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Overhauling a 9090dB

dr*audio

dr*audio

Fish fingers and custard!
When you overhaul a 9090dB, there are a few areas that so far I have found it difficult to access; the board with the speaker relay on it, and the regulated power supply board. I have discovered a trick to get to these areas very easily and will share this info here.
The assembly on top, containing the tuner, IF board, display, and regulated power supply, comes off in one piece. You remove the front panel, remove 8 screws from the top assembly, and you can flip it back out of the way. Then you can access these boards. Once you do this, the following things need to be done for every 9090dB:
1. Resolder the joints on the regulated power supply.
2. Tighten the ground screws on the IF Board.
3. Replace the speaker relay. Do NOT try to clean the contacts, it will only work for a short time.
4. In this receiver, the speaker jacks are shorted to ground when the relay turns off. Sometimes the relay contacts weld themselves shut and short the poweramp output to ground when the relay turns on. Remove the jumper wire on the relay board that goes from the relay contacts to ground. It is just to the right of the relay, right next to it.

wbendler56
 
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Thanks for the tip! Other amps that i've noticed do the same 'tuner off in one piece trick' are the Sansui QRX-777/7001 and the Yamaha CR-1000.
 
dr*audio said:
Remove the speaker relay and burnish the contacts, and clean them.
4. In this receiver, the speaker jacks are shorted to ground when the relay turns off. Sometimes the relay contacts weld themselves shut and short the poweramp output to ground when the relay turns on. Remove the jumper wire on the relay board that goes from the relay contacts to ground. It is just to the right of the relay, right next to it.

wbendler56
Click to expand...

Is the 9090 the same way? I'd hate to think about my finals being shorted to ground, for any reason. :yikes:
 
Other stuff that needs to be done to every 9090dB during a rebuild:
Resolder all the feedthrus on the Dolby board.
1. Check the flat flexible cables on the Dolby board for intermittant connections and replace them if necessary.
2. Clean all the controls, especially the function switch.
3. I like to replace the meter lamps with high output LEDs, because they are a PITA to change. Also when I do this, I replace the short wires that connect to the meter PCBs with longer ones to make them easier to service.
To change the lamps to LEDs you need to add a 1N4007 diode in series with the meter lamp supply voltage, and a 1000uF cap from the cathode of the diode to ground. Then replace the resistors on the meter boards with 68 ohm 1/2 Watt resistors to limit the current through the LEDs. The 2 LEDs on each meter must be installed in series. It's a bit hard to describe how to do this but it is easy to figure out with the meter board in front of you.
 
Warren:

Great info and since I have those LED's waiting for insertion into the Project 990DB it's very timely too!

I will add the thread to the FAQ's.

Paul
 
Thanks, Paul. I should have mentioned that the 68 ohm resistor works with this LED from Marlin P Jones:
http://www.mpja.com/prodinfo.asp?number=12567+OP
Different LEDs have different voltage drops so you should check the voltage drop across the resistor and divide by the resistance to get the current. It should be no more than 20mA. With these LEDs, the current is 15mA, which is perfect.
 
dr*audio said:
Thanks, Paul. I should have mentioned that the 68 ohm resistor works with this LED from Marlin P Jones:
http://www.mpja.com/prodinfo.asp?number=12567+OP
Different LEDs have different voltage drops so you should check the voltage drop across the resistor and divide by the resistance to get the current. It should be no more than 20mA. With these LEDs, the current is 15mA, which is perfect.
Click to expand...

Ant time you want to edit/update that FAQ I just created, just PM me with the info and I'll add it.

Paul
 
Thanks Doc, can you post a picture of the relay to ground wire/s that should be removed? I have two units to do.

TIA
 
Whaleman said:
Thanks Doc, can you post a picture of the relay to ground wire/s that should be removed? I have two units to do.

TIA
Click to expand...

The unit is all back together, but if you look at the picture, on the board where I have an arrow and the note to remove the relay, there are 2 pads just to the right of the relay, those are for the jumper.
 
It is on the right side of the relay, you can't see it from this angle. Take another picture showing the right side of the relay, maybe tilt those components on the right away from the relay also, so it's easier to see.
 
bringing this back from Zombieville. Got a 9090 today. So far have checked all the fuses, pulled and checked all the outputs and regreased them and resoldered the regulated P.S. board.
As for the jumper for the RELAY. There is none. Looks to have never been installed. I'm talking about the spot between the green cap (C12) and R06 to the immediate left of the relay (Front Left Corner as you are facing the front of the unit.) Serial#826082168 (Aug.'76). Unit has NOT been powered up yet.
I'll start a new thread for it.

Larry
 
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