Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems 7200.2 Recap

Hi,

I need some advice(reassurance). I have recapped my 7200.2 as the original Nichicons had lost some of their value, up to 50% in some cases.

I have used Panasonic FC throughout but now have an issue I am not sure on.

I powered up using a 150W DBT to make sure nothing goes wrong and all good.

When sat idle, theres no issue.

When I send a music signal, the speaker plays for 1-2 secs and then plays a strange bell type ringing noise. If I stop the music, the ringing continues for another second or so and then the speaker reboots itself.

I am now stuck, after many hours of research, ChatGPT has suggested that the low ESR of the FC could be causing an oscillation somewhere, however, I cant see anyone having issues with low ESR recapping with some using FR and FM caps I believe.

I am leaning towards the DBT starving the system and crashing the DSP board which is creating the odd sound. I am reluctant to go full mains, however, in case there is an actual oscillation.

I have double/triple checked all caps, orientation and soldering etc.

1)Do I just man up and go for it?
2)Has anyone recapped their DSPs with low ESR and no issues?
3)Has anyone powered with DBT and had the same issue?

Thanks all!

Steve

Hi Steve,

Whilst the speaker is still connected to the DBT, check for any DC offset on each amplifier output - they should all be very low (< 20 mV). If any are higher, then you need to investigate the associated amplifier section.

If that's OK, I would go for it and plug the board into the mains.

The DBT is likely restricting current to the amplifier, causing voltages to drop and the digital section to become unhappy.

I'm assuming you've re-capped both the comms and amplifier boards?

If you've not re-capped the other speaker, and you're still having issues on full mains voltages, then you could substitute the comms / amplifier boards from the other speaker to see where the issue is and then potentially work backwards (assuming you've not thrown the old capacitors away...)

Drop me a PM if you're still having issues.

Good luck,

Steve

Steve's Advice is always good, check that stuff first. Wish I had schematics but pretty sure they use the Cap ESR to help with the feedback loops for the regulators~ this will be 100uf/47uf caps (most likely). I used all Audio grade caps unless it was a filter cap (I'll copy them), as that's what Meridian did. If I was going to play around, would be Copying some of the SE amp board upgrades/bulk caps/resistors/bridge rectifier.

Hi,

Thanks for the replies, I binned all the old caps so no good. I have got some new nichicon UKAs to go in but would rather not recap the whole thing again. I have recapped both comms and amplifier boards. If it is instability, my research suggests it could be the lm317s oscillating due to the low esr, however, from what I have found is that noone has reported a similar issue.

Does anyone have a DSP7200 or similar they could run briefly on a DBT to see if it behaves the same way?

Hi,

I was waiting to see how long it would be before Steve offered a solution and as usual he is 'right on the money' ... and pretty damn quick too!!

As the goal of any Capacitor manufacturer would be to produce the lowest ESR components (a perfect capacitor) I am sceptical of the A.I. generated response ... as I am of anything generated by A.I.!!!

The LM317 appears a lot in Meridian Electronics and you only have to look at the number of large and small decoupling capacitors that generally follow them to question this.

Is it correct that both units are now performing in exactly this same manner or can you follow Steve's substitution suggestion, which is probably time consuming but undoubtedly your best bet?

I do hope you manage to locate the problem and I will be very interested to learn of the outcome.

Regards
Paul

Replace the LM317. They do go bad and don't hold voltage.
Buy a higher spec model.

Update:

Removed DBT and all working fine now thank god.

Thanks for your input

Hello Steve,

sorry for the question, but what is DBT ?

Robert

dim bulb tester. put a incandescent bulb in series with the mains input to put a lower voltage on the power supply’s input. If it glows brightly, there’s probably a short in the psu.