| ash_dac |
Hi,
I built a separate supply for the saa7220 but stupidly didn't heatsink the 5V regulator. The regulator got very hot, and failed I guess!
I put the Saa7220 power supply back to how it was originally but now the thing does the spinning like it's going to fly thing.
Now I have a fantastic spinning machine.
I know where the problem is:-
-the clock was damaged
and/or
-the saa7220 has died.
I thought i'd measure with a multi-meter the voltage at the saa7220 vdd pin to ground to check the voltage.
As soon as I touched the ground pin with one probe of the multimeter I could see a spark ! (between the ground, and one multimeter probe). I tested during the hyper spin up.
Is this just the current that the saa7220 dumps onto the ground rail!!!! :hot: |
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| hembrow |
The SAA7220 doesn't draw so much current that it would instantly incinerate a 5 volt regulator such as a 7805. My 7805 only has a very small heatsink on it and runs at a very reasonable temperature.
So, I think you've done something else wrong. Did you test for shorts before switching on ?
What input voltage do you have to the regulator ? They usually need to drop about 3 V or so (i.e. 8 V input). Any extra above that simply produces extra heat and at some point you exceed the voltage that the regulator can cope with.
Did you test that the regulator output really was 5 V before connecting it up ?
David. |
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| ash_dac |
| quote: | Originally posted by hembrow
The SAA7220 doesn't draw so much current that it would instantly incinerate a 5 volt regulator such as a 7805. My 7805 only has a very small heatsink on it and runs at a very reasonable temperature.
So, I think you've done something else wrong. Did you test for shorts before switching on ?
What input voltage do you have to the regulator ? They usually need to drop about 3 V or so (i.e. 8 V input). Any extra above that simply produces extra heat and at some point you exceed the voltage that the regulator can cope with.
Did you test that the regulator output really was 5 V before connecting it up ?
David. |
shorts: possibly on the regulator
I measured 12V input into the regulator. Quite alot to drop so heat!
Upon testing the 5V regulator this evening it wasn't working.
Well the player started playing music, and then stopped!
I have tested the clock today, and it doesn't work. |
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| jean-paul |
That SAA7220 is dead. Do you have a spare one ?
Please measure the new supply with SAA7220-like load before going on with any further changes. |
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| ash_dac |
| quote: | Originally posted by jean-paul
That SAA7220 is dead. Do you have a spare one ?
Please measure the new supply before going on with any further changes. |
I have a spare one but it's soldered to a board.
I will have a look tonight. |
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| hembrow |
| quote: | Originally posted by ash_dac
shorts: possibly on the regulator
I measured 12V input into the regulator. Quite alot to drop so heat!
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What is the regulator ? 12V is OK for a 7805 input so long as you're not drawing loads of current and so long as you have enough heatsink.
| quote: |
Upon testing the 5V regulator this evening it wasn't working.
Well the player started playing music, and then stopped!
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This is confusing. If the player ever manages to make music then the SAA7220 is still working. When you say the regulator wasn't working, do you actually mean that it worked for a bit until it overheated ?
| quote: |
I have tested the clock today, and it doesn't work. |
But you said music came out of the player. That's not going to happen if the clock isn't working.
From reading between the lines of what you said, it appears that:
When you tried it before, the player worked for a bit and then stopped. You noticed at that time that the regulator was very hot.
Today it worked for a bit again and then stopped.
To me, this suggests that everything is fine except that your regulator is overheating and shutting down.
As the player needs a working SAA7220 and clock to make any sounds at all, this must still be working when it's got a good power supply. However, after the power supply goes out when you overheat the regulator, you're not going to be able to see anything much around the SAA7220 - including the clock. So, if I were you, I wouldn't bother butchering the board to replace the chip until I'd got a stable power supply.
Have you tried simply bolting a lump of aluminium to the regulator ? If your regulator is a TO220 package 7805, the heatsink will be connected to the centre pin which is 0V, so make sure it doesn't short against anything else.
If your regulator is not a 7805, what is it ? A 78L05 (tiny package without heatsink) is probably not up to the job.
So far as heatsink size is concerned, you shouldn't need much and that makes me wonder if your 5V rail is being pulled down by something else. Back in 1989 I installed a 7805 with about 5 cm^2 of aluminium attached as a heatsink in my CD player to supply the SAA7220. This worked just fine up until last year when other parts of that player finally gave up the ghost. My current CD player has a similar arrangement. |
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| ash_dac |
Hi,
I have just soldered the crystal back into the player instead of my clock, and took out the regulator (thanks for tips).
The player now reads a disc, and sound is ok.
