Ensoniq DP/4+ REPAIR (cap leakage, corrosion)

[58Glammer]

I think it is needed to ensure the string of digital data is converted and fed correctly into the DAC (sample rate or alternating data points: it's ch1 and ch2 in one string) for correct reproduction. -- Something like that.

And not sure why they call it shaker. Maybe shaking left and right... at the correct rate ideally ?

I changed U29 and renewed some parts. Also checked the input area for Ch1-2 again. No better result. I‘ll pass this unit for now as I have another one here.
I will post again, when I get back to this unit.
(Ch 3-4 works perfectly! It‘s frustrating )

 

[Script]

@58Glammer

Could you do me a favour and measure for me resistor R332 (1004) while it's onboard in circuit but with all cables to the audio board unplugged?

The resistor sits near output 4 and right next to the PCB edge.

 

[58Glammer]

@58Glammer

Could you do me a favour and measure for me resistor R332 (1004) while it's onboard in circuit but with all cables to the audio board unplugged?

The resistor sits near output 4 and right next to the PCB edge.

I measured R332 on 2 boards and dependent on the polarisation of your meter..got the same values on both boards . Plus (of the multimeter) on the left, Neg on the right side of R332 about 122 kOhm and Negative on the left, plus on the right, it measures about 95 kOhm. I guess, there is a diode in parallel.. strange on a resistor to measure different values when you flip the pols of the meter.
Hope, that helps…

 

[58Glammer]

Back on the EBay unit..
I‘m about to re-change the caps in the digital area on that unit to SMD caps. Also in the power regulator area.
By removing the caps I found a 3.3 yF cap I installed, where a 10yF should be installed. It sits at the 2068 amp for Ch1 and the mic input..
That might have caused the distortion.
Not sure yet as I need to put on the new SMD caps in the digital area first before I can try again…
TBC

 

[Script]

Thanks. -- Inconclusive over here.

I suspected that there are several components broken in the audio board over here. So I approached by measuring resistances across nodes and comparing to working unit. This helped find three broken resistors and two broken caps so far, scattered all over the board.

 

[Script]

Digital distortion is what I had on channel 4.

I checked resistances across the 0.1 decoupling caps of the DAC (U2, Sheet 9 of 13). Across one cap it measured suspicious so I swapped it. These caps are C11 to C17 as well as C294 to C300.

Good news:
Channel 4 on my "titanic unit" is now functional without distortion.

Leaves fixing channels 1 and 3, which are both still dead.