MHZS - Mystery of the DAC Chip

Hi Friends od Modification,

working on a MHZS CD66 now I find out the mystery of the chip and another really interesting secret about the circuit. I think the CD33 has the same circuit problem.

Please take a look.


It is not a proprietary development, how it is to read in advertisement. It is a BurrBrown PCM 1742KE from Texas Instruments.


After this I studied the signal path in my CD66.

1. Look at: focus.ti.com/lit/ds/symlink/pcm1742.pdf (Page 6).
The analog output is on pin 7 and 8.

2. The signal goes through the cheap and low quality electrolytic Caps on the right side over the DAC. Imprinted is 100uF/16V. In fact, there are two 100uF/25V.

3. The next is the OPA.

4. Following are the two 0.47 uF Multicaps.

5. The 12AX7.

6. Two really cheap electrolytics again.

7. The Relais


Friends, take care by working o the PCBs. The Multicap 1uF has a voltage of 38 V after taking out the PCB (and after more than 3 hours).

The same is on the other PCB. The Voltage at the Pins ( printed is 100V and Ground) is about 52 V after some hours!

So, can somebody tell me why I cannot find the MHZS homepage?

And which tubes are now really good?

Grettings from Germany

Some of you have changes the two multicaps. Think about it that the signal flow is about Caps No 2 and No 6.  Better to change them first.

....... does anybody know whitch value will be correct to change? Caps No 2 are 100uF, caps No 6 are only 10uF and the Multicaps are 0.47 uF. I think they should be all the same value but I'm not really sure.

Hi,

thats correct.

I didn`t know how the cover of MHZS has been fixed. So at first I have desoldered all solder joints under the cover and then pulled up carefully the cover. Use than a hot-air gun, but don`t blow too long on this epoxy, you will damage the parts around the epoxy. So: max. 20 seconds with 450 degree Centigrade and then carry up 2 Milimeters of this white mass.  Thats to repeat several times. You will need with the hot-air gun 2o - 3o minutes until it lookes like at my pix.

And the second: After turning off the machine some caps stay charged and don't discharge itself. I am going to shot some pix and post them in some minutes.

Now some tips for your health!

I measured high ( dangerous high ) voltage on cap No 1-please look at my photo. Also there is a high voltage on the connector No. 2. This connector is connected on the left side to No. 3 in my photo.

I took a resistor ( 150 kOhms and 2 Watts ) parallel to cap No.1 and soldered him under the PCB.

Next I do the same under the pins of No. 3, because its easier as to solder under the connector No.2. So you dont worry about the voltage coming out of connector No. 2.

Problem is that the wiring of the 2 Watt resistors is to think and goes not through the PCB. At No. 3 there have to be some small caps to clean the high frequencies, but MHZS or who else has economized this caps ( and the other 50 haw you see on your own board). You can use that solder joints to bring your resistor there.

The result is good. After turning off my voltage falls down to 1 Volt in some minutes.  

Hi Blair,

you wrote your CDP has this intermittent static sound in the left channel. Not easy to say something about it. Can you change the tubes again and write what has happened?

Sometimes I mod and mod and mod and after starting I must see the machine works not correctly. The best what I can do - if you believe it or not - is to go sleep and don't touch the machine again. ( You must know I mostly mod at late evening and night ).

Next day you think clearer about your work and then pull out the PCB and check all solder joints with a multimeter in all ways. Set up your multimeter on "Ohm", for messuring resistors. Often it has happened this: A line on PCB goes from point A to B to C to D. My soldering joints look very good, but the multimeter says A to B is OK, C to D is OK, too. The solder joints from B and C are only connected to their neighbour A und D, but not together! So a pod or a way on PCB at point B or D is broken. You will see it because the multimeter says Ohms=infinite.

Then I heat the solder again very carefully and meassure again. If the multimeter says again "infinite", you take a small wire and solder this points manually together. That looks not good but it helps.

