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

[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.

 

[substance90]

I have the option of buying either a DP4 or a DP4+ for about the same price. Would you guys say the DP4 with the thru-hole components has less need of recapping or are both equally prone to leakage at that age? Supposedly both units are used in pro studios and are currently in good working condition.

 

[Obsoletemachines]

I have the option of buying either a DP4 or a DP4+ for about the same price. Would you guys say the DP4 with the thru-hole components has less need of recapping or are both equally prone to leakage at that age? Supposedly both units are used in pro studios and are currently in good working condition.

DP4+

depends? can you repair delicate PCB with lots of SMD caps. You need a heatgun, gentle heat (the board flexes) remove the SMD caps and then replace - 30-40. Replace 3.3uf SMD caps on CPU board and Power supply board

You also need to lift the 4053 ics near the inputs and remove the 'coke-cola' like substance underneath - thats electrolytic which goes under the large TTSOP footprint 4053s.

Change heatsinks to regulators.

After all that, ensure none of the JFET mute transistors have been damaged causing 'ground noise' leakage into audio lines.

Check the analog board for 'black' on the traces that will indicate how bad the leakage has been allowed to run. You may need to jump some traces.


DP4

Doesn't have the cap issue but the PALS fail. I haven't managed to read the PALS yet - just not had the time.
DP4+ doesn't have PALS (bipolar) instead as a 'gate-array' chip which does away with all that combinatorial logic.

Ultimately, a serviced DP4+ will out last a DP4 but it all depends.

 

[substance90]

DP4+

depends? can you repair delicate PCB with lots of SMD caps. You need a heatgun, gentle heat (the board flexes) remove the SMD caps and then replace - 30-40. Replace 3.3uf SMD caps on CPU board and Power supply board

You also need to lift the 4053 ics near the inputs and remove the 'coke-cola' like substance underneath - thats electrolytic which goes under the large TTSOP footprint 4053s.

Change heatsinks to regulators.

After all that, ensure none of the JFET mute transistors have been damaged causing 'ground noise' leakage into audio lines.

Check the analog board for 'black' on the traces that will indicate how bad the leakage has been allowed to run. You may need to jump some traces.


DP4

Doesn't have the cap issue but the PALS fail. I haven't managed to read the PALS yet - just not had the time.
DP4+ doesn't have PALS (bipolar) instead as a 'gate-array' chip which does away with all that combinatorial logic.

Ultimately, a serviced DP4+ will out last a DP4 but it all depends.

Got it. So assuming the PAL chips are still functioning, the DP4 will be easier to maintain. The seller told me that the only issue is that 2 volume knobs are slightly scratchy. I can easily replace those.

Just curious though, why doesn't the thru-hole version suffer leaking capacitors?

 

[Obsoletemachines]

PALs can go at any time they run hot.
You don't need to replace Gain knobs, just carefully desolder, dissemble clean the wipers. In fact, you rarely move the gain knobs once you have set levels with your mixer - which is why they get scratchy. If you are using the number 1 gain knob with the front panel that gets some action compared to the rest - which are always set and forget.

The thru-hole version uses thru hole capacitors which are not subject to leakage in the same way as SMD caps. Ensoniq used some bad SMD caps and classic Ensoniq inefficient power supply design - remember they were making this to a price point 4in 4 out multi effects for $1500 when the Lexicon PCM90 was selling at $2500 - adjust for inflation. It was a big deal for small studios to have multi-effects for mixing at that time pre-Plugin/DAW and in the era of the DAT. Corners were cut.

Just to give you an idea 30v DC is sent to the regulators on the analog board to drop to 15v so 15v is given off as heat.

SMD engineering at that point, heat, ground planes were in its infancy and the Japanese were better at it. Look at the PCB substrate used by Ensoniq - it has a lot of flex.

The DP4 case is 30-40pc larger, stronger substrate. However, even at this point heat will caused aging effects and the SRAM chips in particular are an old package prone to failure - the DP4+ has the more robust type SRAMs common on CD-roms and so they had to be more reliable.

DP4+ has extra algorithms and bug fixes the updates went to 2.05.

Both machines are great, they don't quite sound analog (by that I mean BBD which isn't analog anyway) nor do they sound digital like a plugin- it's something else, a whole load of character its very David Fridmann very psychedelic.

 

[j.colt]

What are PALs and what can we do about them on a DP/4?

 

[JohnRoberts]

What are PALs

Programmable array logic.... semi-custom digital logic chips, only available from the manufacturer.

and what can we do about them on a DP/4?

I don't know.

JR

 

[Obsoletemachines]

need to read them out and program some more.

 

[j.colt]

Thanks very much! I get it now. I pretty sure I started worrying about PALs in my Ursa Major 8x32 a few years ago too... Would a standard chip reader work? Or do we need some sort of specialized equipment?

 

[Obsoletemachines]

hi again. sometimes you can trick out a 'standard reader' to read chips and you can write to eproms (but they are not fast enough for audio). People fixing arcade cabs have done this. There are even adapters on Etsy for reading PALs as if they were EPROMS.

