Help please: Harman HD740 pickup trouble

[hiwiho]

Dear fellows,

on my second set of audio components - attached to my computer - i run an end90's Harman Kardon HD740. It's a midrange player, well equipped with descrete analogue stage and one pcm1702 per channel. The drive is from Sanyo, it's a SF-P101 in 8/5pin version.

I used the player quiete often, and it started to skip and took a long time to read the toc until finally the laser gave up. So i cleaned the lens, but it didn't help. I bought another original and complete pickup (incl spindle drive), put it in, removed the solder bridge and put in a cd-r. It took about 10seconds until it had read the toc. Tried another cd-r.... no reading of toc at all. Took an original disc and it worked quick. I put some tape on the spindle to challenge the focus - no change. Strange that, when testing with cd-r, the player nows the number of tracks significantly faster than it shows the play time and gets into "ready to play". The focus itself seems to happen relatively fast, but then it spins and spins.

I plugged the rca's in... the original disc plays fine. Cd-r, if recognized at all, have a high amount of crackle during the first ~15mins that seems connected to both level and higher frequencies of the music. During those minutes, the crackle gets less and less and skipping to next tracks gets faster and more reliable. Once i leave the crackle behind, it plays just as it should do....

Concerning my experience with swapping pickups (kss210 & 240, vam 12xx) i'd say there's something wrong with focus&tracking gain/offset. But the Harman has no adjustments points except laser power - but i don't want to grill the laser!

Did i get a maladjusted pickup?

Can someone tell me how to enter service mode? Has anyone experience with this type of player (it's as rarely mentioned on google as the sanyo pickup) or laser unit? Anyone willing to share the service manual????

Kind regards,
Matthias

[Extreme_Boky]

You will NOT burn the laser. Just increase the laser power a bit and all your problems will go away....

I am not sure what's with all the DIY-ers who are so afraid to increase the WRONGLY set laser power on (in particular!) SANYO CD drives... It must be some sort of cult… they are reluctant to increase the power even on the OLD mechanisms… probably afraid the laser will burn the whole in their CD’s or something…

I routinely find that SANYO CD drives have 20-30% less laser power than required (measured, tested, proven...)



Boky

[hiwiho]

Boky,

thanks for your encouraging answer.... unfortunately it doesn't help
I re-opened the player,marked the laser pot's original position (which was around 10am) and tested a cd-r that i found it was just capable to read after some time. I turned the pot to 12. no change. 3pm... slightly faster recognition, but still crackling exactly as much as before. 4pm - no recognition anymore, disc turning like crazy.
So i put in an original. It started being recognized at around 9am and played with some crackling. I turned it to 11 and gave up.

So even if i maximize laser current, the burned cd doesn't play correctly. And how come that after leaving the inner tracks, it plays fine? That should not be connected to the laser current but to the tracking...

So what do i do now? Buy another pickup ??

Matthias

btw: i error-checked the burned disc with my computer - it's got less than 80 c1-errors and is an excellent burn

[pupsik46]

OT. Anybody have Harman Kardon HD760 service manual?

[Mooly]

Hello, You say original discs O.K. ? Your CD-R,s may not be being burned correctly, a computer "combo drive" is much more forgiving than many dedicated "cd read only pickups".Try some discs burned on another pc to check.A 'scope check of the R.F. (eye pattern) of the signal coming of the disc would be very revealing.
Regards Karl

[Extreme_Boky]

Originally posted by hiwiho
Boky,

thanks for your encouraging answer.... unfortunately it doesn't help
I re-opened the player,marked the laser pot's original position (which was around 10am) and tested a cd-r that i found it was just capable to read after some time. I turned the pot to 12. no change. 3pm... slightly faster recognition, but still crackling exactly as much as before. 4pm - no recognition anymore, disc turning like crazy.
So i put in an original. It started being recognized at around 9am and played with some crackling. I turned it to 11 and gave up.

So even if i maximize laser current, the burned cd doesn't play correctly. And how come that after leaving the inner tracks, it plays fine? That should not be connected to the laser current but to the tracking...

So what do i do now? Buy another pickup ??

Matthias

btw: i error-checked the burned disc with my computer - it's got less than 80 c1-errors and is an excellent burn

Okay, you've just posted more details and I'll try to help.

First would be to check the circuit diagram and see if the mechanism is used in "over-scanning" configuration, i.e. the low reflectivity disks are detected and the RF out signal kept at sufficient level for servo to work properly.

Some CR-R's have EXTREMLY low reflectivity and can not be read-out properly.

Find the test-point on the PCB, next to the servo section, labelled "RF" and check the amplitude of eye-pattern signal. Adjust the laser pot on the pick-up for around 1.5V pp with high reflectivity disks - those original music disks you buy from the shop. Now, insert the CR-R and see if the CD player behaves the same. If not, you may have a servo issue as well...

Who's the servo "chipset" manufacturer - are they Sanyo chips? In case they are, 1.5V pp value can go even higher, to around 1.7V pp, but not higher than this. 1.7Vpp with good reflectivity disks will give you around 1.1Vpp with low reflectivity disks - just enough! However, this only applies to SANYO servo chipset. With other chipsets / drives the value is much lower, at around 1.0V pp

Either way, the Service Manual will have the exact values needed for a proper operation.

You are saturating the servo section at the moment - you will definitely need to find the circuit diagram and RF test point. You'll also need the CRO.

Cheers,
Nick

[hiwiho]

Originally posted by Extreme_Boky
You'll also need the CRO.

Thanks for your attempts to help. I'll first have to find my scope's cables and will be back tomorrow evening!

But what's a CRO?!?

The drive seems to be from Sanyo, too. The DSP is a LC7821, the ASP a LA9240M. The servo IC has a soldered heatsink on it. Digital filter is a SM5843.

Maybe i should buy the manual. It seems i have to do that with every component i own



matthias

[Leolabs]

Search on some old 40 to 52x CDROM,u may have the luck to see SF-P101 inside.

[Extreme_Boky]

Originally posted by hiwiho


Thanks for your attempts to help. I'll first have to find my scope's cables and will be back tomorrow evening!

But what's a CRO?!?

The drive seems to be from Sanyo, too. The DSP is a LC7821, the ASP a LA9240M. The servo IC has a soldered heatsink on it. Digital filter is a SM5843.

Maybe i should buy the manual. It seems i have to do that with every component i own



matthias

CRO stands for Cathode Ray Oscilloscope. Digital oscilloscope will do as well.

The chipset you mentioned is Sanyo, LA9240M is servo controller and RF demodulator / amplifier.

On LA9241M pin 41 is RF test point / RF OUT. You will have to obtain the service manual to check the pin outs on LA9240M. The proper eye-pattern amplitude you need to obtain, with good reflectivity CD’s, is 1.5V pp.

Boky

[hiwiho]

Boky,
it's pin41 at the 9240m, too. But unfortunately the chipset features some automatic gain control - it doesn't matter how i turn the laser current, it's always 2Vpp at pin 41. The pattern colapses just when the drive doesn't recognize any disc anymore.

Then I remembered a friend had the same player, grabbed my Hameg and i opened the friends Harman. 2Vpp at pin 41. I implanted my drive and had the same sort of misbehaviour

At home i tried the last i could do and replaced the ribbon cable of the new laser with the one of the old - just in case the ribbon was broken. But it wasn't.

I guess now it's the second time i got a defective laser from this crappy shop here - i won't go there again but will order online from well reknown distributors in the future. Rather pay shipping than pay for waste and twice

Thanks for your thoughts and patience!

matthias