Defender sound board redux

Kalamath

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History: this machine has never made game sounds for me. Speaker pop/thump on startup. I rebuilt the sound board with new caps, new PIA chips (IC9 AND IC10), and a new crystal. I've also tried putting in the sound board from my Robotron (with the Defender ROM chip) but nothing happens. The jumper from the ROM board is solid, and I checked for pulse during sound test on both sides of the cable, consistent results. I've also tested with 2 separate ROM boards, same results. Speaker tested out of the cab, works fine, and wiring is good (close to 7ohm at the board).

Voltages on the sound board are T1= 10.9, T2= -14, T4= 4.92, T3 (ground) has continuity.

When I run the sound test and start tracing the signal, I start at the inputs on J3. Lines 6 & 8 do not pulse, but stay on High. 2,3,4,5,7 all pulse.

Looking at IC5 (where the signals go through on their way to the PIA IC10), most of the inputs from J3 pulse, except IC5-11 which is dead. No signal H or L. Oddly enough IC5-12 pulses. I checked this like 20 times cause the logic sheet shows 11->12. IC5-6/7 both stay H.

Looking at IC10 inputs, they pulse, except for IC10-18 (from J3-6) which stays H I think, and IC10-17 (from J3-8) which is DEAD...no signal H or L.

Looking at IC13-5 to 12, no pulsing. If I poke at IC13-9 I hear static from the speaker, and can adjust the volume of said static with the volume pot.

So, whats really going on here? Are the input from the ROM boards correct, with J3-6 & 8 NOT pulsing? Is IC5 bad? Could the op amp be bad, even though the speaker pops on startup and makes static when you poke IC13-9?
 
It looks like the 6821 PIA chip is dead from your symptoms. That is IC10, the big chip. If you are lucky, somebody has already socketed it for you, if not, they are a pain to desolder. Be very careful when removing these suckers as it is very easy to lift traces.

THe audio amp is probably not bad if you can adjust the volume of the static. You need to get the input lines to the A/D chip (IC13) pulsing and the next upstream chip is the PIA.

ken
 
You really think so Ken? These are brand new IC9 and IC10's in there, from Bob Roberts. I suppose it could have been DOA, but damn...


And yeah, I put in a socket, hehe.
 
My Stargate's sound board was on its way out, and it too made a big POP at power-on. Replacing the TDA2002 amplifier made everything right again. It shouldnt "POP" on startup.
 
My Stargate's sound board was on its way out, and it too made a big POP at power-on. Replacing the TDA2002 amplifier made everything right again. It shouldnt "POP" on startup.

really? mine does that, I thought it was normal though. unless you're talking a serious pop. my speaker actually has like holes in it too.. though I don't think that has much bearing on the situation at hand.
 
really? mine does that, I thought it was normal though. unless you're talking a serious pop. my speaker actually has like holes in it too.. though I don't think that has much bearing on the situation at hand.

Well in the context of popping and having no sound afterwards, I think it does. Mine gave a large "FWUPP" when you hit the switch (dunno how else to describe it) and from that point on, all the sounds were distorted/clipped, like someone turned an equalizer up past its limits. Replacing the amplifier resulted in crystal clear sound and a silent power-on.
 
oh haha. well I can tell you, ancient speaker and all, the sound on my Defender hits HARD. so I don't think I have any issues there.
 
Update:

I've come back to this project after some time off. I replaced IC5, swapped in another brand new PIA (IC10) and a known working IC9. Still no sound. So...something between IC10 and IC13 is busted...I have to find out what. Studying the 8224 logic diagram, but I cant quite wrap my head around the data sheet for the 6821 just yet.

I really need something though, for piece of mind, if one of you would be so kind. Please someone, put a Defender into sound check and tell me if J3 (plug from the ROM board to the Sound board) pulses on pins 6 and 8? Mine does NOT pulse, and I'm left not knowing if THAT is my problem, and I'm wasting time running around checking the sound board itself. I also need to know if pin17 on IC10 (the PIA) is supposed to pulse if J3-8 does. Help me Obi-Wan...
 
Yep. Had a new one so threw it in there, even though it didn't make sense to me, but I didn't have anything else to try at the time. Wasn't the amp. It has to be something past the PIA but before the amp.

