Defender Sound Issue

[Superully]

I capkitted the monitor on my defender machine and when i put everything back together again, the sound was gone
i didn't remove any wires, the only thing i DID remove was the monitor chassis - so this can't be a loose connector.

here's a picture of the sound board installed (i've read that there are different versions, so perhaps this helps):

as i've said, i don't have any sounds at all - turning the volume knob on the right (circled in red) didn't change that, BUT what i can hear when i set the volume to maximum and press the test switch (circled in yellow, at least i've read that this is a test switch, hopefully that's not a voltage regulator ) are faint sounds coming from the sound chip itself - so this seems to be working.

please check out this short video i filmed - starting at roughly four seconds in (when i turned up the volume to the max) you can hear those sounds (you have to turn up the volume on your speakers a little bit to hear it clearer).

enough said, here are my questions:
- what's the first thing you would check / do?
- could it be the speaker itself (and how do i check its function)?

note: i'm not an electro geek, so go slow on me please

 

[WindDrake]

I'll throw in my 0.02, because while I'm not familiar with your particular machine, electronics I do know. However, the schematics for this thing hurts my head. I hate hand-drawn stuff!

First thing I noticed is that something barfed black junk all over your cap stack on the top left corner. The cans don't look ruptured, though. Just junk, I suppose.

If you can hear sound when you crank the volume pot all the way up, there's atleast preamplified sound being generated.

Before we do anything, we'll check the volume control potentiometer. On the other version of this board, it's a 5k Audio-Taper Potentiometer.. The schematic I have here does not list your version's pot . So we'll continue assuming it's a 5k pot. It should read 5000 Ohms from pin 1 to pin 3. When you center the pot, read from pin 1 to pin 2. Write the total down. Then read from pin 2 to pin 3. Add that number to the previous total. It should be 5k, or thereabout. If it's way the hell off, replace the pot.

Still not working?

We'll start at the amplifier, since we know the thing is making noise.

Your fuses are obviously good. They look ok, and considering they are hooked up to the hot/neutral sides of the Bridge Rectifier, the thing would be barfing if they were blown.

Speakers are next. Disconnect the quick-connects from your speakers, and measure across the poles using a Multimeter in Resistance Mode. You should see 8 Ohms, or thereabouts.

Assuming that's good, your speakers are hooked to J2, Pins 1-4. You should get continuity (Beep Mode on your Meter, for lack of better words) from the quick connects to those pins inside the J2 connector. (Page 32 of the Defender Manual PDF on KLOV's manual Page.)

Judging by the schematic, the unit is Mono Sound, and the speakers are in.. Parallel. Which makes sense as the Amp chip is designed for 4 Ohm out (Two 8 Ohm Speakers in Parallel with eachother = 4 Ohms total resistance.)

Still good? On to IC1 (TDA2002 8w Power Amp from Fairchild Semiconductor).

http://www.datasheetcatalog.org/datasheets/400/378176_DS.pdf

Check pin 5, that's your amp's power-input pin. Admittedly, the schematic here is pretty old, so I can't tell what the source is supposed to be. The Datasheet lists 8-18V supply range, so I can only assume (by convention) that it's supposed to be +12v.

If the Amp has power, I would check the outputs. Using a 4 Ohm speaker you have laying around, you can use probes (like you'd see on your multimeter) to probe against pin 3+4 (Pin 3 is Ground, pin 4 is out) and listen for sound.

That's all for now. Take it slow, and be careful!

 

[Superully]

cool, thx a lot for the looong writeup. i'll probably have more questions as i'm moving along, but for now there's some stuff i can do. however, it'll have to wait till tomorrow, already too late for repair stuff over here in germany

i'll keep you posted, but for now: THX AGAIN!!!

 

[Superully]

update! follow the instructions on what to do today:

- checked the "junked" capacitors on the upper left corner and came to the conclusion that they are indeed ok! -> CHECK!
- measures the volume pot, results were convincing! -> CHECK!
- removed the spealer, measures it with a multimeter and tested it with a 9V battery! -> CHECK
- probed the wires from the speaker to the speaker board for continuity ("beep test"): red wire = BEEP, black wire = NOTHING!!! re-checked the black wire again and again with the same results. quickly installed a replacement wire for testing purposes and anxiously attached it to the speaker, turned on the game and ...

...

and

...

VOILA!!!

the sounds are back

to be honest, i had never had a "broken wire" before and i never thought it would be as simply as that, but i'm thrilled that it turned out to be an easy (and cheap) fix!

thx a lot for the lenthy writeup again, winddrake, luckily i didn't have to follow it to the end

my defender can now be moved back into the gameroom!

 

[WindDrake]

Awesome! Glad I could help.

 

[Dokert]

The speaker wires run right next to the monitor chassis in those old Williams games, and it is not uncommon to lose the speaker connection when installing a rebuilt chassis.