[crooner]

Hi Fellas,
I recently purchased a second EAD DSP-7000 MKIII that needs repair. I intend to use this DAC as a basis for some mods I'm considering. My main unit is in perfect working condition.

I'm figuring that having a fully working unit will make diagnostics much easier.

Upon initial power-up the DAC locks on the digital signal and the HDCD light comes on when decoding a HDCD. So it appears the digital receiver and digital filter sections are fine.

However, the unit is completely silent on the analog outputs. No audio is coming out on both channels.

I'm suspecting a voltage regulator for the analog stage. Of the three heatsinked TO220 regulators, one is warm to the touch, and the other two are barely warm. Thinking about swapping them with fresh regulators.

The rectifier and zener diodes are also worth checking.

Any other suggestions?  Since the problem afflicts both analog channels, I'm trying to concentrate on components common to both. This unit uses individual DACs and OP-Amps per channel.

Thanks in advance!

[tonyptony]

crooner, I can't give you any direct answer to your question, but I can tell you that if your own efforts don't work out you can contact Greg Palma at Noble Electronics. Greg is one of the original engineering guys from EAD and now does servicing and mods on EAD gear.

Are you sure that's a Mk.III? I've had a DSP-7000 in all three versions; the Mk.III should have two riser boards which are plugged into the main circuit board. Without either riser board it kind of looks like a Mk.I.

  -Tony

[crooner]

Hi Tony,
Thanks for your reply.
It's actually an upgraded MKIII. It appears to have been upgraded to series II and then series III. I have manuals for all three versions!

If you look closely at the pics you can see two add on PCBs. One for the HDCD chip and another for the PCM63 DACs.
My other 7000 III is a factory model and has a different kind of transformer, an "R" Core, instead of the round toroidal. It appears EAD changed transformers during this model's long production run.

I was listening to it tonight. Man what a sound! Beautiful sounding unit. It sounds so much better than the tubed Lite Audio DAC60 it replaced.

[crooner]

Here are more pics I took of the two units side by side, a closeup of the HDCD decoder and sticker on the custom transformer.

[tonyptony]

Wow, you have two! Nice.

I'm still using my Mk.III (it must be an earlier version because it still has the toroidal transformer). I sent it to Boelen (that was the company Greg and another ex-EAD guy were running before Greg went out on his own) to have it heavily modified. Frankly, it was (and still is) a great converter on its own, but the mods made it even better. I honestly can't see - or hear - any reason to want to go to another converter. At least, not for any rational amount of money.

Back to your problem, how do the regulators on the other unit feel in comparison?

[crooner]

Hi Tony!

Yeah I have two. Seems like I have the DSP-7000 fever right now!

I did some extra diagnostic work last night. I checked some resistances on the diodes and other parts. I measured on both units. No differences. I then powered up both at the same time and waited 30 minutes.

The heatsinks on the good unit were barely warm to the touch, all three of them. The broken unit has a single regulator that appears to run hotter than the others, to the point that the hand becomes uncomfortable after a few seconds.

Therefore, I am positive this is a power supply problem. Since the diodes measured ok, this is either a bad cap on one regulator stage or the TO220 regulator transistor itself that's toast.

I'm going to do a 100% capacitor replacement on the power supply section along with fresh regulator(s). I will also reflow the solder joints in this area which look brownish with tons of solder flux on them. Should work after this is done (fingers crossed!).

Best regards,
crooner

[tonyptony]

Good luck. Hope it goes well. 

While I love listening to my system, today is going to be a very nice day indeed. It's a full day at the Philadelphia Kimmel Center. This afternoon will be a general admission casual event to listen to that fabulous new organ, and tonight is one of the last performances of the season - Mahler! 

I promise not to turn on my own system tomorrow! 

[crooner]

I spent all day doing further troubleshooting on the EAD.

All regulator voltages (as marked on the board) were ok. So it appears all the stages are energized properly. The chips including the D/A converters all get warm, meaning they are being powered normally.

The only remaining shared component I can think of, is the "kill" relay on the analog output. The purpose of this relay  is to short to ground both outputs when powering on or off the unit or switching between digital inputs, thus preventing transient "thumps".

A single relay is used for both stereo channels. When the power is off, I can verify that there is continuity between hot and ground on both analog out RCAs. Meaning they are being shorted by the relay.

The curious thing is that I can hear the relay click when I power the unit. However, no voltage can be measured at the outputs and of course, no sound.

Perhaps the relay can fail and still make the clicking sound....

BTW, the unit uses another identical relay to switch the "de-emphasis" network. I played an emphasized disc, and I heard the relay click. So it appears this part of the analog circuit is working.

The replacement relays are cheap so I'll be ordering a couple.

