CD104 channel failure - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Uncle Bulgaria · 30th Nov 2020, 6:53 pm

10.6V. 9.9V on pin 2, 0.1V pin 3.

TonyDuell · 30th Nov 2020, 7:05 pm

So 3937 is open-circuit. 3576 is open-circuit. And you still get crazy voltages. The NE5532 is known good. There is a DC feedback path (that 1k8 resistor) from pin 1 to pin 2. Power rails are good at the chip pins.

It's rapidly becoming impossible. We're missing something very obvious

Uncle Bulgaria · 30th Nov 2020, 8:06 pm

Thanks for your help, Tony - it's not just me going mad then! I've redone all the solder points around that part of the board, in case a dry joint hasn't been helping matters.

With the NE5532 unplugged, 1, 2 & 3 are all at about 0.1V and even 6 & 7 have dropped to 0.4V. Perhaps the IC is intermittently faulty, because as you say there's nothing else that could be going wrong!

I'll switch them over again to make sure we're not chasing our tails here...

Ted Kendall · 30th Nov 2020, 9:07 pm

Are there any of those annoying copper rivets on the board?

Uncle Bulgaria · 1st Dec 2020, 1:15 am

It did have the dreaded 'griplets', but I dealt with those some time ago.

Progress: I think the NE5532 was intermittently faulty, and I didn't have it on long enough while connected to the other channel for this to manifest. Perhaps the soldering and de-soldering pushed it over the edge, as it's now reliably reproducing the high voltages. R3576 had gone OC as well. Using the other NE5532 and an axial resistor tacked in place of R3576 results in a legible analogue signal at the L output and reasonable voltages, when connected to either DAC. Unfortunately I haven't any other NE5532s or SMD components so I'll have to wait until I can get hold of some before the possible cure can be tested...

DMcMahon · 1st Dec 2020, 5:05 pm

I am not familiar with these copper rivets/griplets. Googling Griplets describes them as Miniature IDC Connectors (Amphenol), are these the same things as your griplets ?

Uncle Bulgaria · 1st Dec 2020, 5:30 pm

No, they're through-hole links between ground planes on either side of the board. They're labelled 'griplets' on the circuit diagram so the name's stuck. They're famous as the fault on the CD104 and other models, as they cause intermittent ground connections and result in all sorts of bizarre behaviour. The accepted best practice is to unsolder them all and re-make them with a piece of wire through each hole, which is then soldered to the planes on either side of the board.

30th Nov 2020, 6:53 pm	#21
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,333	Re: CD104 channel failure 10.6V. 9.9V on pin 2, 0.1V pin 3.

30th Nov 2020, 7:05 pm	#22
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: CD104 channel failure So 3937 is open-circuit. 3576 is open-circuit. And you still get crazy voltages. The NE5532 is known good. There is a DC feedback path (that 1k8 resistor) from pin 1 to pin 2. Power rails are good at the chip pins. It's rapidly becoming impossible. We're missing something very obvious

30th Nov 2020, 8:06 pm	#23
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,333	Re: CD104 channel failure Thanks for your help, Tony - it's not just me going mad then! I've redone all the solder points around that part of the board, in case a dry joint hasn't been helping matters. With the NE5532 unplugged, 1, 2 & 3 are all at about 0.1V and even 6 & 7 have dropped to 0.4V. Perhaps the IC is intermittently faulty, because as you say there's nothing else that could be going wrong! I'll switch them over again to make sure we're not chasing our tails here...

30th Nov 2020, 9:07 pm	#24
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: CD104 channel failure Are there any of those annoying copper rivets on the board?

1st Dec 2020, 1:15 am	#25
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,333	Re: CD104 channel failure It did have the dreaded 'griplets', but I dealt with those some time ago. Progress: I think the NE5532 was intermittently faulty, and I didn't have it on long enough while connected to the other channel for this to manifest. Perhaps the soldering and de-soldering pushed it over the edge, as it's now reliably reproducing the high voltages. R3576 had gone OC as well. Using the other NE5532 and an axial resistor tacked in place of R3576 results in a legible analogue signal at the L output and reasonable voltages, when connected to either DAC. Unfortunately I haven't any other NE5532s or SMD components so I'll have to wait until I can get hold of some before the possible cure can be tested...

1st Dec 2020, 5:05 pm	#26
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: CD104 channel failure I am not familiar with these copper rivets/griplets. Googling Griplets describes them as Miniature IDC Connectors (Amphenol), are these the same things as your griplets ?

1st Dec 2020, 5:30 pm	#27
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,333	Re: CD104 channel failure No, they're through-hole links between ground planes on either side of the board. They're labelled 'griplets' on the circuit diagram so the name's stuck. They're famous as the fault on the CD104 and other models, as they cause intermittent ground connections and result in all sorts of bizarre behaviour. The accepted best practice is to unsolder them all and re-make them with a piece of wire through each hole, which is then soldered to the planes on either side of the board.