It looks like there is something between R334 and C5.. on the first pic..( 2829) Have you seen this?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...
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..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.
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)
Unit connects audio unbalanced.Seems to be working fine except I thought I heard some hum
No.Do I need to start messing with all the small and super small rectangular smd caps?
Is the humming coming from the unit directly? (not in the audiopath) If so, this might come from the powersupply...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.
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?