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

[Script]

Seeing that, I crave for an ultrasonic bath unit

 

[58Glammer]

Electrolyte accumulated under and between the pins of some logic ICs too might explain faulty channel switching, I assume. Did you have that ? If so might try measuring between traces as musgrave suggested.

Not sure, if I had faulty channel switching.. As grindy it looked under U102 it could be..
I repopulated everything now. As I also removed the working op amp U1 from ch 1-2 I decided to install this to the place where the suspicious op amp U101 was..
I will connect the board and hopefully ch 3-4 will work now.
If so, I just need to wait for the ordered op amp and install it to U1
Fingers crossed !

 

[Script]

So whenever it leaks out near a negative trace it will follow the trace.

Trace between C426 and R286 is the negative V rail to U101? Looks bad in yours -- and very bad in mine .

 

[58Glammer]

Trace between C426 and R286 is the negative V rail to U101? Looks bad in yours -- and very bad in mine .

Thanks for the hint. Just checked them connection and they work.
Now that everything is clean and I know the op amp works I will meassure and trace everything again in that section with the Scope

 

[58Glammer]

Thanks for the hint. Just checked them connection and they work.
Now that everything is clean and I know the op amp works I will meassure and trace everything again in that section with the Scope

Good news! I checked the signal going through the input section and I get the signal till the output of the op amp U101 now.. and no more +15 v on in and outputs of U101. There‘s also no DC offset in the inputsection anymore. ..And even better.. I get a signal on the output (headphone)
Seems the cleaning made totally sense..
Checked all 4 channels on inputpath

But Bad DC Offset is still displayed when I switch on the unit.. It seems to be somewhere else...

The area around U17 looks suspicious.. As there are a lot of elcos around. Maybe I will just take some samples of taking out parts to see what’s underneath and then decide to do the whole cleaning program in that section

 

[58Glammer]

Trace between C426 and R286 is the negative V rail to U101? Looks bad in yours -- and very bad in mine .

I just saw, I replied myself Check above...

 

[58Glammer]

Trace between C426 and R286 is the negative V rail to U101? Looks bad in yours -- and very bad in mine .

I made it today. The unit is working and the DC Offset error is gone. And most important.. it sounds awesome!
After I cleaned the area where the Ch 3-4 Distortion adjustmend pots are and the Ch Offset Pots , I checked all traces and found a broken one at the Polystyren cap C119 (ch3). It was barely visible as it was directly at the solderjoint.
I recommend everybody who has a DC Offset error displayed to check the traces at these four Polystyren caps first. Thanks again to Script for the tips and the help!

 

[Script]

Awesome

I should get back to the one over here.

 

[ccaudle]

My wife claims I collect too much old junk, but something just feels right about keeping an older but high quality design running properly instead of just throwing it in the landfill (or even recycling it for scrap metal).

 

[resyn]

Regarding the hum mentioned here (non-audio hum if I understood correctly): my DP/4+ had a terrible! hum. I "isolated" it to approximately the PSU, decided it was acoustic. The transformer in this unit has (had) a metal clamp, which after assembling the unit was ordinarily screwed tightly to the case. After fishing around I could find no definitive electrical reason for its existence, except: it might be/have been to ground the transformer itself. 1st, not bloody likely, and 2nd, the clamp seemed way too sturdy to be needed for this purpose, so I removed it. A residual hum can be heard but only using a (wait for it) stethoscope. For all practical purposes it is gone. The "clamp's" purpose may have been to stabilize the unit's transformer and prevent accidents during strenuous moving (touring etc). So - happy camper! Still, much material for nightmares thanks to this thread. Lastly: just opened my DP/4+ and looked (again) with a loupe and perfect lighting, and there is no sign of leakage anywhere. Still, it does not look to ever have been re-capped and is almost 30 years old...

PS: check out Don Solaris' epic rebuild on youtube ().

 

[CJ]

Motorola - The works in a drawer...

The wiring and connector issues which made them highly unreliable , I remember working on those monstrosities a few years back. Impossible to fix. Luckily they only lasted about 3 years.

Nice work on the ensoniques! (sp)

 

[Script]

Found and picked up another Ensoniq DP4+ from an electronics thrift store.

When I hit the store, the staff had just finished checking the unit and it wasn't on the shelf yet for sale when I spotted it. The tag said it fully works but there was some "noise cos of a jack input". Well. So we hooked it up and it indeed still worked. Then I asked whether I could open the unit for inspection, which was no problem with them whatsoever (maybe because I am a regular there) so they lent me a screwdriver. I used my phone camera with highest magnification (which is really not good enough to see all the details, but still....). After about 15 minutes the staff started to get a bit nervous

I then told them that the unit urgently needs maintenance cos there are clear signs that the caps were starting to leak. Their reply was that they hadn't inspected it THAT closely but only checked whether it still works. To which I replied, "Yes, for now. But are you willing to give me a guarantee should I buy it?" -- Anyway, no guarantee and after a little more talking I bought the unit.

So now I have two DP4+. I call this one UNIT B.