The best thing to do, if you are worried is drop the temperature on your old gear. Put in fans, they don't need to run fast and can be on the 5v line (don't put them on the audio power rails). There are loads of heatsinks out there, you may even have some in your computer junk.

I'll add photos of the stuff done on my DP4+s in due course to drop the temperatures.

 

[j.colt]

hi again. sometimes you can trick out a 'standard reader' to read chips and you can write to eproms (but they are not fast enough for audio). People fixing arcade cabs have done this. There are even adapters on Etsy for reading PALs as if they were EPROMS.

The best thing to do, if you are worried is drop the temperature on your old gear. Put in fans, they don't need to run fast and can be on the 5v line (don't put them on the audio power rails). There are loads of heatsinks out there, you may even have some in your computer junk.

I'll add photos of the stuff done on my DP4+s in due course to drop the temperatures.

Excellent! I’d like to see this. And yes, all my early digital box are in an open rack with nothing on top etc. I would love to replace the DP 4 PSU with something that doesn’t need to dissipate that much heat. I had a dp4+ once that died after leaving it on overnight lol

 

[Script]

I have the option of buying either a DP4 or a DP4+ for about the same price.

Easier to recap thru-hole. But SMD not difficult with heat gun. PSU in the 4+ is a bit of a PITA.

Heat:
Open rack is mandatory. Nothing placed above for dissipation.

Also consider case depth:
DP4 is 33cm deep.
DP4+ is almost 40cm.
Connectors need additional space.

Both units tend to bend slightly downward at the back for their sheer weight.

If you can, test both units by listening to them. A friend of mine swears the DP4 sounds better. Personally I couldn't tell.

 

[Obsoletemachines]

Easier to recap thru-hole. But SMD not difficult with heat gun. PSU in the 4+ is a bit of a PITA.

Heat:
Open rack is mandatory. Nothing placed above for dissipation.

Also consider case depth:
DP4 is 33cm deep.
DP4+ is almost 40cm.
Connectors need additional space.

Both units tend to bend slightly downward at the back for their sheer weight.

If you can, test both units by listening to them. A friend of mine swears the DP4 sounds better. Personally I couldn't tell.

DP4 is deeper.

To be fair to Ensoniq, in the manual, it does say place nothing above or below. A lot of gear from this era, or just before, used to be good for keeping your pizza warm eg. Eventide H3000, ASR10 rack is nice and toasty too.

A lot of people say DP4 sounds better, I have both, they don't any different. DP4+ has the ability to run at +4, so you can push a mix (probably a group/stem) into it without it getting 'peaky' the DP4 doesn't. Both sample internally at 35khz with 18khz anti-alias on inputs - so sound is getting contoured on the way in and out. It overdrives, crunchy, nice.

 

[Whoops]

Anyone seen this Ebay link from someone selling a service kit for the DP/4+?

https://www.ebay.com/itm/275668061067?itmmeta=01JH1NNJ2RXFDQWRP9654F2SSK&hash=item402f18cb8b:g:3NYAAOSwKyxeL0ia&itmprp=enc:AQAJAAAA4Mxmj+iGvOveHXEBClPb29iJdtFGjiBF3Z7sfI6SaDOlkQccecp+ZZk9viqxEEYJoomnTiMi69Nr01ChXDMuY41F2Qxde9NgHgpVUMn6s5/j8bMULEyFiSSLc+yiRKMaMJRByj+dOGJunFvFQOwo4UbMdKLeOTdQk6RFOr3jWJ6PRwyxhtyVkIyqHsrAT88OUKMYSVy+sN1oBYTzGlpfzxhAaGxdIqF5CWeY3LnJa+tpxyf+UcRTiu/1Zo1omOP6LOk0sppADiFymCvi+3XGoeFZcUi7/RXmM6WFhGQqIe44|tkp:Bk9SR7ah1rWIZQ



What do you guys think about it?
Does the kit addresses the common problems in the unit

Personally, I think it's overpriced, maybe it's just me....

 

[Script]

That is NOT a repair kit. It's strictly a maintenance kit.

But definitely more plausible than previous kits which did not include swapping out all those SMD caps... !

It saves buyers time sourcing parts - in return for high component cost, of course. You and I can do cheaper, but not everybody enjoys sourcing.

___
The SMD caps on the front assembly seem missing. Maybe just not shown. Those leak too.

The pots & encoder alone drive up the cost substantially. Personally, I think they don't necessarily need swapping out (a bit cosmetic). Ideally the pots are set and forget, even if they feel worn.

I'd would love to see bigger heat sinks and replacement jack connectors for that price

___
CAVEAT
But most importantly, once a unit has developed symptoms of cap leakage and starts to malfunction, with lit input LEDs, digital noise, or as bad as a dead channel, this kit won't help save it.

___
Added:
Seller looks like a good source for several things ensoniq (and other). I'd assume they know their stuff.

 

[Whoops]

Thanks mate,
tomorrow I will open my Ensoniq DP/4+ and will check if there's leakage.
I hope it's still good, it has been kept in my parents garage for years and to be honest I don't have a need for it, I'm quite happy with Altiverb and other really good reverb plugins.

Well if there's no leakage in the caps and pcb then it will go on sale in Reverb.

 

[Script]

Sounds like a good plan.