[crooner]

Hey Tony, I hope the concert was great!

Good luck. Hope it goes well. 

While I love listening to my system, today is going to be a very nice day indeed. It's a full day at the Philadelphia Kimmel Center. This afternoon will be a general admission casual event to listen to that fabulous new organ, and tonight is one of the last performances of the season - Mahler! 

I promise not to turn on my own system tomorrow! 

[tonyptony]

It was fantastic! The organ marathon lasted 4 hours with 4 different organists, each taking a 45 minute turn on the Fred J. Cooper Memorial organ. Most of the selections were pretty good, but two of the players (the second and last) were just great. The last guy especially was killer.

My wife and I spent the in-between time walking a bit through the city and then taking in a nice dinner. After that we went back for.... Mahler's Second Symphony. It was stupendous. I wouldn't consider myself a rabid Mahlerite, but I do enjoy his work. And people can argue if Eschenbach is a great conductor of Mahler. But the symphony itself is so great to begin with, perhaps one of only a small handful of works that holds nothing back, that you'd have to be practically dead not to be able to give a half decent performance! And this was significantly better than half decent. The whole thing was great, some very few moments that could be questioned, but the finish was simply thunderous and well played. The Second is one symphony that cannot be given justice (IMO) to a recorded version. It'd be like watching the Space Shuttle lift off on TV (even High Def) compared to being there in person.

Hoping you get to the bottom of things with that DSP-7000.

[AnthonyP]

Hi Fellas,
I recently purchased a second EAD DSP-7000 MKIII that needs repair. I intend to use this DAC as a basis for some mods I'm considering. My main unit is in perfect working condition.

I'm figuring that having a fully working unit will make diagnostics much easier.

Upon initial power-up the DAC locks on the digital signal and the HDCD light comes on when decoding a HDCD. So it appears the digital receiver and digital filter sections are fine.

However, the unit is completely silent on the analog outputs. No audio is coming out on both channels.

I'm suspecting a voltage regulator for the analog stage. Of the three heatsinked TO220 regulators, one is warm to the touch, and the other two are barely warm. Thinking about swapping them with fresh regulators.

The rectifier and zener diodes are also worth checking.

Any other suggestions?  Since the problem afflicts both analog channels, I'm trying to concentrate on components common to both. This unit uses individual DACs and OP-Amps per channel.

Thanks in advance!

Crooner,

Check for voltage at various locations by the IC's.
on the left side of the picture you see the blue ceramics bypass caps?
probe at those locations, voltages should be 3.3v or 5v.
Check voltage at the optamps if your not sure of the pinouts, look up the spec sheets.
Voltage can be anywheres from - or+ 12-15 volts, give or take.

Check for voltage going to the clock.
Many DAC failures I seen, was just from a dead clock.
This you need a scope to check the output.
I would check this first after simple voltage check.


Part swapping can make you a bit burned out..


Anthony

[crooner]

Thanks for your reply Anthony.
Good suggestion to check for voltages at the IC pins.

One thing I have noticed is that most ICs in the analog section are duplicated for each channel. Therefore, if one fails, the other channel should continue working.

I know the digital section is working because it locks to the incoming signal and the HDCD lamp comes on. I'm guessing a dead clock would prevent the unit from locking to the digital signal.

That's why I'm concentrating on components shared by both analog channels. These happen to be the power supply and the "kill" relay. The regulator voltages are fine, so the power supply is ok.

I'm ordering a couple of relays from Jameco. Less than $2 each. Hopefully this should do it!

[hanguy]

You can probe the input leg (common) of the relay and see if you can see any voltage. If you do, you may try to run a wire from that directly to the RCA to prove that you get signal. Then, it's just a simple matter of replacing the relay if this is the problem.

If there is no signal at the common of the relay, then you can further back track to the analog stage. Does this unit use opamp as output stage? If it does, the output opamps are the next logical place to look, especially the +/-12/15V supplies.

Gook luck.

Mike

[crooner]

Yes, it uses Analog Devices AD841 OpAmps, one for each channel. I checked the voltages on the legs of the regulators on this stage (2 TO220 devices per channel), and they show the correct +/- 15 volts.

I have a feeling the relay is the culprit. The de-emphasis circuit uses an identical type of relay. I was tempted to swap them, but I'll wait until the new relays come in the mail.

I did notice this particular DSP-7000 (upgraded to series III) uses Omron relays. The newer model I have uses  Aromats (now Matsushita). I ordered Aromats from Jameco.

Thanks for your suggestions!

[crooner]

Also, this particular relay is a 5VDC unit. It takes power from the 7805 regulator that actually runs much warmer than the others. A bad relay can increase resistance. causing an extra load on the power supply. This may explain the 7805's unusual heatsink temperature...