My thoughts were that it was a clock problem probably a dry soldering joint or failed regulator on my clock module causing the player to go warp speed!
I still don't understand why there was a spark!
Does the warp speed cause the saa7220 to spark ?
Any ideas ? |
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| hembrow |
| quote: | Originally posted by ash_dac
Hi,
I have just soldered the crystal back into the player instead of my clock, and took out the regulator (thanks for tips).
The player now reads a disc, and sound is ok.
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Good. No harm done, then.
| quote: |
My thoughts were that it was a clock problem probably a dry soldering joint or failed regulator on my clock module causing the player to go warp speed!
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When I had a player spin like that it was due to IDC cable connectors having become less conductive than they ought to be. I doubt it's actually anything to do with the SAA7220 itself as that's just the oversampling filter. Some people take that chip out altogether and still have a working player. So, you'd upset something else, quite possibly due to the clock not working.
| quote: |
I still don't understand why there was a spark!
Does the warp speed cause the saa7220 to spark ?
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No chip would store enough energy to create a spark. For that you need a capacitor. Almost certainly you shorted out a largish power supply capacitor. Quite possibly your probe shorted the 5V to 0V, or something similar.
You have still not described just what you had connected to the player. It's not really possible to say much without that information. |
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| ash_dac |
| quote: | Originally posted by hembrow
Good. No harm done, then.
[B]
When I had a player spin like that it was due to IDC cable connectors having become less conductive than they ought to be. I doubt it's actually anything to do with the SAA7220 itself as that's just the oversampling filter. Some people take that chip out altogether and still have a working player. So, you'd upset something else, quite possibly due to the clock not working.
[B]
No chip would store enough energy to create a spark. For that you need a capacitor. Almost certainly you shorted out a largish power supply capacitor. Quite possibly your probe shorted the 5V to 0V, or something similar.
You have still not described just what you had connected to the player. It's not really possible to say much without that information. |
Hi,
It was a 5V regulator with a 11.2896Mhz canned oscillator on a DIL socket. I was going to upgrade the oscillator to a low jitter type. |
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| Guido Tent |
| quote: | Originally posted by ash_dac
Hi,
I still don't understand why there was a spark!
Any ideas ? |
very likely ESD, you and your multimeter where at different potential than the SAA
I always touch the cabinet first, with my hands or soldering tip or multimeter
best |
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| ash_dac |
| quote: | Originally posted by Guido Tent
very likely ESD, you and your multimeter where at different potential than the SAA
I always touch the cabinet first, with my hands or soldering tip or multimeter
best |
Hi,
Thanks for the reply.
I normally touch the metal end on the radiator. |
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| Guido Tent |
| quote: | Originally posted by ash_dac
Hi,
Thanks for the reply.
I normally touch the metal end on the radiator. |
OK, any metal besides IC pins is better. You can still create sparks but the current distributes different, at least not through one pin or protection. |
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| hembrow |
| quote: | Originally posted by ash_dac
Hi,
Thanks for the reply.
I normally touch the metal end on the radiator. |
If by radiator you mean your central heating radiator, that's not really appropriate. It'll stop you having a huge potential relative to earth, but not necessarily relative to the CD player.
If you mean the heatsink radiator fins at the back of the CD player, that's better as it should leave you at the same potential as the player itself and you'll do no harm if you touch things inside.
| quote: |
It was a 5V regulator with a 11.2896Mhz canned oscillator on a DIL socket. I was going to upgrade the oscillator to a low jitter type.
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Yes, but this isn't enough information to help you.
I've asked some of these questions before... What type of 5V regulator and how was it connected ? What power supply went to the regulator input ? Did it come from inside the existing player circuitry or is it from an external transformer, rectifier and caps ? If a separate PSU, were the 0V lines connected together between this PSU and the player ? What evidence did you have that the oscillator was oscillating at all ?
You suggested before that you'd used a new regulator to supply the SAA7220. Is this the same regulator as provides power to the oscillator or a different one ?
Maybe it would help if you were to draw a diagram of exactly what you had connected to your player.
David. |
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| Fin |
| quote: | Originally posted by Guido Tent
OK, any metal besides IC pins is better. You can still create sparks but the current distributes different, at least not through one pin or protection. |
Is it relatively safe to touch the silicon part of an IC - without using ESD protection? |
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| ash_dac |
| quote: | Originally posted by hembrow
Yes, but this isn't enough information to help you.
I've asked some of these questions before... What type of 5V regulator and how was it connected ? What power supply went to the regulator input ? Did it come from inside the existing player circuitry or is it from an external transformer, rectifier and caps ? If a separate PSU, were the 0V lines connected together between this PSU and the player ? What evidence did you have that the oscillator was oscillating at all ?