After many mods in the last years I find out that there is another way to best caps without damaging the PCB. Look at my next pix. Now I am testing much caps and different combinations on the Headphone Amp Xiang Sheng 708b.

I soldered some hard wire without isolation an that pionts where I am not sure which value is the best and let the cabinet open. Then its easy and goes fast to change values and qualities of caps. Every day another value! :wink:

After two weeks I find out what sounds best and pull out the hard wires and everything what I have burned with the soldering iron. Then I calculate my budget and order the really good caps which should stay in.

Thats the way to find out what applies to your music style and your habits. And its economic. I am sure you have enough unused caps there! :wink:

And your result will be very very good, you will see.

Some posts before I wrote about bypassing ecaps by a resistor. Here are some pics for the same solution on the headphone amp. The only difference is that in CDP I soldered both sides together and in the amp not, because this big blue caps are not part of PSU, they are part of coupling between main PCB and headphone jack. So there is to cut one side after soldering.

When I put out the amp and want to work on it I push the contacts of the resistor and the cap together, but only with an isolated screwdriver!!! The discharging takes two minutes, the voltage falls from 80 V to 2 or 3 V. After last mod I will take this resistors out, of course.  

You go the same way in your CDP, I would recommend it.

Now to the MHZS Mystery Chip 8)

In the description of the manufacturer TI the BB PCM1742KE needs two supplies: 3.3 V for Digital and 5 V for Analog Part. A possibility is to take the 3.3 V from the main 5 V supply.   I studied the PCB very carefully and find out thats the way MHZS has gone. BUT: TI recommends in his datasheet ( look here: http://focus.ti.com/lit/ds/symlink/pcm1742.pdf ) to give two separate voltages from two different PSUs to the chip. They write that would be very important to get a good sound quality later. I think I will do that and post the results.

On the other side you will see on your PCB that the cheap ecaps ( in post before ) sit between pin 7 and 8 ( analog signal ) and the OPA.

Now............ the missing small blue caps for high frequency eliminating (about 50!), the missing double PSU, the low quality electrolytics ( 4! ) and and and.........there is much air for new ideas

Now its time to look for new PSU caps. Havent forget them, but only the most important first

Hi Blair,

you picture gallery looks very nice!!    I haven`t webspace so I will post some pics here, two of my projects have been really hard but very good. But one thing is not to forget: My experience is that a good clock can make a CDP coming up from a minicar to a rocket!

Changing caps is sure necessary but changing clock is the best I ever have done. On the next pics you will see it on the example TEAC VRDS-20, my last project........4 month work................ :wink:

Hi Blair,

I  hope you have managed to solder the new DAC. How are the results?

If you have trouble with your pickup try it here, they have everything:

http://www.ersatzteil.justone-schnepel.de/index.html


Now to the pics......at first from the CDP which I used as transport.......

the Audiomeca Elixir DAC, a fine thing from Pierre Lurne. Good to see that there are not so much devices on the PCB as somebody would say, and the DAC is a Phillips, the DigFilter is a Crystal and the OP Amp from AnalogDevices. Interesting how few devices but such unbelievebable good sound.

The Denon DVD Player DVD 2800 Mk II

The second pic is the origin condition....you buy here a lot of free space for more than 1600 USD...... please ignore the advertising of silicon image......this pic is the only one I have found on the net.

oh....I am sorry, this is now the second pic from below .... the forum is sorting pics the other way around......


now the rest.........I think the Vincent ( is the German name, in other countries called SHENG YA ) is to colorless inside........here an original pic ( somewhere between the others, with the white beams ).....

The loudspeakers have been a DIY project from the german magazine Stereoplay.  :arrow:  http://www.stereoplay.de/stp/home

The order is again not correct.....Sorry :roll:  

I brought in some Mundorf caps and coils. As wiring I used Linn K20. Its OK for that price, because there are about 20 meters used for the speakers.

If you have questions feel free and ask

Hi Blair,

thank you very much.  

