rebuilding and setting up the DAP310

[ke7trp]

I spent some time in the last few days working on my DAP310 processor.  This is a three band expander, compressor, EQ,neg peak limiter, from dorrough.  This one was used in a station in Texas for about 20 years.

Step 1, Order all new LM chips.  They are cheap, About 30 to 50 cents each.  About 40 of them are inside.  Lots of them are bad so just replace them.

step 2. Replace any caps that are bulged.  Lots of 10 UF at 50 volt caps where toast. Its an easy job since the cards come out.

step 3.  The biggest issue with these is loose edge connectors. My solution was to lay solder tracks on the board edges. This was a simple 10 minute process. Now the cards are very tight and the connections are solid.

step 4. Verify all the voltages on the PS and replace, fix as needed.  Turn the main voltage pot WAY down before powering up for the first time.  Adjust for 15.50 volts negative when powered up.

Step 5, Yank out all those 28 volt lamps and replace with LEDs. This removes a ton of damaging heat from the unit. I used three LED's over the meters and two plug in bayonet style LEDs near the large output meter. I rewired the diodes in series. Each diode gets 8 volts now and should run for a very long time.

Step 6, Align the unit.

Step 7, Align the unit again.

Step 8. Align the unit one last time 

I have it working on the bench now.  As I back away from the mic, the unit starts to exand and boost the output, As I get up close or talk loud, The compression kicks in and reduces output.

The last part is to set the pre-emphisis adjustment on the air and to set the peak limiter control for what ever neg peak limiting you want.

So far, Its been running along with no Drop outs.  I can bang on the case with no meters jumping around.   On my unit, there is a NRSC filter added. Its showing me 7 to 10 KC output with incredible sound.  Should be nice and clean on the air!

Here are some pics of this unit and one with the lights out to show the LEDs.  In person, The three left gauges are white and the right output meter is white-blue. Very readable. On the camera, They all look blue.

I have an ultra gain pro that will handle the boom mics and feed to the Dorrough and then to the new transmitter. The second Ultra gain pro output will run the T368.  I am going to also keep my DBX 166XL in line so it has a hard peak limiter so I cant over run the new modulator if a knob gets turned.

C

[K1JJ]

Congrats, Clark.  Nice work.

I once owned a DAP310. It has a very long master alignment procedure - a real bear.    I also had trouble with meter drift. Replaced lots of caps. Still drifted. Maybe it was the chips, as you said.  I finally gave it away to a friend. He sent it back to Durrough for a $200 alignment. It still drifted. He also gave it away.

It was a nice unit in its time (70's) and works well when operating as it should.

Since going with a used Berhinger Ultra-Dyne Pro processer, I'm happy and haven't had a single issue.

T

[ke7trp]

The chips fail because people never set the voltage right. This one had 19 volts out of the box. Hence I suggest they back the voltage down, Then turn it up using a meter.

The biggest issue really is the edge connectors. Once that is fixed, This one calmed down. The meters are 0 0 0 all day, all night.  If they move past zero on its own, Its the resistance of the connector OR the Chip on that card is bad.  the FET bias must be stable. 

Lets hope it works and keeps on working!   Otherwise, I will sell it, They are worth big money on FLeabay.

C

[W2DU]

Clark, your experience shows how much more AMers do in understanding and progressing with the technical side of ham radio than most of the slopbucketeers will ever know or do--the inside of their gear is out of bounds to their knowledge!!

Walt

[ke7trp]

Thanks walt! Thats a real compliment comming from you.  I am a young man still and have a lot to learn!

C

[Steve - WB3HUZ]

I will soon be doing something similar on mine. It's working FB, but every few years I open it up, clean the card contacts and connectors and do the setup. One of these years I guess I'll need to bite the bullet and shot gun the caps.

[ke7trp]

If its working, Just leave it   So far mine has been on 24 hours with no issues.  I am in the process now of adding all the gear to the audio rack. I should have it fired up tonight. I hope and pray there is no RFI. The DAP is riddled with RFI issues. It wont tolerate anything..

C

[k3zrf]

I have a DAP310 and have been using it for years.

When I first got the unit I replaced all the electrolytics and cleaned all the edge connectors. One card socket had a crack in it so needed to be replaced.

All that being done and taking the time to set it up has been working well.......no drift.

[ke7trp]

We spent last night setting up the audio rack. All the gear is in and working.  I have not put the rig on the air yet but plan on doing that in an hour.  The dap is holding steady and working like it should so far.

C

[w3jn]

Clark, that's a good strategy - those old op amps seem to have quite a bit more DC drift than newer ones.

[ke7trp]

They are so cheap, Why not replace them?   Mine seems to be running good now.  Its on the air and working just as it should.

C

[WA1GFZ]

OP amps don't usually wear out but if they are bipolar input amps you might consider changing them over to FET op amps. They work much better around RF. Changing amps with the same part number may not bring better resulats unlee they are damaged.

[ke7trp]

There are something like 40 of them so it would be a mess to change them all out and change the design.  The good thing is that the new chips are in fact better then the 35 year old chips that where in there. This thing is rock solid still.  Working great, Sounding Great and not Drifting a bit.

C

[ke7trp]

Last night the Dap failed.  I had a bunch of hash on the output of the dap over the air. The meters pegged out and the output doubled. 

I just shut the rig down and used the T368 for the rest of the evening. Today, I had some time to look into the Dap, 5 minutes and the dap was out on the bench. I tapped around with a plastic pen and found that banging on the power supply board caused the meters to jump.

I started by cutting the old power cord out and replacing it with a brand new cord. The old one was torn at the grommet.

Next, I removed the PS daughter board and resoldered ALL of the connections on the back. I found several loose parts. The center of the solder mounds whould have the parts leg floating in the center. Resolder them ALL to be sure you do not have a hidden bad connection.

After the daughter board was done, I went to the main power supply board.  I flipped it over and found a bunch of cold or corroded joints.  I resoldered the entire thing from front to back.  This took a hell of a long time but I think its worth the effort.

After the dap was back together, That problem was solved.  After tapping around, I found that the LM301 chips where loose. If you tap them with the plastic pen, you got the meters to snap.  I removed each chip and slightly twisted each flat pin. This made the chips fit tight into the sockets. 

A final test of banging around with the pen and I could not induce any meter jumping. 

The DAP is back in the rack and working 100% again.  It sounds full and clean once again. The Dap really adds a new level to your audio sound and punch. 

I post this in case someone comes along to the forum to find information on repairing and rebuilding one of these things. Take if from me, You need to rebuild each board one by one including the PS and PS daughter board. Do it all now or you will just make extra work for yourself later.  Fingers crossed that this thing is fixed once and for all now! I have now worked on this thing 5 times... I wish I would have completed all this work the first time around!  These things are old and here used and abused. Mine is from 1977 and was in real rough shape.

Clark