix both remaining sound issues.

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Good news.

The 4006 chip swap did indeed fix the high pitched missile noise and the missing base explosion is now present.

 

Another Taito Space Invaders saved and fixed from dead to fully working.

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