Just out of curiosity: what is the purpose of the variable resistor 3132 (FOCUS OFFSET, 47k) on the Philips C.D.M-1 mechanism? Neither the service manual of the mechanism, nor the service manual of the CD player (Marantz CD-94 in my case) does mention anything about this adjustment.
The only focus related adjustment is just setting the height of the turntable with a Torxx screw until the voltage on the focus motor is 0V +/-100mV.
This variable resistor apparently balances the input offset of the Focus Error amplifier uA741. Would it make sense to disconnect the flex cable from the photodiodes going to the NE5514 preamplifier, adjust 0V on the output of the uA741, reconnect the photodiodes, and then do the turntable height adjustment? In other words, do electrical offset zeroing first (open loop) and then do the mechanical zeroing (closed loop).
The only focus related adjustment is just setting the height of the turntable with a Torxx screw until the voltage on the focus motor is 0V +/-100mV.
This variable resistor apparently balances the input offset of the Focus Error amplifier uA741. Would it make sense to disconnect the flex cable from the photodiodes going to the NE5514 preamplifier, adjust 0V on the output of the uA741, reconnect the photodiodes, and then do the turntable height adjustment? In other words, do electrical offset zeroing first (open loop) and then do the mechanical zeroing (closed loop).
There is no mention of that adjustment nor in the CDM1 SM or in a CD player SM (CD-104 in my case). There is just a check for AGC and offset, so I suppose the focus offset in CDM-1 is not supposed to be serviced, it will be factory set only.
I'm quite hesitant to re-adjust CDM on those old CD players, they typically requires external gig to be set-up and equipment I do not have.
If it works leave it be 🙂
I'm quite hesitant to re-adjust CDM on those old CD players, they typically requires external gig to be set-up and equipment I do not have.
If it works leave it be 🙂
I did a test. Disconnected the flat cable #C06 of the detector diodes and measured the voltage at the focus error op.amp #6107 (uA741). But however I turn the focus offset variable resistor #3132 (47k), there is no change. The service manual shows 0V, but I get a fixed -1.5V. Maybe I made a mistake in this test.
Thanks to @bram jacobse finally I could adjust Focus Offset. As he described here:
https://www.diyaudio.com/community/threads/philips-cd104-tweaks.32591/page-49#post-7693962
The AC voltage at output of the 741 should be nulled out.
I spent a lot of time on this, because I could not null it. At the end I found two reasons:
1. The conductive path of the 47k trimmer was broken at one leg.
2. After having the pot replaced, it still could not be nulled. I checked every SMD resistors, replaced the NE5514 and the uA741, no luck. Eventually I washed the PCB with isopropyl alcohol, dried with a hair drier, and now everything is fine. The old brown phenolic PCB must have had a leak path somewhere.
https://www.diyaudio.com/community/threads/philips-cd104-tweaks.32591/page-49#post-7693962
The AC voltage at output of the 741 should be nulled out.
I spent a lot of time on this, because I could not null it. At the end I found two reasons:
1. The conductive path of the 47k trimmer was broken at one leg.
2. After having the pot replaced, it still could not be nulled. I checked every SMD resistors, replaced the NE5514 and the uA741, no luck. Eventually I washed the PCB with isopropyl alcohol, dried with a hair drier, and now everything is fine. The old brown phenolic PCB must have had a leak path somewhere.
I sometimes use Luminol and a UV lamp on PCBs about which I have doubts, it quite easily reveals a fracture on a track by revealing the fracture line as highlighted.
I also used it on motorcycle frames that have been damaged to visualize cracks caused by the shock.
You can find them quite easily on Amazon, as well as UV lamps.
I also used it on motorcycle frames that have been damaged to visualize cracks caused by the shock.
You can find them quite easily on Amazon, as well as UV lamps.
Can you walk through this process please. Do you coat the whole board with liquid luminol and then just shine the UV light on the board? I am anxious to try this and want to get it right. Thanks.
Actually, it depends on the type of device and breakdown.
I try as much as possible to spread the minimum with a brush without removing the pcb.
if it's really a stupid thing, then I remove the pcb and spray luminol on the entire surface.
And wear gloves, just a tip 🙄
I try as much as possible to spread the minimum with a brush without removing the pcb.
if it's really a stupid thing, then I remove the pcb and spray luminol on the entire surface.
And wear gloves, just a tip 🙄
I have an analog Tektronix scope with the built in, on-screen voltmeter read-out. Sometimes it works, sometimes it doesn't. When it doesn't, the screen gives a message that says something like, "Ouch. Input too high. Please rotate CCW." I have isolated it to one board, and there is a particular section of the board that seems to respond to heat with a heat gum, or pressure with a non-conductive stick. I resoldered all of the nearby joints and verified individual components as much as I can. Still, I have not been able to isolate it further and hoped to use the luminol/UV light method to see if I can see something I am missing with the naked eye.
Based on my situation, how would you recommend I proceed? Also, is there a particular type of luminol I should buy?
Thanks.