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  #166  
Old 12-09-17, 12:15 PM
martin clark martin clark is offline
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Something really, really not right with the 7220/psu; there's no way noth reg and chip should run that hot, when they didn't before. (SAA7220 runs warm, but comfortably so IME; 35-40degC tops) Oscillation, or you've killed something inadvertently I fear.

With the 7220 not powered up, yes the flea has to deliver a handful of mA - the SAA7220 logic inputs when unpowered 'look like' a diode or two, to 0v; so the clock signal in that state isn't necessarily awry

(the dac is quite robust IME, since so much of it is current logic - ie mostly 'looks like' a current sink/source on the supply pins and doesn't much care about absolute DC voltage, subject to working at all. I've one which withstood +12v on the +5v pin for some weeks...no damage, measured the same as ever! Philips often ran them on +6v in their own players etc)
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  #167  
Old 12-09-17, 02:14 PM
sq225917 sq225917 is offline
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Drop that 100n to 15n and you'll be closer to ideal for c-rc
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  #168  
Old 12-09-17, 11:03 PM
Dowser Dowser is offline
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Quote:
Originally Posted by martin clark View Post
Something really, really not right with the 7220/psu; there's no way noth reg and chip should run that hot, when they didn't before. (SAA7220 runs warm, but comfortably so IME; 35-40degC tops) Oscillation, or you've killed something inadvertently I fear.

With the 7220 not powered up, yes the flea has to deliver a handful of mA - the SAA7220 logic inputs when unpowered 'look like' a diode or two, to 0v; so the clock signal in that state isn't necessarily awry

(the dac is quite robust IME, since so much of it is current logic - ie mostly 'looks like' a current sink/source on the supply pins and doesn't much care about absolute DC voltage, subject to working at all. I've one which withstood +12v on the +5v pin for some weeks...no damage, measured the same as ever! Philips often ran them on +6v in their own players etc)
Thanks - I do not see oscillation (but then also have never seen oscillation...so do not know what it looks like ). I reconnect the stock 7220 power rail as next step.

Quote:
Originally Posted by sq225917 View Post
Drop that 100n to 15n and you'll be closer to ideal for c-rc
I thought Mark used 100nf and 10nF in his CheapoModo - and I just happen to have a whole bunch of them already. The kit arrived yesterday from US, so need to check. But all that can come once I get the damn player working again

Richard
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  #169  
Old 13-09-17, 08:09 AM
Dowser Dowser is offline
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Damn - 7220 and reg gets too hot reverting back to stock supply too I assume I must have damaged something when the 100uF cap exploded.

Looking at the cct (from a Marantz CD60), there is not really much external to the saa7220 itself that could be causing it, but I will have a quick check later this evening.

On the bright side, better a faulty 7220 than 1541!

Richard
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  #170  
Old 13-09-17, 10:26 AM
Dowser Dowser is offline
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Faulty SAA7220, normal temp now and audio again after replacement - question is, because of blown cap, or my DIY supply?

I check supply again and try reconnecting it later. I at least confirmed that the SAA7220 I replaced in Graham's CDI #2 wasn't faulty - not by fitting to CDI #1 I hasten to add, I took one from a working CD50 I have, then fitted Graham's into that (single sided PCB ).

Richard
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  #171  
Old 13-09-17, 11:54 AM
Dowser Dowser is offline
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Hmmm - need help. This is the stock supply (shared rail between 2 LM317 delivering a dedicated 5v for SAA7220, and then another for other digital chips;

Voltage at input to LM317;


Scope for noise (100mV AC);


I then took the DIY supply I built, put a 47 ohm 5W resistor between it and ground (just under 400mA load) - DC was just over 14.5v, scope trace;


Is that oscillation?

I then changed the CRCRC on the raw DIY supply - replaced the 1 ohm resistors with wire links. With same load I then get 16v DC and this;


A bit confused now - I did something very similar in my Marantz CD60 without issue - the only difference was that I only used one transformer winding and a bridge rectifier, whereas in CDI #1 I have used centre tap and full wave, so I'm effectively connecting CDI ground plane to the centre tap of the transformer. Is that causing an issue?

Thanks, Richard
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  #172  
Old 14-09-17, 10:21 AM
Dowser Dowser is offline
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C*nty-F*ck-Buckets! With the testing I did above last night I killed another SAA7220! Trying it tonight and no audio out, plays fine - chip was not overheating this time - check output from 7220 to 1541 and it's all messed up (comparing with CDI #2 on same shelf). Input to 7220 from 7310 was at least similar to #2, but still a collapsed clock signal.