You suggested before that you'd used a new regulator to supply the SAA7220. Is this the same regulator as provides power to the oscillator or a different one ?
Maybe it would help if you were to draw a diagram of exactly what you had connected to your player.
David. [/B] |
L7805 regulator.
Power tapped from existing raw power supply both ground, and vdd.
I had two L7805 regulators connected to the same rail (separate reg for oscillator, and saa7220). Note the two regulators were mounted on the same board, and were quite close to each other.
The oscillator was working before I added the extra saa7220 regulator.
I've put the player back to it's orignial state (orignal quartz clock, and resistor supplying saa7220).
As suggested i've drawn what I did, and I can see the grounds I made were wrong (atleast at saa7220 end).
How did you connect up a supply for the saa7220 ? |
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| hembrow |
| quote: | Originally posted by ash_dac
L7805 regulator.
Power tapped from existing raw power supply both ground, and vdd.
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OK. Those tend to be fairly sensible, and using the power already inside the player means you're not going to have a separate 0V to worry about. I take it for granted that "existing raw power" does mean DC after bridges and caps.| quote: |
I had two L7805 regulators connected to the same rail (separate reg for oscillator, and saa7220). Note the two regulators were mounted on the same board, and were quite close to each other.
The oscillator was working before I added the extra saa7220 regulator.
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This is a bit odd. 7805s should not have any effect on one another. Their proximity isn't important. Even if the heatsinks are connected together, both are at 0V. Are you absolutely certain that you didn't mis-connect something when you wired up the second regulator ? If you put them back to back, is it possible that you connected the input and output the wrong way around on one of them ?
I assume you had some capacitance on the inputs and outputs of the 7805s.
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I've put the player back to it's orignial state (orignal quartz clock, and resistor supplying saa7220).
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And you said it was working fine now it's back in one piece, which is great.
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As suggested i've drawn what I did, and I can see the grounds I made were wrong (atleast at saa7220 end).
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From what I can see in your diagram they are only "wrong" in the sense that the ground to the 7220 ends up meandering through the clock first. It may be better to have a star earth. However, this is a second order effect. I'd have expected everything to still work, but that you might not have had, say, the positive effect on jitter that you'd hoped for.
If the clock is currently in a working state on the separate board with the single 7805, then you ought to be able to wire that to the player without any other changes at the same time.
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How did you connect up a supply for the saa7220 ?
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I used DC from inside the player much as it sounds like you have. I took it from the same source as the existing 7805. My 7805 is mounted very close to the SAA7220 (within a couple of cm), with its own bypass caps right next to it. The thinking is that as the 7220 gives the power supply a bit of a hard time it wouldn't be helped by the regulator being distant and supplying current through long pieces of wire. It's all "star" earthed back to some convenient point on the PCB which is a good solid lump of copper close to the bridge rectifier and the rest of the PSU. Given that I was working around the mess of PCB tracks already inside the player it's not really possible to end up with true star earthing without removing an awful lot of PCB tracks and putting in a lot of replacement wires so this seemed as close as I could get.
I'd suggest that you put the 7805 for the SAA7220 right next to that chip as I did, and if that works you can then try adding the clock with its power supply as a second step.
I'd be interested to know where you got your relatively cheap oscillator from as I've been looking for one myself. I thought I'd found a nice cheap €3 oscillator from a Norwegian company but postage made it more like €50 ! |
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| ash_dac |
| quote: | Originally posted by hembrow
I'd suggest that you put the 7805 for the SAA7220 right next to that chip as I did, and if that works you can then try adding the clock with its power supply as a second step.
I'd be interested to know where you got your relatively cheap oscillator from as I've been looking for one myself. I thought I'd found a nice cheap €3 oscillator from a Norwegian company but postage made it more like €50 ! [/B] |
Hi,
Thanks for the response.
I mounted the oscillator on a 8-DIP so I could upgrade to the Tent clock.
http://www.rapidelectronics.co.uk/r...29223&XPAGENO=2
What other mod's did you do to your player ? |
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| hembrow |
Thanks for the URL.
I'd really appreciate an explanation from Guido Tent of how his oscillator differs from one of these. I am sure they do differ, but how ? What difference does this difference make to measured performance ?
After all, the metal cans around them both make them look pretty near identical and hide all the internal parts and design. The advantage of removing the clock from the (quite possibly not very nice) internal oscillator of the SAA7220 exists with either oscillator.
| quote: |
What other mod's did you do to your player ? |
Apart from around the SAA7220, I changed the op-amps (I put in OPA2604, which others seem to be removing...), bypassed power supplies to the DAC and the op-amps and removed the (nasty CMOS switch based) volume control circuit.
