• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Refurbing a Dual 604

One last idea. Get one of those cans of Freon that are meant to find a thermal problem [if they are still being made]. Then just wait for the problem to reoccur.
I actually had some spares for your turntable, but tossed them last year, figuring that no one is going to pay me decent bucks to fix such a model. Sorry. I get the oldest Dual rim-drives sent to my work bench, but never one of these things.
Well, boating season will soon come to its seasonal close here. Keep us informed.
 
Next steps is to go to the service manual and check voltages are as expected and then if they look ok to start changing parts. I'll be starting with the two chips on the two boards and perhaps any other electrolytics I can find that I didn't already change.

Been playing it all afternoon now and it only happened in the middle of the afternoon once. It doesn't seem to be heat related because it hasn't happened since even though I continue to use it. Actually playing pretty good at the moment.
 
The first time I was in Florida, John Glenn was taking his orbital flight. Not an available hotel room in all of southern Florida. I was almost five. Next time I was there was 1980. Just as I remembered. Hot and humid. And there are giant water bugs that fly. And alligators in the creeks behind homes. And lizards, rather than house cats, roaming the streets. At least most of the coconut-bearing palm trees lining the avenues had by then been replaced with trees that do not bear fruit. Now I am in my 60s. My grandma was right. It goes too fast.
 
Ah yes. I live in the county with the Kennedy Space Center. Used to work there, but now have other employment in the area. You've got a couple of years on me. I'd have been only 3 at the time and wouldn't have known what is Florida or John Glenn back then. Managed to see old John go up in the Space Shuttle about 20 years ago though.

You are right about the gators. Have a canal behind the house and occasionally see gators in there. The Kennedy Space Center is loaded with gators. Most of the property there is wild. Lotsa lizards around the house. They eat the mosquitoes - just like having toads and frogs up north. Been down here since 1994. Love it.

I'm going to get the replacement chips (555 and 4069) and some sockets and start with that to see if I can tame this beast.
 
The story that I was given about why we schlepped to Florida back then was that my father, who was a carpenter, had been offered to bid on building homes at the center [Coco Beach]. I do not know what to make of this. While he was a good guy who made every one of his customers happy, he was a very small fry in the scheme of things. I know that successful people come up from somewhere, but the story has holes I cannot fill. My mom, who had never fired on all eight cylinders, told me decades later that my dad had won the contract but could not bear to leave his small family to take on the work. This sounds too weird to believe. My dad always struggled to make a decent living. Sad. I loved him and appreciate him more now than all the time I had him.

Back to your anchor. Integrated circuits. Isn't the 555 a timer IC?
 
Yeah. The 555 is an ic timer. I'm sure it has something to do with the spin rate of the TT. I found a thread on VE that Dualcan responded to recommending to change both chips. It's kind of a shotgun approach, but these aren't complicated circuits so I can start there and keep replacing parts until it stops doing this forever.

Lots of houses built near the space center in the early-mid 1960's while the space program was ramping up. I can believe a house building contract. That was a boom time.
 
Well, the good thing about your drive circuit is that when you replace a component, the motor does not then require some sort of impossible circuit pot adjustment. Try balancing the bias on the four coil drive transistors on a 701.
 
Cleaned all the pots and it didn’t help. The problem happened again today - twice. I found one of the transistors was bent over. Looked like it could have been shorting but it wasnt.

Ordered a bunch of parts from DK including the tiny electrolytics, the zener diode, both chips, and some sockets. We will do the shotgun approach and change all the likely candidates when they arrive.
 
I’d like to catch it while it is happening so I could take some voltage measurements. The motor is losing power randomly. I wonder if the house line voltage triggers it?

I’ll change the zener first and run it until it quits.
 
Parts arrived and replaced the zener and that didn't do it, so replaced the four remaining tiny electrolytics. Listening to it now. Will monitor for a few days to see if it happens again.

Got the two different IC's and sockets for them in case it still happens.
 
So I replaced those tiny electrolytics on the motor control board. (Not the power supply board inside the black metal box.) There were three 0.47uF and one 0.68uF cap. They looked like little robins egg blue teardrops. I didn't originally recognize them as electrolytics and had to find the caps by tracing the circuit and looking for the C# on the board under each. The new caps came from DK and look like traditional can electrolytics. So far it's been last night and tonight playing LP's and no problems. I'm going to keep monitoring for problems for a few days.

Separately, I still have some hum in one channel that I can chase next, but incrementally this TT is getting better. I am still looking for the shipping screws and a dust cover (long term). I also haven't installed or used the new stylus yet.
 
Those little blue caps are probably tantalum. Very surprised that the bean counters at Dual spent the extra bucks.
 
Hmmm. They are listed in the service manual as electrolytics. Do they go bad?

I wonder if they used these throughout the production run or if they were what was on hand?

Are they less prone to temperature change or more accurate?
 
Last edited:
Tantalum caps have a mixed history. And, there have been several different wet and dry designs. These days, they are THE cap for SMD. Forty years ago, I do not know how they fared. But they were more costly to produce, as the tantalum is a mined product. rather than paper or mylar plus foil.
Come to think of it, even the older 701 has a few.
 
The wiki on tantalum capacitors says they are electrolytics. They are used in ruggedized applications and cost a lot more than traditional caps. It also says that tantalum capacitors pack more capacitance into a smaller volume. I learned something today.

Well, I moved the caps to a more traditional electrolytic type, but they are rated for a longer number of operating hours and higher temp range (105C).
 
Last edited:
Been listening the TT for quite a few days now and no problems with the speed. I think replacement of the 4 tantalum capacitors on the motor control board did the trick. Here is a pic of what my blue caps looked like. I'm going to declare the speed issue fixed and move on.

Elektrolytkondensator-Tantal-Wiki-P1040343-07-02-18.jpg
 
You must log in or register to reply here.
Back
Top Bottom