Ensoniq DP/4+ (cap leakage, corrosion)

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maxbobo

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The behavior on this is baffling. Bad DC Offset is gone, surprisingly.

I was getting ready to compare outputs of the opamps and just barely tapped on the related trimmer with a chopstick and the white noise went away. so I figured maybe it was dirty/oxidized and wouldn't null dc.

Upon rebooting the error was gone, Ch. 1 green LED was out, unless I cranked the input pot - it would return with a horrible feed-backing distortion. I re-initialized the unit and now I’m right back where I started. Those symptoms cleared up, but: Ch. 1 has a green LED.

I’ve noticed that when the DP4 is switched to -10, Ch. 1 is much louder than the others. I'll start looking at input diff amps and the guitar mic/input pre.

Working on SMD is not so bad… but these cheap rework stations are a nightmare. Mine broke within 30m of use (was continuously heating in the cradle and began to melt). Since this was just caps and not ICs I was able to finish with an iron.

Anyway, it really does seem like a bridge somewhere, maybe to a via under a cap. If I can just figure this out I can give you some straightforward measurements before I rerack it, Script…
 

Script

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Noticed that in picture you posted, there is a cap (C456 in channel 1) on the board. Is that a new one already?
 

maxbobo

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No, I think that was the last of the old ones - before I cleaned up the board. I had waited to remove it because the trace by the pad looked very weak.
 

58Glammer

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Just got the Service manual for mine...
mine is pretty good looking but when I read your thread I was like.. ok, let´s do a recap ;)

I found out,
it is possible to recap the SMD 100µF/16V electrolytic caps with "normal" electrolytic caps. When you remove the SMD version, there are also solder joint/holes where you can install the regular sized ones. (Much easier to install)

On the 3,3 µF/50V and the 22µF/16V it is not possible to install others then SMD.

Best
 

58Glammer

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I removed the caps on the analog board to check for corrosion.

There was definitely evidence that it was beginning, as attached, but every trace I checked out point to point had continuity.

So I went ahead and shotgun approach - recapped the whole analog board. This has solved the problems of peak LEDs lit every time any audio is applied to the inputs, and the outputs of channels 2-4 are quiet.

But now... Channel 1 has a permanent green LED and some hissy white noise when the input is cranked. The unit is kind of usably working though otherwise.

I've still got the digi board and psu to do, but I would guess this is my fault. I've done barely any work with SMD components and maybe damaged a trace or shorted to a via in the process...
It looks like there is something between R334 and C5.. on the first pic..( 2829) Have you seen this?
 

58Glammer

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Ok, today I received the last parts from my distributor.. the 22uF / 25V tantal caps..
After I recapped the cpu board and the controlpanel, I tested the unit on the mixing desk...
And I can tell, it already sounds great without going trough the service manual completely (just checked the voltages) !
I just can recommend, even if you got a unit that sounds good and looks good, if it hasn‘t been recapped since the 90ties , please recap it.
I also recommend to use the right tools. SMD with a normal soldering station might not be the best idea.
 

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Script

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Good idea wrt those 100µF/16V. Also looks better ;)

Those tantalums, yeah, better be replaced too. If I remember correctly, they all sat on the power rails. Some close to regulator heatsinks where they get constantly toasted.
 

58Glammer

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Good idea wrt those 100µF/16V. Also looks better ;)

Those tantalums, yeah, better be replaced too. If I remember correctly, they all sat on the power rails. Some close to regulator heatsinks where they get constantly toasted.
There is one tantalum on the analog board and a lot of them on the digital board. The caps sitting between the hot power regulators on the analog board are the 3,3 uF 50V.. I don‘t get, they put 30 V to 15V regulators and 12V to the 5V regulators..
As you said, the caps between get heat all the time..
A note to the controlboard. Before I recapped this, I had the feeling the display light was a bit low. After the recap, it looks much better now and bright like it should be.
 

eling

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Thank you for sharing all of this Script. I'm hooked, waiting for updates...

and as it happens I have a DP4+ with the following issues:

'Bad DC offset' warning
Ch. 2 failed test - no signal from input, green LED on
Ch. 3 green LED on, faintly audible noise
I've also noticed C99 is missing

I'm really hoping to be able to do a full repair, someone has definitely been inside the unit before me and replaced the electrolytics, maybe the SMD, I can't tell. Some work has also been done to tidy and reconnect degraded traces around the analog i/o also but it doesn't look nearly as well executed as yours. Otherwise the boards are pretty clean, the reverse side shows no sign of damage.

I'm going to start reflowing much of the analog board, checking continuity on traces and taking some multimeter measurements based on what I've read here so far. I don't own a scope so I might be a bit limited in what I can do.

