Speed Issue - Sansui SR-838; Help?

[kbuch8586]

New update. This thing is a pain! Replaced all transistors and caps. Replaced trim pots. I thought I finally fixed it, but the speed still fluctuates for half a second and then recovers every few minutes. Seems like it's getting worse. Should I try to replace the IC chips in the PLL Servo circuit??? Or should I go over all the solder joints?? That seems like a lot of work, but if it fixes the problem I'm up for it!

If I try to replace the IC chips, does anyone know how to get them? Looks like the part numbers are msm5810 and msm4069, manufactured by OKI.

 

[dankik]

What causes you to believe that those ICs are bad and that you need new ones?

• MSM4069 is a CMOS hex inverter equivalent to a CD4069UB. If one of the 6 inverters were bad, the circuit would not work at all.
• MSM5810 is a MOS LSI Phase Locked Loop containing an oscillator, counters and a phase comparator. I don't know of a modern pin compatible equivalent. Were you able to adjust to get the waveform shown in Figure 2?
• The functions of the 5810 are:

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Here are the instructions in the SM. It says that you need to complete these adjustments when replacing capacitors, resistors, and ICs. Did you do this?
Since you went ahead and replaced "all transistors and caps and trim pots" Did you do all of the adjustments below?

Please post a photo of the oscilloscope screen shot when you adjusted it, or if you didn't use an oscilloscope and if you were able to adjust when the Quartz switch is OFF.



If you changed any of the parts listed in A, then you need to adjust these VRs.



One more thing to check is that the MSM5810 has a speed sensor input on pin 15. If it is faulty, it could be providing bad information to the speed control.
Attach a scope probe to this pin and see if there is anything interesting happening to pin 15 when you have this speed glitch.

If you haven't already done so, check to make sure all of the voltages around IC71 are like on the schematic.

 

[kbuch8586]

Thanks for taking the time and offer these suggestions. I calibrated after installing new capacitors, but then I never went back and calibrated again after installing the rest of the transistors. However, I followed the directions for calibration using a multimeter and it was spot on, 1.4 volts, and able to calibrate with quartz lock off as well. I looked at all the voltages highlighted around MSM5810 and everything checked out except pin 9, which was 2.35 volts instead of 3.2.

I haven't hooked the oscilloscope up to pin 15 yet, but I'll try that next.