 

[Script]

UNIT B -- Maintenance work


Unit is fully working, but there is strong suspicion of pending cap leakage and a few indications of actual spilling. Another indicator, I think, is the display, cos when changing program, the display went dark and took a bit of time (half a second?) to slowly light up again.

Either way, in general, I'd think it's not a good idea to have the unit powered on (for too long) in this state as it might make things worse.


- DISASSEMBLY
Taking the unit apart is a quick process of just 20 minutes. Careful with the ribbon cable connectors. Never pull on the cables -- instead use a scribe or screwdriver to gently push them up.

- PSU
Changing the five big elcos and two SMD caps is easy enough.
(Took me 1 hour including disassembly and thorough cleaning of PCB afterwards.)

- FRONT PANEL ASSEMBLY
Only three SMD caps here. One showed clear sign of leakage -- some liquid spill close to one cap on PCB. For good access to C2 and C4, one could desolder the leads of three LEDs to take out push buttons S11 and S12. (Took me 2 hours in total cos I also decided to redo a flimsy cap pad with wire.)

 

[Script]

-- UNIT B, Digital board --

Corrosion on eyes.



The next cap is 30mm away ! Not sure, but could be just corrosion due to condensation. Either way, scratching revealed that the eyes are fine. Same at another spot.




Needs 'just' cleaning. Could touch up with solder but probably not essential, I'd think. Most other solder joints across entire PCB are shiny as should be.

 

[Script]

-- UNIT B -- Some clear and some more difficult to spot signs of cap leakage

If you see any of these on your Ensoniq PCBs, stop using the unit immediately and prep for a recap.


Copper rust or leakage ? Either way, needs attention. Cap looks fine, doesn't it. Probably isn't.




More copper rust? Spillage.




Scraper pointing to a drop of spilled electrolyte. Cap 'looks' fine, but pretty sure it isn't.




Several signs of leakage. Used scraper to smear the drop close to 0.1 cap.




And no comment on this one. Obvious. Interestingly, the unit is still functional.

 

[Script]

Dried up electrolyte spots after removing caps with hot air gun.




Gunk looks familiar ? Those drops of liquid were spilled electrolyte.



The removed 3u3 caps measure only between 1u5 and 1u9. One measured 2u6, another only 28p ?? (but might be a measuring mistake).

 

[Script]

And off go those SMD caps on their final journey to where they belong...

 

[58Glammer]

Dried up electrolyte spots after removing caps with hot air gun.


View attachment 106583

Gunk looks familiar ? Those drops of liquid were spilled electrolyte.

View attachment 106584

The removed 3u3 caps measure only between 1u5 and 1u9. One measured 2u6, another only 28p ?? (but might be a measuring mistake).

Awesome! Hope you got a really good price for the unit
The unit looks good! And the leads doesn‘t look so damaged yet.. so you rescued the unit from slow dying . I had a Drumsampler on the table and on one of the two PSU boards with a leaking cap you could see that the electrolyte already did it‘s work. The broad lead was already black underneath the lacquer (that came off by just touching it with a cotton swap) .. The clearest sign for electrolyte damage. I scratched off the sticky electrolyte to the shiny copper, cleaned it again with pcb cleaner and then isopropyl alcohol and then tinned it and sealed it with laquer.
The diodes on your pics look crazy.. might be one of the sources for the noise.. But that doesn‘t look like electrolyte damage to me.. it looks so rusty and grimy .. I would love to see how it looks underneath the diodes.
Looks like you found the unit at the right time.
The unit you originally worked on was/is the absolute extreme!
I still wait for the op amp for my latest unit that had these broken leads at the polystyrene caps. But beside of that it works great now.
Don‘t forget to adjust the distortion pots. If they are not adjusted right, you get subtle noise as well.
Just put a low audiosignal on, set the effects on bypass and adjust the pots till you hear the clear audiosignal. Then try the audio signal even lower.. If it‘s still clear then, the pot is adjusted right.
Congrats on the new unit!

 

[Script]

UNIT B -- Digital board finished (for now)

All new elcos in place. Board cleaned. Eyes retouched.

Here's the dirt spot again, before and after.


There was a lot of electrolyte under the diodes CR1 and CR2 (top of image).



For cleaning the area , I took off all components between this cap and the also leaked adjacent one (almost 30 components in total). Diodes lost their color marking in the process. Everything measures fine in place. Also took components off for cleaning in other areas.

(Only the battery and the tantalum power caps still need swapping out. But that's easy enough and will be done later. Need to order the tants first anyway.)

 

[Script]

The diodes on your pics look crazy.. might be one of the sources for the noise.. But that doesn‘t look like electrolyte damage to me.. it looks so rusty and grimy .. I would love to see how it looks underneath the diodes.

Q21 and Q22 are non-exotic 2N3904 transistors. All components in that area were wet underneath. Looks like rust but was gooey and starting to crust.

Electrolyte eating vias seems advanced stage -- but fixable. And electrolyte soaked into the PCB substrate is cancerous, like in my Unit A -- haha.

Good thing now is that, once Unit B is refurbished and still functional, I could swap boards between units for narrowing down faults.