Yet to order any replacement parts. What package size are the SMD components? I'm not sure how to tell.
Any further suggestions?

(images: birds eye view: full, analog, digital, power)
 

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Script

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Package size of SMD components in this unit:

- resistors, small-value caps (all pf and 0.1 bypass) are 0805
- as for the bigger grey 'tombstone' caps, some can be replaced with thru-hole (see above); as for the others, you'd have to measure the footprint and then go find them

Example:
22uf, Diameter 5 mm, Length 5.8 mm
3uf, 4 mm x 5.4 mm
I think, but better measure yourself.

Also need to measure diameters of big thru-hole caps on PSU, should you consider swapping them out.
 

58Glammer

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Thank you for sharing all of this Script. I'm hooked, waiting for updates...

and as it happens I have a DP4+ with the following issues:

'Bad DC offset' warning
Ch. 2 failed test - no signal from input, green LED on
Ch. 3 green LED on, faintly audible noise
I've also noticed C99 is missing

I'm really hoping to be able to do a full repair, someone has definitely been inside the unit before me and replaced the electrolytics, maybe the SMD, I can't tell. Some work has also been done to tidy and reconnect degraded traces around the analog i/o also but it doesn't look nearly as well executed as yours. Otherwise the boards are pretty clean, the reverse side shows no sign of damage.

I'm going to start reflowing much of the analog board, checking continuity on traces and taking some multimeter measurements based on what I've read here so far. I don't own a scope so I might be a bit limited in what I can do.

Yet to order any replacement parts. What package size are the SMD components? I'm not sure how to tell.
Any further suggestions?

(images: birds eye view: full, analog, digital, power)

Actually your board looks pretty good to me (exept of the missing C99). Looks like a nice recap job to me. Have you checked the voltage coming from the PSU?

All SMD electrolytic caps were replaced by normal caps. Not sure, if you need to replace them through SMD caps again... the ones you got istalled might be better.
When you look at my images, you can see the SMD ones I replaced by SMD. The big ones I replaced by normal ones as you can see. But actually it´s better to replace the smd electrolytic caps by normal caps like you got in your unit.
It´s also recommended to renew the tantal caps. you will find one on the analog board (C429 22µF/16V Tant) and a lot of them on the digital board (same value). These brown plastic looking ones with the stripe (in this case +) on one side. (You can see it on my image where I hold the desoldering iron..)

I recommend you to download the service manual and the schematics you find in this forum. Try to get the missing C99 that is a 0,1 µF (you can check the other caps like C138 that has the same value for reverence) C99 btw is in the region on the schematics where channel 2 components are.. so that might have to do with the channel 2 failure ;)

What I found out when reinstalling my recapped unit in the studio, that the audio sounded weired.... like distorted, but more digital distortion...

So there are these DC offset potis on the analog board for each channel 1-4 (it´s written on the board!) where you can adjust the offset.

What I did.... I let audio run through each channel and put the effects on bypass.
Then you can hear the audiosignal without effect .
Mine was distorted as said. I turned the dc offset poti of the actual channel till the distortion was gone. You will need to find the right spot. Then when you turn on the effect again back from bypass, the effect should sounds right :)

Try to do this with each channel.
But get missing parts first !

A question.. if you ran the tests, I guess you already had the service manual, right?
 
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willweb

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This is an awesome thread. So here is my story. As you can see I have no damage at all from the caps. I bought the unit back when it was released and then used it for the better part of 3 years in the studio and it never left the rack it was in.. Then when I moved my studio from Detroit to Miami I got rid of most of my outboard gear and went to working in the box. I have had this unit packed away ever since, mainly because it contains presets that i created and used on some of my early tracks. It is a little dusty but in pretty much perfect shape. I have now pretty much repurchased all the old analog boards that i used in my original studio and have brought the DP/4+ out of retirement. Seems to be working fine except I thought I heard some hum so I unplugged it and started looking up problems people had with the unit. The cap problem seemed to be the biggest problem anyone has had. so before I fire it back up I want to do a full cap replacement. So my questions are. Since I don't have any leakage, should I replace anything other than the big caps on the power supply and all the round electrolytic smd's. Do I need to start messing with all the small and super small rectangular smd caps? Should I replace the larger yellow brick and round tantalum caps? And has anyone come up with a complete list of the parts needed yet or should I just go over to Mouser and start a lookin'. There was also mention of a repair manual, does anyone have a link? I already have schematics from online and the original user manual that came with it, but that's it. Thanks for any answers that anyone has for me.dp4+ 1.jpg dp4+ 2.jpg dp4+ 3.jpg dp4+ 4.jpg
 

58Glammer

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Seems to be working fine except I thought I heard some hum so I unplugged it and started looking up problems people had with the unit. The cap problem seemed to be the biggest problem anyone has had. so before I fire it back up I want to do a full cap replacement.
Is the humming coming from the unit directly? (not in the audiopath) If so, this might come from the powersupply...