Now I am looking at the little DAC. A real advice I dont have.  :?  So I take a look on the datasheet. Thats what I have found:

Storage temperature, Tstg –55°C to 150°C
Junction temperature, TJ 150°C
Lead temperature (soldering) 260°C, 5 s
Package temperature (IR reflow, peak) 235°C

So I wish you a quiet hand and luck, dont solder him too hot or too long. And please dont take too much solder, it will be difficult to remove it later if the circuit points glue together.

Later I will handle the lens. The task is to minimize the diffused light of the laser. Its the same procedure as on the TEAC and DENON. You have seen it on the pics? The border of the lens is to colour with black resistant paint. Thats usually the first I do by modding. I will make pics and post them with description. Do you want to do that too? Its independent from your DAC soldering, easy and has a real effect, not vodoo .  

Good luck,

Kiko

Hi Blair,

yes it is easy but please dont start it, I have some tips for you.

You need cotton swabs or Q-tips ( whats right now :? ) and pure alcohol. And an usually permanent marker.  This work daubts a little bit, so I can show you how it goes easily and fast. :wink:

Blair, dont give up. If you damage the chip, order a new one and go with him to a specialist. Can you tell me how much you payed for this chip? The only problem you can have is that you damage this fine wirings on your PCB. Then nobody could solder in a new chip.

As I have damaged my first PCB ( with the open cover ) a Hongkong dealer told me, both new full assembled PCBs for CD66 and airmail shipping to Europe will be 190 GBP plus customs tax. For your CD33 it would be nearly the same price.

So be carefull will it.  :wink:

OOOOOOPS, have forgotten somehing:

you must totally discharge yourself, the board and the soldering iron! This chip has a electrostatic sensivity.

So put in one resistor as I told before, meassure all pionts where are ecaps are, everything must be at 0 V. If you use a soldering iron with a transformer station you must discharge him with touching the top shortly with your shockproof socket ( on earth!!). And.....hmmmm......I discharge myself when I sit there ( after going about a carpet where your body charges everytime ) by touching the earth phase of my shockproof socket . But be carefull you can touch the hot wire. I hope you dont make this mistake! Or buy a bracelet for technicions, that a wire to the shockproof socket and you are so connected on earth the whole time you have it on. :wink:

HI Blair,

can you make a pic of that and post? If there is some epoxy an the leads, can you use a hot air gun and a screwdriver? The epoxy will be squashier then.

Kiko

Blair,

looks very good what you have found there! And interesting how persistent you are!  8)

Do how have changed the both tubes before pulling up the dac?

Blair,

my position is the same, I like that too. But what I dont understand is why you will never mod again. Is it because your CDP makes this problems? After watching your pics I believe you are in your heart a DIYer and when you buy the next one, or an amp or anything else you will do it again.  :wink:

So I hope it is the DAC what makes this malfunction. What will you do if you change this chip and the intermittant static sound comes again? Where do you bought this CDP? Do they sell spareparts?

Kiko

So, now the work on the lens. I recommend to do that on all players, how you have seen above its a good thing for DVD Pl. too.

You need a permanent marker, some Q-tips and little bit of spirit ( ethyl alcohol ) and 10 minutes time.

You can pull up the cover so you can better paint 360 degree. Now hold that slide with 2 fingers. The slide is undetermined. Be careful not to break the slide. The mounting suspension is very softly. Paint the lens 3 or 4 times completely around, not only the border, but also not in the middle.

If you want to be sure that your painting is 360 degree around you dont need a strong illumination. You have a blue LED there. :

Make the Q-tip wet with ethyl alcohol, dry him a little bit and touch the lens from above, fix the Q-tip with two fingers and turn him on the upper side. Very easy......

Now polish the lens with the other side of the Q-tip. Play a CD. Print forward/backward on your player. Look a the rotation of the CD. Is everything OK you can put the cover back. Something not ok? Does the rotation behave strange? Than take a new Q-tip and make the clear flat of the lens a little bigger. The same procedure.

Dont worry if the CDP wants not to play, that is only a sign that the clear-transparent flat is too small. The CDP is not defective! That has happened here today, too. No problem.

