Atari 800 Computer no Sound

[Porkchop]

I'm trying to get an Atari 800 working and can't get any sound out of it.  Here is what I have tried so far with parts from another working 800:

 

1.  Swapped the Power board which has the RF on it,  No sound

2.  Swapped the Pokey chip, still  No sound

3.  Swapped the CPU board, still  No sound

3.  Swapped the 10k ROM board, still  No sound

 

Does anyone have any suggestions for what I might try next?

[_The Doctor__]

op amp and related parts transistor / coupling cap

[Beeblebrox]

Do you get key clicks from the internal speaker? Assume not. Also what a/v cable are you using to connect to your display? 

 

Are the sockets for pokey checking out in terms of continuity? 

 

Audio pin on the din connector OK? 

 

Generally have you tried gently raising socketed chips out of sockets a fraction and reseting them given the decades they have been sitting in them? 

 

Pcb looking OK in terms of checks for cold solder points and bad traces /vias? 

 

I am wondering too if this is a passive component issue. 

 

 

[Rybags]

I think you'd be wanting to concentrate on the motherboard, from the audio out pin on Pokey then onwards along the path to final output.

 

Internal speaker is prettymuch irrelevant here, there is no commonality other than power.

[Peri Noid]

10 hours ago, Porkchop said:

I'm trying to get an Atari 800 working and can't get any sound out of it.  Here is what I have tried so far with parts from another working 800:

 

1.  Swapped the Power board which has the RF on it,  No sound

2.  Swapped the Pokey chip, still  No sound

3.  Swapped the CPU board, still  No sound

3.  Swapped the 10k ROM board, still  No sound

 

Does anyone have any suggestions for what I might try next?

If the op-amp is fine, I'd suggest checking the connector between the mainboard and PSU board. I had a case, where one of the contacts there just broke.

[Porkchop]

6 hours ago, Beeblebrox said:

Do you get key clicks from the internal speaker? Assume not. Also what a/v cable are you using to connect to your display? 

 

Are the sockets for pokey checking out in terms of continuity? 

 

Audio pin on the din connector OK? 

 

Generally have you tried gently raising socketed chips out of sockets a fraction and reseting them given the decades they have been sitting in them? 

 

Pcb looking OK in terms of checks for cold solder points and bad traces /vias? 

 

I am wondering too if this is a passive component issue. 

 

 

I using the RF to the TV and I know it works fine because I have used that same power board with another main board and have sound.   I also tried a composite cable and same problem no sound.

 

Tried to trace connectivity from both the Pokey end and the power board connector end and things seem to be ok so far.  Looking at the schematic I see that the CA3086 Transistor array is part of the circuit between the Pokey and the power board connector.   I think I will try to replace that next.   The connective between the Pokey and CA3086 seems ok.  

[Mclaneinc]

What does the Atari use (no got schematics local) LM386?

[TGB1718]

1 hour ago, Mclaneinc said:

What does the Atari use (no got schematics local) LM386?

It uses 2 transistors in a transistor array to amplify the sound (A104)

 

[Mclaneinc]

Thank you for that, I wasn't trying to sound like I knew stuff (I've said many times I'm not into electronics theory) but I sold gazillions of those chips when at Maplin, while I didn't know what to do with them, I had most of the spec in my head from the catalogue, and it seemed to be the go-to item when an op amp was needed.

 

Best of luck to the OP..

[_The Doctor__]

if it were a chip, it would have been noted, it's the op amp transistors and their coupling to check as stated.

TGB1718 +1 for posting the schematic