Grounding dedicated PSU for SAA7220

[AndrewGM]

Excuse me if this is me being a bit simple but... a short on pin 16 and 17 when it was switched on ?
Do you think you really did that ?

 

[AndrewGM]

...sorry....maybe a solder blob or something did it ?

I fried an ' A ' with that error once - it's something you don't forget.
I now have a magnifying lense to check all important connections to make sure there are no shorts before I switch anything on now.

Fingers crossed it's something simple that you'll spot and rectify - and not a fried chip.

Good luck

Andrew

 

[josha]

I built the mod under the chip so I had quite a lot going on around those pins, I do check my work though - it's the only thing I can think of (yet) that could have upset it, for once I hadn't tweaked anything else at the same time!

I'll double check everything before writing it off!

Thanks, Josh.

 

[simonov]

Remove the TDA1541 chip and check the power supply ratings. If you have a scope check the signals from the digital filter.

 

[josha]

Hi, voltages all look ok, -5v on p26, +5v on p28 and -15v on p15. Waves all look ok as well I think (see attached - filename denotes the pin). To be honest, I'm not entirely sure what I'm looking at here but everything seems present and correct(!).

Out of interest I popped the original non-a in for a test after checking all the voltages and I get no sound at all! This could be a result of me chopping and re-clocking everything though (I'm guessing).

I'm away for a couple of days this week but I'll do some more digging on my return - I'm not giving up on this yet - it sounded fantastic just before it died and I'd love to find out what I've done

Again, thanks for all your help with this, I'd still be putting up with mediocre sound if it wasn't for this forum!

 

[josha]

Hi all,

After some more poking around with the scope it seems the signal present on pin3 above is constant, ie doesn't change when the CDP is 'playing'. However the data out (pin37 on the 7210) does, ie it jumps to the 'eye' pattern when you press play. hmmm - this leads me to think the problem lies in 7220, it's outputting a signal on the data line whether the CDP's playing or not.

Further investigation required!

 

[simonov]

I have no scope at home to test my player. The simple logic shows that some of the internal blocks of the 7220 chip might be dead.

 

[josha]

Well - there we go, by messing around with something unrelated I managed to upset the SAA7220, who'd have thought it?

So....good opportunity to try NOS (no choice really, I haven't got a spare 7220!), it is very dead and won't even mute so I get a jump when playing the first tracks but I can live with that until I figure something out, it plays ok otherwise. (The 7220 is essentially out of the circuit now).

I also had a very distorted sound until I realised that the bit clock was still running at OS speed(!), it's now running at /4 and seems happy enough.

Too early to tell (and too long since I last heard the player) to decide if I prefer NOS, all I know is the player sounds very detailed and refined, there's not quite as much gain as I'd like from the output stage but apart from that - very happy!!!

ahh - I just found out the pause just makes it jump, no mute might get annoying after all!