Pin17 on my PIA is dead (it's NOT the PIA!) so maybe something in between J3-8 and IC10-17 is kaput? Like I keep saying though, I don't know if J3-6 and -8 are right, since they stay high in sound test and don't pulse. Hard to figure out how stuff works if the inputs aren't documented.
 
Pin 17 gors to jumpers w12 and w13. It is going to be floating so ignore this.

You do have the dip switches off don't you? They route the sound through the expansion header (for speech) if they are turned on.

If you look on IC 13 with your logic probe, you should see pins 5 - 12 pulsing when sounds should be playing. Those are the Digital lines. If you see those pulsing but no sound, then it is either Q2 or chip 13 (the D/A converter).

If the output from the PIA is not pulsing, then you need to check the inputs, pins 10-15 & pin 18 on the PIA. These match up to the input lines. Pin 18 is the handshake to let the PIA know that there is a signal to look at. It comes from chip 6. The other lines go through the inverters IC5 & 7.

So if you are seeing activity on the connector lines and not at the PIA, then test or replace IC5.

That will work the signal both directions from the PIA.

ken
 
I'm on to something (I know this is coming slowly...)

1. Looking at IC9 (the MPU) I have clock, but NO clock on IC10 (the PIA) - recap says Clock ckt fault
2. IC9 pin36 is LOW - recap says that's a Reset ckt fault
3. IC9 pin6 is LOW - recap says Debounce ckt fault (no idea what this is...)
4. Most pins on IC2 are pulsing - recap says to replace IC2 & check the other address ICs
5. .....

I'm of the mind that something really bad happened to this board, and every IC on it that I haven't already replaced is messed up.

Ken, I replaced IC5 already. I had definitely figured out that was bad.

Everything is fine up TO the PIA but then it goes bad...it's NOT the PIA though, I have three new ones on hand that I've checked with.

Regarding the DIP switches...I've tested with them in both positions. Mine does not say ON and OFF: it just says OPEN. Open = off? I don't know but that's my assumption.
 
I just tested both IC9 MPUs (6808 and a 6802) IN the Defender cab, but with a Robotron sound board. I didn't connect the ROM board, just used self test switch. Test plays sound with both MPUs, and pin5 (VMA) is High.

Next, I tested both MPUs in the Defender sound board, same setup. Both MPUs test LOW on pin5 indicating a MPU fault. WTF? So I remove power, take the ROM chip out, turn on and check the address lines: pulsing. Reverse the process, and noticed that the address lines are still pulsing UNTIL I hit the test switch, and then they STOP, indicating an address line chip fault.

This, again, points to IC 2, 3, 10, 11. IC10 is ruled out, IC2 is definitely bad (two tests now point to it) and possibly IC3 and IC11 (ram). Time to order some parts.

ps. Open = off on the dip switch. =)
 
Off = Open is the correct setting for both switches. I always ask now as I had someone ship me their sound board and that was all it was. So I don't second guess about that any more.

Sorry if you have mentioned this before, but have you checked the sound ROM in a ROM burner? Some of your symptoms sound like a bad ROM.

ken
 
No...I ordered one for the Space Duel project but it's not here yet. Hopefully sometime today. I definitely mean to check the ROMs (I have 2).

Since the ICs are cheap, I ordered up a couple of each for the rest of the board. I don't mean to replace them all at once though. I'll continue this process of learning how it works, and what's definitely bad, before replacing anything.

Appreciate the feedback you've been lending.
 
Appreciate the feedback you've been lending.

Me too. :)

I've got some spare Defender parts not in use. I kind of want to get them running so I can sell them or sell them so someone can get them running or trade them for something that works. But reading this thread is helping me too... at least I can follow it and throw my logic probe on the boards according to what you guys have suggested--so thanks.
 
I replaced the ICs that were acting wonky (so, it's running all new ICs at this point), but now I'm getting a reset issue. Namely, the MPU pin36 is low, which the Williams recap says is a reset ckt fault, but then they don't describe the reset circuit at all. Just says "repair it" - gee thanks! I replaced Q3 & Q4 just in case one of those was bad, but now I'm just guessing.

I have the schematics, I can see the components, but can someone describe how this circuit works please?

edit: in particular...I (think I...) understand the relationship between the PIA reset line (pin34) and MPU reset (pin40)...both of which are HIGH, but how does MPU pin36 come into play, and why does a LOW there indicate a reset circuit fault, according to the Williams Recap manual? I'm definitely missing theory somewhere & need clarification.
 
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