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

[Script]

The only caps I couldn't get are the two smd between the large heatsinks.

And yet those SMD caps are the ones that wanted and needed to be swapped out most urgently on mine..

[I swapped all elcos on PSU too, although they all had measured still fine.]

 

[eling]

And yet those SMD caps are the ones that wanted and needed to be swapped out most urgently on mine..

[I swapped all elcos on PSU too, although they all had measured still fine.]

Aight, I'll get in and swap them out. It's difficult to get the heatsink out!

So with those measurements above, my power supply is definitely acting up? Could the safety capacitors by the AC input be causing this?

 

[ccaudle]

So with those measurements above, my power supply is definitely acting up?

Not likely. Those are the voltages before the regulators, correct? What is the nominal line input voltage for the unit? What is your actual line voltage? And you said that is unloaded power supply, correct?
If the nominal power supply voltage is 115V instead of 120V, and the line at your house runs a little high without a heavy load, say 122V, and the power supply is unloaded, then 24% high isn't unusual.

 

[eling]

Not likely. Those are the voltages before the regulators, correct? What is the nominal line input voltage for the unit? What is your actual line voltage? And you said that is unloaded power supply, correct?
If the nominal power supply voltage is 115V instead of 120V, and the line at your house runs a little high without a heavy load, say 122V, and the power supply is unloaded, then 24% high isn't unusual.

Thanks ccaudle. It's a 240v unit, I'm in the UK. I'm getting 243 at the AC in.

This is unloaded and measurements in the previous comment are from the power supply jumpers - before the analogue board regulators

 

[eling]

Progress: little to no progress. Still got Bad DC offset, Channels 1 & 3 overloaded. Inputs and outputs all acting very odd and mixed up. Noise or silence all the time, and in Condig D (1>1, 2>2, 3>3, 4>4) I get audio being routed to the wrong outputs.

Replaced the TL072 ICs (U6 & U7) near the TDA1541 - found a destroyed trace underneath one. Replaced the 0.1uf caps around them.
Replaced the NJM5465 ICs (U10 & U105) in the 'output filters and pre-mixing' area. Done simply because they looked heat-damaged. Replaced a number of caps around the same area - waiting on replacement 18pf caps until I can fire it up again.

 

[58Glammer]

... The only caps I couldn't get are the two smd between the large heatsinks.

If you remove the big caps, you should get to the small 3,3 µF ones without removing the heatsinks..

 

[eling]

If you remove the big caps, you should get to the small 3,3 µF ones without removing the heatsinks..

I meant the the 0.1 & 0.22 hidden between the heatsinks.

Unbelievably i managed to swap them out last night without removing the heatsink using tweezers and a lot of guesswork.

 

[58Glammer]

And yet those SMD caps are the ones that wanted and needed to be swapped out most urgently on mine..

[I swapped all elcos on PSU too, although they all had measured still fine.]

Do you mean the SMD 3,3 µF electrolytic ones? Or the smaller ones not electrolytic? Do the small ones need to be exchanged as well? I thought only the electrolytic ones...

 

[eling]

Do you mean the SMD 3,3 µF electrolytic ones? Or the smaller ones not electrolytic? Do the small ones need to be exchanged as well? I thought only the electrolytic ones...

I mean the small ones as well. I've swapped every cap on the power - electrolytic and small smd. I've been replacing the small caps on the analogue board as well.

 

[58Glammer]

I mean the small ones as well. I've swapped every cap on the power - electrolytic and small smd. I've been replacing the small caps on the analogue board as well.

I understand you did, but I asked Script about it... As far I understand just the electrolytic caps need to be exchanged as they dry out during the years... You did well spapping the 3,3 µF SMD electrolytic ones on the digital board.. that was really neccesary... as you already mentioned, they looked nasty underneath.. (maybe from leakage). Also the tantalum caps... they don´t dry out, but they have other issues when they get old and can cause shorts when they fail as well.... but the normal non polarized smd caps.... I doubt they need to be changed.
(I forgot about the security caps.. actually you can leave them, but tecs say, if you have it open already and recap a powersupply, exchange the security caps as well as they are for security )

But anyways.... did this change something on the output of the powersupply?

 

[Script]

Yes, all SMD elcos in my unit were bad -- across all boards !

Thru-hole elcos on PSU board measured still fine, but I swapped them out nonetheless.

[I also swapped 0805 (actually all 0.1)... might not be necessary but I was looking for practise]

 

[Script]

I had linked somewhere above to a repair report where noise was caused by faulty 0.1 caps (after exposure to electrolyte).

 

[eling]

I had linked somewhere above to a repair report where noise was caused by faulty 0.1 caps (after exposure to electrolyte).

I read that, very helpful. As my boards have been cleaned up before it's a bit hard for me to tell where there might be hidden damage.

I've noticed in pulling up some some of the 0.1 caps and ICs that there is degredation underneath etc. So I figure it can't hurt to replace them as I go.

did this change something on the output of the powersupply?

Actually not really any change, everything is coming out a bit hot from the power supply and even a bit high after the regulators on the analogue board.