So, out came Graham's original 7220 from the CD50 I fitted it to last night, and it is now in CDI #1 and all is well in the world.

I have now completely disconnected the new transformer's dual 12v secondaries from the rest of the player while I ponder...and seek advice

All I had was the centre tap of the transformer connected to the central Naim earth point last night, and then connected the 14v from the new supply, via a 47 ohm resistor, to the central earth point to measure things.

Even when I wrote it last night, I had a nasty feeling that directly connecting a centre tap winding to the main earth point was probably not a good idea, and I assume this is what has caused the issue.

While I have done it before when powering a Flea, the Flea PSU earth return is separate from the main Naim CDPs earth return. And when I made a dedicated MTPR 5v supply for the SAA7220 in my CD60, it was only using one secondary winding and a full bridge - so there were diode junctions separating the transformer for the CDPs main earth point.

I'd really like to know the technical reason behind it though - can anyone confirm?

I've ordered 4 new 7220s from a hopefully reputable source in China ($5 each with postage against Little Diodes 28 each plus postage...I can source a brand new 1541A for that here in CH!) - via AliExpress, so can easily claim money back if fake...but up to a 4 week wait.

Currently listening to CDI #1 with just the dedicated supply for Graham's modified Flea as the only mod (well, except for wet-tants in output blocking duties), and I am asking myself why I bother with further mods - it sounds fantastic

Richard
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  #173  
Old 14-09-17, 11:29 AM
Dowser Dowser is offline
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Wow - #1 now sounds better than #2 - why? Dual versus single crown, modified Flea, or center tapped Flea supply in #1 (vs bridge in #2) - no idea, intend to find out though

Interestingly, earlier even after replacing DRAM and SAA7310 in #1, it's lm317 was still running as hot as the dedicated one for the 7220. I replaced the 3 old blue tants around this 317 while doing recent work and temp is now back down lower that the 7220 one.

In Graham's I now notice both reg and 7220 are running hotter that those in #1 - tant replacements coming up all over too I think!
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  #174  
Old 15-09-17, 11:45 AM
Dowser Dowser is offline
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Hmm - I left it powered overnight, and the Flea has failed. Seems to be base-collector open circuit on the input filter bc550c fitted (rather than stock bc447c). Will a ztx751 do as a replacement pnp transistor?

Thanks
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  #175  
Old 15-09-17, 12:35 PM
martin clark martin clark is offline
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Any NPN will do, especially with the lowered input R in the filter BC547 or sim, any generic equivalent you have.
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  #176  
Old 15-09-17, 12:37 PM
martin clark martin clark is offline
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OK, this and the failures of SAA7220s - is your add-on transformers actually ok, or is it a bit 'leaky' from AC mains - say large inter-winding capacitances..? Is all well on the secondary side.. measuring output rails, prior to their interconnection with the player's 0v system..? beware of sending rectification currents through nominally 'quiet' 0v side planes/connections.

(I've a Flea powered-up for most of a solid 11yrs now, the CD2 player it feeds likewise, and no such failure!)
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  #177  
Old 16-09-17, 02:55 AM
Dowser Dowser is offline
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Yes, agreed, something not right.

I ran similar mods in a Marantz CD60 for 12 months or so no problem - key difference being I only used a single secondary winding and a bridge rectifier for each supply rather than centre tapped and full wave.

The Flea I originally fitted my my CDI back in 2015 was using center tapped and full wave though - and in that player the SAA7310 & DRAM failed 6 or 8 weeks later. However, I lifted the whole transformer/PSU/Flea out of the CDI and fitted it to a Woodside WS3 where it has ran successfully since March until I removed it from service a few weeks back.

Weird. I do some careful measurements again before connecting all back up.

Richard
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  #178  
Old 16-09-17, 02:51 PM
trancera trancera is offline
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Gosh I ain't logged in for eons, but reading this just thought I'd make a daft comment.

I have a flea in my Arcam 5 from the original gb kits (thanks Martin)

Anyway, a while after installing and enjoying some weeks I noticed something odd. When the Arcam was switched off the transport spins to I think full speed and sits like that.

Yes, I had tapped into the mains before switch for the little xfr by accident, idiot, but never did get round to working out why it was somehow powering the motor!

(likewise I was concerned re center taps etc)

Anyway you never know might be daft comment that generates a good idea.
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