I‘d recommend a full recap anyways. As you wrote, you bought it when it came out. These electrolytic caps dry out even when not used. Especially the SMD ones from the 90ties.

Are you good in soldering? If you don‘t use the right tools to unsolder the SMD elcos it could end up in a mess..
You can try to clip them away, but then you risk to rip off solderpads ..
What I did first, before I used the desoldertool, I cafefully clipped off the top of a cap and then took away the rest but leaving the cap’s legs. Then I had better access to the legs and desoldered these one by one.

Did you find the schematics and the service manual here in the forum?

I also saw someone offering a full service pack selling on reverb. But this also included new regulators and other parts I‘m not sure you will need. Did someone else see that offer?
 

Script

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Yes, saw several offers similar to that. Some look like very quick money without having to give any kind of success guarantee...

Buyer beware. Some of those offers are downright deceptive and even ridiculous. Some 'fix' the wrong things while others call themselves upgrades but don't touch the culprit, etc [BTW, anyone has a cap BOM ;) ]

Either way, with those kits need to know how to solder, right -- so personally I'd skip on such offers and DIY it all the way. Thus, better control over components, only get what's really needed, and with some of those offers even save 100 bucks and more. -- Pathetic !
 

willweb

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I probably had a balanced cable plugged in, but I've already got it apart so I'm going to do the recap since its going to need it anyway. I have a full rework station and microscope projection unit. I restore analog keyboards for fun, so I have lots of practice with through hole, but not a lot with smd. This will def give me the practice I need! Some of those kits have new voltage regulators, did anyone here find the need to replace those too? I see a little discoloration on the caps directly under the VR's and Heatsinks on the analog board, so I am going to replace those caps for sure. Found the service manual TY Script.
 

eling

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Actually your board looks pretty good to me (exept of the missing C99). Looks like a nice recap job to me. Have you checked the voltage coming from the PSU?

All SMD electrolytic caps were replaced by normal caps. Not sure, if you need to replace them through SMD caps again... the ones you got istalled might be better.
When you look at my images, you can see the SMD ones I replaced by SMD. The big ones I replaced by normal ones as you can see. But actually it´s better to replace the smd electrolytic caps by normal caps like you got in your unit.
It´s also recommended to renew the tantal caps. you will find one on the analog board (C429 22µF/16V Tant) and a lot of them on the digital board (same value). These brown plastic looking ones with the stripe (in this case +) on one side. (You can see it on my image where I hold the desoldering iron..)

I recommend you to download the service manual and the schematics you find in this forum. Try to get the missing C99 that is a 0,1 µF (you can check the other caps like C138 that has the same value for reverence) C99 btw is in the region on the schematics where channel 2 components are.. so that might have to do with the channel 2 failure ;)

What I found out when reinstalling my recapped unit in the studio, that the audio sounded weired.... like distorted, but more digital distortion...

So there are these DC offset potis on the analog board for each channel 1-4 (it´s written on the board!) where you can adjust the offset.

What I did.... I let audio run through each channel and put the effects on bypass.
Then you can hear the audiosignal without effect .
Mine was distorted as said. I turned the dc offset poti of the actual channel till the distortion was gone. You will need to find the right spot. Then when you turn on the effect again back from bypass, the effect should sounds right :)

Try to do this with each channel.
But get missing parts first !

A question.. if you ran the tests, I guess you already had the service manual, right?

Hey! Sorry for the delayed reply - so good to have your thoughts and thanks for the info about the potis - I was wondering about those!
I do have the schematics and service manual.

I hadn't had a chance to do any fiddling around until this afternoon:
- recapped the powersupply
- replaced C99 on the analogue board
- replaced all of the tantalum caps
- removed the remaining SMD electrolytics on the digital board - they were all quite disgusting underneath. Lost one solder pad but that shouldn't be an issue.

Tomorrow replace the electrolytics and give everything a little clean before putting it all back together to test.

Will the power supply output the expected voltages unloaded?
 

eling

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I'm getting high DC readings from the power supply

Analogue pins from J3:
1: +36v
2: -36v
3: -16v

should be: 1: +29, 2: -29 & 3: -13) according to the service manual.

That's with nothing plugged into the power supply, completely disonnected from other boards. It was booting up fine etc prior to capacitor replacement so unlikely to be anything else going on?

Everthing on the suppy looks fine, fuses are all fine, all caps have correct polarity and are high quality parts (including the safety caps). The only caps I couldn't get are the two smd between the large heatsinks.
 
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