 

[58Glammer]

Yes, all SMD elcos in my unit were bad -- across all boards !

Thru-hole elcos on PSU board measured still fine, but I swapped them out nonetheless.

[I also swapped 0805 (actually all 0.1)... might not be necessary but I was looking for practise]

Thank you! Yes, all elcos should be swapped even if they messure ok. Especially the big ones on the PSU should be spapped. Interesting, you swapped the non polarized smd on the psu (for practice) Did this improve the outputvoltage on your psu? And what ouput voltage did you have in the end on the ouput? Maybe I need to get into the PSU again... I still wonder why they put 30 +- to 15V regulators....
I mean, my unit works fine now... but if there´s a way to not stress the regulators out to the max, I will get into the PSU again if necessary

 

[Script]

Did this improve the outputvoltage on your psu?

I can't tell, cos I swapped all in one go together with dead fuses etc before first power on. Yes, 29-30V from main PSU when loaded.

 

[58Glammer]

I can't tell, cos I swapped all in one go together with dead fuses etc before first power on. Yes, 29-30V from main PSU when loaded.

Man, your unit was so wrecked much respect.
Maybe I should give it a try and change the small ones as well...
This PSU looks like bad designed. Who puts little elcos and other small smd parts under a heatsink behind big caps where you can‘t reach them?
I wonder, there is no alternate PSU for the DP4+
What happens, when the analog V input is fed with +-20 V instead of +-30 ? Are the regulators underperform then or starting to freeze (temperature wise )?

 

[Script]

your unit was so wrecked

And still is...

I will get it off the shelf again eventually. But for now it's good to know it's not 'leaking' anymore.

 

[musgrave]

Coming in late on this thread so I apologize if I repeat information or I’m slightly off kilter… That said, I do a lot of electrolyte leakage on Neve modules. The stuff is insidious. It has a positive charge by nature to make the capacitor have more value in a small space. So whenever it leaks out near a negative trace it will follow the trace. Same goes for logic the toggle between ground and a minus voltage to switch a fet. It also absorbs into the green solder resist on the circuit boards and into the PC board itself if left a long time. This was a couple audio into logic, and couple DC into audio. It also dissolves the traces. I generally have to use an X-Acto knife and scrape the solder resist into the circuitboard away from either side of all traces that are near the contamination. Often I can measure a meg or less of resistance between two isolated traces and as scrape it disappears.
The clues are logic doing weird things and DC voltage on op amps that shouldn’t be. are usually have to replace AC sockets, and if the FETs have the little lake spacers I have to pull those out too. On the worst cases I have to take a Dremel tool and grind with a deep layer of circuit board because I can measure 200 to 300 mV on the green area of a circuit board in between inches. The whole PCB becomes a capacitor. I don’t know if this is your situation, but these are some techniques are used to bring back circuits or the outputs are all sitting on the rails and the logic refuses to work. Best of luck to you. Also I get a little piece of black foam and in the area of a leakage I take out all the parts, resistors, caps, everything and I put them in the foam exactly the way they would be on the circuitboard so I can put them back when I’m done doing the scraping. Cheers have a good week

 

[musgrave]

Coming in late on this thread so I apologize if I repeat information or I’m slightly off kilter… That said, I do a lot of electrolyte leakage on Neve modules. The stuff is insidious. It has a positive charge by nature to make the capacitor have more value in a small space. So whenever it leaks out near a negative trace it will follow the trace. Same goes for logic the toggle between ground and a minus voltage to switch a fet. It also absorbs into the green solder resist on the circuit boards and into the PC board itself if left a long time. This was a couple audio into logic, and couple DC into audio. It also dissolves the traces. I generally have to use an X-Acto knife and scrape the solder resist into the circuitboard away from either side of all traces that are near the contamination. Often I can measure a meg or less of resistance between two isolated traces and as scrape it disappears.
The clues are logic doing weird things and DC voltage on op amps that shouldn’t be. are usually have to replace AC sockets, and if the FETs have the little lake spacers I have to pull those out too. On the worst cases I have to take a Dremel tool and grind with a deep layer of circuit board because I can measure 200 to 300 mV on the green area of a circuit board in between inches. The whole PCB becomes a capacitor. I don’t know if this is your situation, but these are some techniques are used to bring back circuits or the outputs are all sitting on the rails and the logic refuses to work. Best of luck to you. Also I get a little piece of black foam and in the area of a leakage I take out all the parts, resistors, caps, everything and I put them in the foam exactly the way they would be on the circuitboard so I can put them back when I’m done doing the scraping. Cheers have a good week

Sorry about the typos I’m pretty dyslexic… Everything looks good the first two or three reads… But then it doesn’t. lol

 

[Script]

Often I can measure a meg or less of resistance between two isolated traces and as scrape it disappears.

On the worst cases I have to take a Dremel tool and grind with a deep layer of circuit board because I can measure 200 to 300 mV on the green area of a circuit board in between inches. The whole PCB becomes a capacitor

Thanks for the hints. I'll have to check for those. I wouldn't be surprised at all should I find some of that in the unit over here.--