Williams Defender sound board any sound

[jammatt]

Hello, im tryng to fix my williams defender sound board
I dont have any sound, i already tested CPU e ROM with onether working sound board.
Voltage are ok, fuses are ok, also tried to change the TDA but nothing changed

Please help
Thanks

Matt

 

[philmurr]

What sound do you get if you press the test button on the sound board?

 

[jammatt]

Hello, i dont have any sound if i press the test button.
Thanks

 

[philmurr]

It sounds like it could be something to do with either CPU / memory / PIA / DAC circuitry

Edit: forgot to mention the PIA
philmurr2018-05-23 20:47:47

 

[jammatt]

thanks Phil,
CPU its ok, i tested on another sound board.
Is there any IC that i can try to change or transistors?
I dont have too much experience, but if you can drive me, i can try it.

Thanks
Matt

 

[philmurr]

What test kit do you have?

Can you check the inputs to the DAC / outputs from the PIA with a logic probe and see if they’re changing?

Check and see if address and data lines at the CPU are changing?

Check if NMI is pulled low when pressing reset button

Check /CS inputs at ROM and RAM

 

[jammatt]

Ciao Phil, thanks for replying me.
I have only a logic probe

Matt

 

[philmurr]

I have only a logic probe

Ok Matt that’s all you need for the above tests. Let me know what you find.

 

[jammatt]

Ok Phil, i was looking at the schematocs.
I think that the DAC should be IC13 and the IPA IC10.
So about 1 point:
"Can you check the inputs to the DAC / outputs from the PIA with a logic probe and see if they’re changing?"

I need to check pin 13 from IC13 and pin from 5 to 12?
Sorry but im at a really basic level

Thanks

 

[jammatt]

Ok, i think i got the first 3 point.
Let you know next week when i'll be back at home.

Thanks so much
Matt

 

[philmurr]

Yes check 5-12 on IC13 (after you’ve pressed the test button so it should be trying to produce sounds)

Also before you do any of the above checks, make sure the volume control is connected or you’ll get no sound at all...

 

[jammatt]

Thanks, let you know

 

[chadsarcade]

If the transistor by the DAC fails you also get no sound.

Easy test for it it press the test button, and put a finger over the transistor solder pads on the bottom of the board. If you hear very faint sound, it's probably bad.

Or course, this assumes the CPU/RAM/PIA/ROM are all ok.

Don't overlook the obvious with the ROM either, make sure the board is strapped for a Defender ROM/2716 and not a Robotron style 2532. They do sometimes get swapped.

 

[jammatt]

Thanks Chad, i'll do this test too.
Q2 tansistor?

 

[jammatt]

Hey guys, did some test.
- About DAC outputs from the PIA i did a video HERE
- "Check if NMI is pulled low when pressing reset button". If is 6808 IC9 PIN6, yes is pulled low.
- "Check and see if address and data lines at the CPU are changing?"
Are this one: 6808 IC9
ADDRESS PIN 22/25 - PIN 9/20
DATA BUS PIN 26/33

@chads cant hear any faint sound on Q2 transistor

Thanks.
Wating for you

 

[jammatt]

Hi,
any ideas

Thanks

 

[chadsarcade]

Check the reset pin on the CPU

Most of the time I've found either the 6810 ram is faulty or the 6821 PIA is bad.