It seems to sound pretty decent. |
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| Guido Tent |
| quote: | Originally posted by hembrow
Thanks for the URL.
I'd really appreciate an explanation from Guido Tent of how his oscillator differs from one of these. I am sure they do differ, but how ? What difference does this difference make to measured performance ?
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is there a jitter spec given ? |
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| poynton |
| quote: | Originally posted by Guido Tent
is there a jitter spec given ? |
As Elso would no doubt say - Measure with your ears ;) :D |
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| hembrow |
| quote: | Originally posted by Guido Tent
is there a jitter spec given ? |
Hi Guido, I was hoping you'd reply.
No, there isn't a jitter spec given. Of course, that lack of information doesn't really tell us much.
I'm quite happy to believe that your oscillator is better in this regard, but for you to know that implies that you've a way of measuring the jitter from your own oscillator and comparing them.
So, have you measured any of the cheap ones to see how they do by comparison ? How does your circuitry vary from the cheap ones ?
I'm not in any way trying to catch you out - I'm simply curious to know what the difference is. |
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| riccardo |
| quote: | Originally posted by hembrow
Hi Guido, I was hoping you'd reply.
No, there isn't a jitter spec given. Of course, that lack of information doesn't really tell us much.
I'm quite happy to believe that your oscillator is better in this regard, but for you to know that implies that you've a way of measuring the jitter from your own oscillator and comparing them.
So, have you measured any of the cheap ones to see how they do by comparison ? How does your circuitry vary from the cheap ones ?
I'm not in any way trying to catch you out - I'm simply curious to know what the difference is. |
Just a question.
But if our cdplayers sound well (+/-) with old can oscillator, and, some clock like Elso KC7 sound very very good with the old can oscillator, could be possible that these new and cheap crystal are better than our old can quartz?
it is seriously believable that science changes to a shape getting worse the performances ? After 25 years? So it's old the can oscillator that sound in my old cdplayer......
ciao
RR |
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| ash_dac |
Guido,
The saa7220 provides the clock for the tda1541a processor by internally dividing the 11.2896 clock by 2. Is this correct ?
The saa7220 latches the WS, and Data outputs to the derived 5.6448 MHz clock output signal. Is this correct ?
If , as others have done on the forum, we clock the tda1541a directly must we also relatch the WS, and Data aswell?
BCK output of Saa7220:-
( 44100 X 16 X 2 X 4 = 5.6448 MHz ) |
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| Guido Tent |
| quote: | Originally posted by ash_dac
Guido,
The saa7220 provides the clock for the tda1541a processor by internally dividing the 11.2896 clock by 2. Is this correct ?
The saa7220 latches the WS, and Data outputs to the derived 5.6448 MHz clock output signal. Is this correct ?
If , as others have done on the forum, we clock the tda1541a directly must we also relatch the WS, and Data aswell?
BCK output of Saa7220:-
( 44100 X 16 X 2 X 4 = 5.6448 MHz ) |
Hi Ashley,
Correct, clock/2. Reclocking the other signals is worth the trouble, allthough the impact is smaller compared to directly clocking pins 2 & 4 of the TDA1541.
Give the extra reclockers their own power supply to avoid data related crosstalk to other circuits.......
best |
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| ash_dac |
| quote: | Originally posted by Guido Tent
Hi Ashley,
Correct, clock/2. Reclocking the other signals is worth the trouble, allthough the impact is smaller compared to directly clocking pins 2 & 4 of the TDA1541.
Give the extra reclockers their own power supply to avoid data related crosstalk to other circuits.......
best |
Thanks for the reply.
Is 5.6448MHz direct, and X 2 to saa7220 worth trying ?
Pll clock multiplier ? |
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| Guido Tent |
| quote: | Originally posted by ash_dac
Thanks for the reply.
Is 5.6448MHz direct, and X 2 to saa7220 worth trying ?
Pll clock multiplier ? |
Hi Ashley
I'd propose /2, instead of *2. Easier to make, unless you do a good PLL, but makes it more complex.
best |
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| ash_dac |
| quote: | Originally posted by Guido Tent
Hi Ashley,
Correct, clock/2. Reclocking the other signals is worth the trouble, allthough the impact is smaller compared to directly clocking pins 2 & 4 of the TDA1541.
Give the extra reclockers their own power supply to avoid data related crosstalk to other circuits.......
best |
Guido,
How should we treat WS ?
Have you ever put WS signal from Saa7220 on a scope ? |
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