So....the cover and the LED are to screw back. Thats all. Costs = 0. The result: More stability and the music is more flowing.

Try it and you will hear the difference  8)

Hey Blair,

I like your idea. 8)  Very fine!

Sometimes I play with the same mind. Is there a homepage I can visit?

...deleted message

Yes I have got it. Thank you.

hey,

does anybody know good values for caupling caps for mhzs players?

thanks, kiko

Hi Alfcat,

marking the edge of a CD to reduce the reflection by the lens is correct, but the reflection happens on the edge of the CD and on the edge of the lens. Think about your camera, the objective is nontransparent, only the lens is transparent. I heard the lenses of laser pickups had to be build in the same way but the industry searches the cheapest way. The different colors have a reason. The pickup works with 650 nm laser. This is in infrared area.

So the modders try to find a way to absorb the light on the edge and because we cannot see infrared light everybody searches his own way of the best absorption. So some modders believe in purple, some in green. The modding scene has true differences here in Germany.

I have often heard of green as the right colour. You have seen I used black. Thats why I believe that black absorbs best. But if its true I cannot say. I tried that different time and had with black color the best performance. Of course if you believe something else would be better, try it.

Will you please post what you are doing? Will be interesting!

I will post the pics, hope they are better as the last one. They are the best my camera is able. On the last pic the lens seems to be complete black. It is of course not, it is a mistake of my cam!!

Greetings!

Hi Alfcat,

I know the black CDs. But I know them only for Playstation Games. The PS 2 uses them. Audio CDs in this form have never been sold here in EU.

Cheers!

Dear Cat,

I must say that has been a great problem. After I have broken the first CDP I buyed a second one. Now I pulled up everything on the PCB to see more and get more information.  

I asked different Ebay Dealers if I could bid on the same CDP and if I will be the winner they should put out the PCBs and the rest in the trash, because of saving the expensive shipping. They agreed all.

For the first CDP I payed 132 GBP shipping and import tax, for the replacement PCB about 15 or 18 GBP and no tax, because the PCBs have been marked as repair material.

Sorry that you have ruined your CD 33.

KiKo

Hi,

does anybody know where new PCBs from the MHZS Players were sold for changing?

Dear CAT ,

thank you very much!

Can you give me the adress or email or homepage of the place you have got it?

And another question I have to you. All manufacturers in HIFI and Audio have their own homepage. Only MHZS has nothing. I have tried everything.... www.mhzs.com, www.mhzs.hk, www.mhzs.cn and and and.....and all metacrawlers I know, but without result.

Who is the mysterious manufacturer? Is it the Bada company? I think it must be possible to order directly from the factory or not?

KiKo

Hi

I have finished the CD66 , but there is no clock modification yet. This will come later.

At first take a look at the high resolution pics of the PCBs. I have studied them and investigated some weakness of MHZS Players.

Here they are:

Hi Alf,

fine to hear from you!

Thank you for the tip.
Now I will start to arrange and to resize the pics.  Awaiting your comment after upping them.

At first some pics of not assembled PCBs. If you look for a circuit path it will be very helpful. Please ignore the marking.

Hi Alf,

thats right. The CD 66 uses 12AX7 instead of the 6N3. The rest of the circuit is nearly the same. Espetially the Digital board with heater PSU.

Hallo,

nice to see how much guys from different countries are interested in this CDP and forum. I want to thank you for your response!

Here my point of view:

The Digital board is ok, you can increase the performance on classic ways.

I changed some elCaps to Panasonic FC, added some film Cs above the diodes and changed the input Cs of the filter for PSU. Just nothing in particular. After finishing you can add some damping material; here I used a rubber mat from a store which is selling sport articles. In earlier times I used tar-bitumen roof sheeting, but it makes a lot of dirt. Certainly bitumen is better and more heavy, can be well performed on the chassis, but the sand falls out of the bitumen and after a while it doesnt look. The free positions between the small film caps amazed me, so I studied the circuit paths for checking their functions. The conclusion is very easy - there is one high frequence filtering film cap in a line with 2 free places for other small film caps. Finance seems to be the reason for omitting them. Dont worry about that, I have seen it also on other very expensive equipment! The price doesnt matter, the manufacturers seem to produce the first prototypes fully assembled in best quality and on mass production they save their money. MHZS is doing the same........


