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

[Script]

Set out replacing all not-yet swapped out dual op amps on the audio board today. And as I thought, it made no difference.

Ch 1 dead
Ch 2 fully working
Ch 3 dead
Ch 4 working but distorted.
Outputs all work fine.

Noticed that a resistor R296 on input 4 was broken. Don't have 9k31 so I hacked in parallel (16k || 22k). The two resistors rest sandwiched on their sides towering up. A bit tricky but doable.--
Makes me think there might be more broken components across the board.

 

[Script]

Briefly checked signals before and after the styro caps. They look the same on scope across all channels. Was quite sure the problem isn't there.

Also swapped some HC4053 around, including U4 and U5 -- unit behaves the same, no difference.

So next step is to check the AD converters. Idea is to place them in working Unit B. Got one out without damage to the board...

 

[58Glammer]

Briefly checked signals before and after the styro caps. They look the same on scope across all channels. Was quite sure the problem isn't there.

Also swapped some HC4053 around, including U4 and U5 -- unit behaves the same, no difference.

So next step is to check the AD converters. Idea is to place them in working Unit B. Got one out without damage to the board...

Wow! That‘s some progress! Have you checked, if you got all connections? Good, you got the signals on the polystyrene caps …
Are the AD converters the big Sony ICs? I put them into sockets…
If they are broken, are there replacments for them to buy?

 

[Script]

U29 (74HC86 and the two J111 J110 are fine too, hmm.

Yes, the AD converters are the Sony. Rather unobtainium.

Doesn't feel like progress. ...

Swapping out a few components or transfer from one unit to another is easy and quick enough. But need time -- which I don't have -- to check systematically.

 

[Script]

Checked for connectivity thoroughly at a very early stage. Guess I have to do it again, this time injecting signals. But before I spend all that time, I want to know whether the converters themselves are OK....

 

[58Glammer]

I recently bought another DP4+ unit for a decent price.
But this time some components are missing.
Knobs and what my question is about, JFETs in the output section
The schematics say J110 Sot23.. Can someone tell me a equivalent part/model/company available I can order at mouser or somewhere else?
Thanks!

 

[Whoops]

The schematics say J110 Sot23.. Can someone tell me a equivalent part/model/company available I can order at mouser or somewhere else?

Use the Links provided in this thread to find equivalent JFETs:

https://groupdiy.com/threads/useful-transistor-equivalence-cross-reference-websites-list.84850/

 

[58Glammer]

Checked for connectivity thoroughly at a very early stage. Guess I have to do it again, this time injecting signals. But before I spend all that time, I want to know whether the converters themselves are OK....

Hi Script, happy new year! (To you all!)
Most of the components are pretty robust. Except they get fried badly.
As some of your channels work, I bet the Sony ICs are ok. On the units I had on the table, I extracted all of them to get rid of the electrolyte underneath. Then I put them into sockets. And I swear, they where set on heat so that I expected to frie one of them… But.. all of them survived …
As you got the right signals on the Styros this section seems to be ok…
It must be something in the audiopath.
First check all audiopaths in the inputsection. If you got all channels there, you can continue with Ch1 that goes to the section U34.. It then goes into the frontpanel and then back .. Ch1 shares with the mic input. Check U35 what is a 2068 amp.. (I had a broken one here)
From there the signal goes to the area around U25… This complete section unlikely has problems as there are no elcos around there… Don‘t forget to turn up the input pots on the frontpanel.. otherwise you won‘t see a audiosignal in that area…
The section around U20-23 should be ok as well from the beginning as there are no elcos there.
Then you got your digital section in the middle.. As you wrote.. Signals at the styros look good.. This section seems to be ok as well.. (You should see the audiosignal within the signal of the upper con of the styros )
Another tricky section is the one on the right arround U3 to U9. If there is a problem, you might not hear audio from certain channels as well.
Check this area for faulty opamps. I check the audio mainly with headphones. As soon I hear all channels there, I check the output section that leads to the ouputjacks.. as last step.
The Digiboard is another story. But you wrote it is ok. As there are not that many elcos there, there is mostly no problem.
Also, if you extracted a lot of caps and resistors, check if you did not mix up components. I just found a mistake I made on the unit I had from Ebay for a nice price and I
mixed a cap with a resistor arround U37 (part of the digital section on the analog board) that caused the unit to display a unexpected error at startup…
Unit is working now, but I have not checked it completely. (See next post )
Also don‘t forget to exchange the elcos in the frontpanel.

