saa7220 gets warm??

[jnewbold]

I have just added an LM317 +5V regulator to the SAA7220 filter chip in my Rotel RCD965BX. The regulator is fed by one of the secondaries of a transformer PSU. The other secondary tfeeds four similar LM317 regulators for the 5V digital supply pins on the SAA7323 DAC. Another separate transformer PSU feeds the DAC analog 5V regulators. These have been function for a couple of weeks.

Now, I notice that the SAA7220 chips gets quite warm. Not too hot or even uncomfortable to touch but quite warm. The 317 reg is fitted with a TO220 type heatsink which also gets warm.

I don't know whether to be concerned about this or not, because I don't know whether the chip was getting warm before the new regulator was installed and I know that the SAA7220 draws typically 180mA, so it is likely to get warm.

The regulator output voltage is 5.12V and it's bypassed with a 100uF/10V Rubycon ZL cap at the output. The regulator is located within about 3cms from the supply pin with the ZL cap halfway between the pin and the reg. The cap was chosen for a not too low impedance (0.30R). This is the same configuration which has been working well on the DAC digital and analog 5V regulators.

The other issue that I have encountered since putting the new reg on the 7220 is that the disc drive will not read discs. It performs all its functions – except reading. The disc spins and the laser tries to focus, but no disc information is displayed. When I press "play", the disc spins for a moment and then stops. I can see that the laser is working.

Any ideas.

Joe

[musicomputer]

SAA7220's do get warm so don't worry about it.

Regarding your problem, check that the flex circuit from the cd mechanism is correctly seated in its socket and the locking clasp is pushed down.

cheers

[jnewbold]

SAA7220's do get warm so don't worry about it.

Thanks, I was hoping someone would say that. I just han't noticed it before.

Regarding your problem, check that the flex circuit from the cd mechanism is correctly seated in its socket and the locking clasp is pushed down.

Yes, I have checked that ribbon flex and cleaned it with Caig Deoxit. I have reseated the flex a couple of times - and nothing changed. maybe one more time ...

Joe

[jnewbold]

I have cleaned and reseated ribbon flex of the 4/19 mechanism, after inspecting it with a magnifying glass to see if there are any cracks in the traces. I couldn't see anything amiss. However, the problem is still there.

When the drawer is closed and empty, the display shows a line of dashes with no other symbols. However, when a disc is inserted in the drive and the usual focusing and reading takes place, the line of dashes is joined by a disc symbol, as if the drive has recognized that there is a disc , but does not read it.

The laser is on, the head moves up and down and the radial arm moves as they usually do when focusing focusing.

I can measure up to 45mV, briefly, When I press the play button, the disc spins up for a moment and the laser head searches, but then it stops. During this manoeuvre I can measure up to 45mV, briefly, across the laser test point. The service manual recommends 50mV +- 2mV at this point.

Any other other suggestions?

Joe

[PetrL]

Is the SAA7210/7310 in this Rotel? If yes, you din't change the electrolytic cap on pin 22 for a bigger one in the hope for the best, did you? It can worsen/damage readability. (my saa7220 gets warm too)

[jnewbold]

Hi PetrL,

Thanks for your reply. Do you have a Rotel RCD965 or another player with the same chip set?

Is the SAA7210/7310 in this Rotel?

The Rotel has SAA7310 in 44 lead QFP package (surface mount).

you din't change the electrolytic cap on pin 22 for a bigger one in the hope for the best, did you? It can worsen/damage readability.

Pin 22 on my version of the 7310 is one of the output signals to the external RAM and has no capacitor on it. However, the data sheet shows that the 40 pin DIL version has a cap on pin 22 (PD/OC). Is this the cap you mean? The data sheet also shows that the equivalent pin on the QFP (SMD) version is pin 29. On the Rotel schematic, pin 29 has a 75R resistor and a 2.2uF 25V cap to ground.

I have just gone and looked at the PCB and realised that I have mistakenly replaced that 2.2uF cap with a 47uF Rubycon ZL. This cap is very close to the bypass caps for the 7220, 7310 and DRAM chips and I must have changed it when I changed the bypass caps to those chips.

I will change the cap back to 2.2uF tomorrow. Should I use a general purpose type capacitor?

How does the value of this cap have such an effect on the readability?

Many thanks for your reply. I would not have noticed my mistake without your question.

Joe

[guido]

Originally posted by musicomputer
SAA7220's do get warm so don't worry about it.
cheers

Once fixed my cd80 and had all out of the case on the floor. Pcb was up side down so i could measure on the bottom. The 7220 died.... Reason unknown. Maybe i made a mistake during measuring, maybe too hot.

Luckily spare parts are no problem, any el cheapo philips player from the right era will do

[PetrL]

I will change the cap back to 2.2uF tomorrow. Should I use a general purpose type capacitor?

I bet your player will work again after that!

I'm not sure how to determine this combination of R and C, anyway in each player with this decoder the combination is slightly different. I think Philips or Rotel for that matter have chosen always the best compromise for a given model (maybe the key to good trackability of all Philips machines?) Once I experimented with this, it is possible to increase space or ambience in the sound, but at the cost of higher noise I'm affraid. The player however started to have problems with read-in of some CDs, so I returned to original 20 years old cap (could not get 6.8uF locally and was disappointed by experimenting further in this arrea).

[jnewbold]

I have put in a new 2.2uF cap but the player is not back together yet. I will probably be able to do it tonight (it's 5.37 pm here). I could not put back the old cap because I had destroyed it when taking it out.

I will post the result when it is all back togther.

Joe

[jnewbold]

Hi musicomputer, PetrL and Guido,

The player is now working properly. Restoring the capacitor to 2.2uF fixed it. :

The bonus is that the SAA7220 is obviously working. Before I put the player together again I reconfigured the regulator with a larger heatsink and located it in a more open space, but still close to the chip. I also stuck a small heatsink on the 7220. Its still warm but I have ceased to warry about it.

I have been trying to understand why that little capacitor on pin 29(22) of the SAA7310 has a big effect on the disc reading capability of the player. The data sheet says that pin 29(22) is the PD/OC - Phase Detector output / Oscillator Control where "The outputs of the frequency detector and phase detector are summed internally, then filtered at this pin to provide the frequency control signal for the VCO."

The pin has a resistor and cap in series to ground so the filtering must be on the low side. Am I correct in thinking that substituting a significantly larger capacitor changes the frequency control signal and prevents the disc being read? I know that any issue with the main system clock can cause the disc to spin counterclock wise or very fast so I assume that any change in frequency will have an adverse effect on disc reading.

Thanks for your help and comments.

Now for a discrete out-put stage to replace the opamp – and low noise regulators

Cheers,

Joe