Of course there is to paint the lens of the laser, you can read it on earlier pages of this thread. On this board there is not so much to do.

Now, the DAC board is a little bit harder. The most intersting things I found out after taking a look on the bare board.

1. The circuit paths are a totally chaos. For example:

You surely remember the 4 elCaps in a row, in front of them the 4 voltage regulators and in front of them the other 4 elCaps? At first it seemed to be so: 1 elCap to 1 volt. reg. and following is the next one elCap. If you believe it you are wrong. This is absolutely different. I will try to write the paths in some pics with an image editing prog.

2. The heater run very hot. The mounted voltage regulators run inexactly.

3. Read: http://focus.ti.com/lit/ds/symlink/pcm1742.pdf, the DAC needs Dual-Supply Operation: 5-V Analog, 3.3-V Digital. You have a cheap 2 Zener solution here, but TI says, you need a separate supply for the Digital input if you want to have a good sound.

You can see the connection diagram on page 25. The important facts here as copy:


"The PCM1742 requires a 5-V analog supply (VCC) and a 3.3-V digital supply (VDD). The 5-V supply is used to power the DAC analog and output-filter circuitry, while the 3.3-V supply is used to power the digital filter and serial interface circuitry. For best performance, the 3.3-V supply should be derived from the 5-V supply using a linear regulator, as shown in Figure 28."

There is no "clean" 3,3 V supply. The 2 Zener near the DAC produce 3,3 V but in a very noisy way. So I redesigned the complete PSU on this board.

4. All electrolytics in signal path have to be removed (4 pieces , see above) with anything you want - or can pay.

5. A new clock is a good thing.

6. Except the elCaps I changed all resistors in signal path and the tube area for better ones. Some of them are non-magnetic Vishay-Dale Mil Spec  CMF-55, but not all, because they are hard to find here and the most powerful are 1/10 W. Furthermore not all needed values have been available. The other resistors are some of 1, 2 or 3 W metalloxide film from Yageo. The empirical formula is not to take lower power rating but the same value. Minimum power is the power of the old resistor.

7. I had one greater problem in redesigning that you maybe will have too. Please read this now very carefully and avoid this problem:

For the DAC I used a Linear Technology LT1584CT-3.3 / 7A linear regulator. This one has a stability of 0.05 %, is very fast and has a constant voltage of 5 %. Costs are 20 USD.

7 A is absolutely to much for the PCM1742, but it was the only one I could get without lead time. Then I made a great mistake. I connected him where the other linear regulator is connected , the LM 317 - on the big resistor 2,2 Ohms 2W near the two cooler. I have done it because I wanted a single path for the 3,3 V. And I thought, that a 5V regulator can share the same input as a 3,3V. After this procedure it got curious. Player has no  more signal! The solder joints seemed to be all right, so I have searched the error for weeks!

.............and then I found it. It was the expensive regulator. It had not 3,3 V on output, it had 3,85 V! But why?

At the end of the big resistor (where the LM317 is connected) there is an input voltage of more than 20V! So the 3.3V regulator and the LM317 share a 20V input? I couldnt believe. At first I thought the 2W 2,2 Ohms resistor is broken and I had a short-circuit. But it was not so. What was the reason?

The reason is that a Linear Technology LT1584CT-3.3 should not be connected on such high input. I found the answer here:

http://www.farnell.com/datasheets/84158.pdf........"input below 7V".

But why has a single 5V regulator (LM317) an input of 20V?

The answer is on the other side of the PCB. The bigger elCap is not only connected to this 2 voltage regulators, no, this cap is also connected to the 7812 regulator on the other side. This regulator produces this voltage only for the delay at the output.