 

[58Glammer]

I found time to get back to the unit I had from EBay. It was in really bad condition. Black traces all over the place. Digitalboard was ok after cleaning and recapping.
After cleaning all areas with electrolytic caps from electrolyte I got a unexpected error at startup.
After reinspecting the board today I found out, that I mixed up a resistor with a ceramic cap in the section related to the sony chips in the middle.
After correcting this the unit started up, but with a DC offset error.
The affected channel can be located by testing the styro caps. Signal there is more flat then on the other working styros. It was Ch 2 caused by a faulty 4565 opamp U16 that is shared by Ch1-2.
I see inputsignal on the frontpanel now, but got no ouputsignal yet.
But so far so good. Will check the area arround U3 now. TBC

 

[58Glammer]

Update (EBay unit) Checked the area around U3 till U9 and found faulty opamps. After replacing them all, the audio comes through on all channels. BUT Ch1-2 got a weird distortion that I can‘t really adjust with the distortion and offset pots (all channels put on bypass on the frontpanel). The signal is clean in the area that goes to the Sony IC U55, but sounds weird arriving at U3 (pin 7)
Channel 3-4 work perfect now. And the audiosignal sounds good on all opamps it passes in the U3 area.
Ch 1-2 sounds distorted on all opamps in that area.
My question is what the source is the signal comes in at U3 pin 7? I don‘t really understand it from the schematics.
TBC
I have not checked the audio signals at the output jacks area yet. All checked via headphones, scope and a little jbl speaker used like the scope.

 

[Script]

Maybe other mixed up components ? I tend to never take off too many at the same time for cleaning underneath.

 

[58Glammer]

Maybe other mixed up components ? I tend to never take off too many at the same time for cleaning underneath.

I will double check again for mixed components. Good is, Ch 3-4 works 100% now. So I can compare components. I always take them off in groups. As many as I got pockets (actually for screws) on my blue map Like in the pics here.
I already double checked the area around U103. I thought maybe I mixed R270 as it looks different on ch 3-4 . The opamps in that area are all new. And the distortion comes on both ch. 1 and 2 . I swapped the Sony ICs and same behavier.
Digi board is ok as well as I swapped with another one. I suspect something digital on the analog board. But don‘t know where to look yet. Signals around the U55/U17 look good so far. Maybe U37 got damaged from the component mix.. Or can this be caused by U29/U30? TBC

 

[Script]

U3 pin 7, you mean op amp output...? Not sure.
#

Maybe not related to the noise you hear, but I had at least one broken resistor and one broken cap on one of the boards here. Probably still a few more on it.

 

[58Glammer]

U3 pin 7, you mean op amp output...? Not sure.
#

Maybe not related to the noise you hear, but I had at least one broken resistor and one broken cap on one of the boards here. Probably still a few more on it.

Actually U3 pin 7 is the output of the opamp, but there is not a signal on one of the inputs 5/6 of this opamp.. so my question is where the signal on pin7 comes from? I got, that pin 7 is related to Ch 1-2 and pin 1, the other output of this opamp U3 is related to Ch 3-4 (clean sounding signal here) These pins are somehow connected to TDA1541 AR and AL, but I can‘t meassure nothing with the scope there… I will make a screenshot from the schematics from that area to show what I mean. The problem is, that I actually don‘t understand what‘s technically happening in that area around U3. ..

 

[Script]

Datasheet says AOL = analog output left.

https://pdf1.alldatasheet.com/datasheet-pdf/view/19212/PHILIPS/TDA1541.html
CR70 and CR71 are fine? They sit close to a leak-prone cap. Maybe swap out for new ones (5D).

 

[58Glammer]

Datasheet says AOL = analog output left.

https://pdf1.alldatasheet.com/datasheet-pdf/view/19212/PHILIPS/TDA1541.html
CR70 and CR71 are fine? They sit close to a leak-prone cap. Maybe swap out for new ones (5D).

Yes, analog out Left/Right .. but there is no audio signal to measure… directly on the TDA ..
I suspected the components in that area as well.. they all measured fine, but I will exchange all the components on the left side of U3 just to get sure. I will report if it has some effect. Strange is (what I don‘t understand in the circuit) that the TDA has Right and Left analog out. One is for CH1-2 the other works for CH3-4 .. and I don‘t understand what it does in the circuit as there are actually 4 channels and not just left and right.

 

[Script]

Yeah, this unit is full of non-standard and/or precision-resistor values...

 

[Script]

U29 is good?

 

[58Glammer]

U29 is good?

U29 was one of the next parts I wanted to check. What influence does it have on the audiosignal? I have a spare one that I will try. ..

 

[Script]

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 ?