Again studying the datasheet of the PCM1742 I found the answer on page 2:

" ABSOLUTE MAXIMUM RATINGS: Power supply voltage, VDD –0.3 V to 4 V,

and RECOMMENDED OPERATING CONDITIONS:

Digital supply voltage, VDD = 3 MIN, 3.3 NOM,  3.6 MAX. Here is the problem! This DAC dies at 3.85 V input!

The next problem is - by pulling up (slowly and carefully) the cover of the broken DAC the circuits paths were demolished. Between the cover and the chip is epoxy and the chip, the epoxy and the cover are stucked together.

After a longer time I got a new DAC, a new SMD adapter and a new regulator (for 20 USD again :shock: ).

This time I made no more experiments: the 3.3 V regulator I connected directly on the output of the 5 V regulator (on the same cooler of the LM317). The changing of the DAC is really a hard thing and I dont recommend that if it is absolutely not necessary.

The new high precision 5V regulator is a 1,5 A one instead of the old LM317 with 1 A. The heater runned very hot with 1 A, so I searched a solution for it, because I expected now overheat on the 5V regulator. This is a simply 20 W resistor. Pulling out the 2,2R I build in an 6,8R. Now the heater is a little bit cooler, the resistor a little bit warmer. I wanted that the heater is only handwarm, but he isnt yet. At least I added a second 6,8R in serial and an approx. 5R on the other regulator, the 7808 at the top of the pic.

It is a little bit better, but I will take greater values and conduct some experiments. For the 7808 10V input is enough, for the 5V regulator 8V. Its a simple thing to increase the resistors. Better a hot resistor than a hot regulator.

Its ready now! Now its a really good thing! I will try to explain that all with the pics tomorrow.

Have a nice day


Greetings to our new friends, coming to us from Holland and France. I am your neighbour. Coming from Germany. Pics will come tomorrow......

Alf, Blair? What are you doing now?

Hello,

before updating a part of a very huge archive a tip for everybody who has to rearrange and resize pics easily and fast:

http://www.faststone.org/FSResizerDetail.htm

Its free, contains no Adware and no Spyware and is very helpful.

Here the result of this little prog:

Preparing the material for CD66 and the Xiang Sheng 708B Headphone- / Pre Amp

Basically AudynCaps Plus of a german manufacturer, Panasonic FC Caps, Vishay-Dale CMF-55-143 (non-magnetic, military specification) resistors whereever possible, as alternative resistors Yageo, if a value or power rating didn*t have been available.

A little bit of everything...

The tubes and tube sockets are for the headphone amp.

The voltage suppliers: LT1085 is a 5V, the LT1084 a 3.3V, both high precision and very fast.

Details are here:

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1040,C1055,P1278,D2603


Remenber the maximum input voltage of LT1084 is under the reference voltage of the CD66.  A failure at wiring causes the damage of the LT1084 and the DAC!

Some NOS Cornell Dubilier Aluminium foil Capacitors, WIMA MKP-10 Series polypropylene Caps, an OPA Modul with 2 OPA627 (one is below) and some ultrafast sinterglass Avalanche Diodes Vishay BYV27-100 diodes with 15 nsec. in US Military Standard


Datasheet:

http://www.ortodoxism.ro/datasheets2/5/0wg23dl397lgelgw2xxxyeo3lhyy.pdf

NOS Caps have the same problem, the oil becomes hard, but it is a real aluminium foil.

They sound very very good.

such a long foil in that small cap :shock:

Remember there is a mistake: Dont connect the input of the LT1084 with the central input of CD66 (22 V), which comes out of the bigger resistor (the green 2 watts)!



The rest is ok and I hope good to see.

Note: Some of the Pan FCs are soldered with distance to the board. Some circuit paths are only on upper side of the board, so I wasnt sure of making good soldier joints. As a result I soldered and meassured them on both sides separately.

If the circuit paths haves been ONLY under PCB the FCs can be fixed without distance.