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X0X0DB Tuner Power Supply

CDFixer

CDFixer

Number 1 USC Trojan Fan
I have been wanting to do this for sometime but just never got around to it. We all know how hot this little power supply runs and that it is one of the failure points, I did a little experimenting and came up with the following modification.

Remove the 2 5W 270 ohm resistors.
Install a 200 ohm 25 Watt resistor in its place, use sleeving on the leads and place the resistor against the chassis.

This does two things, I moves the resistors away from the heat sink for the regulator transistor and by increasing the resistance by 65 ohms it reduces the voltage at the regulator from 34 to 21 volts the regulator does not have to work as hard as it did before and it doesn't get near as hot.

Here are the temps that I measured before and after the mod.

Starting temp before mod Heat sink 85F/29.4C Resistor Same
Temp 5 minutes after pwr Heat sink 153F/67.2C Resistor 164F/73.3C
Temp 10 Minutes after pwr Heat sink 166F/74.4C Resistor 168F/75.5C

Starting Temps After Mod Heat sink 91F/32.7C Resistor 81F/27.2C
Temp 5 minutes after pwr Heat sink 112F/44.4C Resistor 116F/46.6C
Temp 10 minutes after pwr heat sink 118F/47.7 Resistor 133F/56.1C
Temp 1 Hour after pwr up Heat sink 124F/51.1C Resistor 133F/56.1C

There is a radical difference in the temps before and after.

The regulator is adjustable so it will need to be adjusted to 12.5 volts after the mod.

I am fashioning a clamp for the resistor that will help disipate more heat to the chassis.
 

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Very cool Jim. Looks like an easy and effective mod. Are the original 5 W resistors in parallel?

- Pete
 
Yes the orginial resistors are in parallel so the resistance is effectivally 135 ohms. The voltages listed on the schematics are totally incorrect. They show an input voltage of about 44 volts when it is about 55 and it shows the voltage at the collector of the regulator as 14 volts, when it is closer to 34 volts. By doing the mod I reduced the heat output by about 40 degrees on each component. I am working on a clamp for the resistor that will hold it firmly to the chassis. I plan on using the two screws that hold down the tuner chassis for the clamp.
 
I haven't looked at the schematic, but as long as the regulator isn't current-starved under any condition that you can come up with, then looks fine to me.

...but I would have gotten a 25W aluminum resistor and mounted to the chassis somewhere.
 
Final results of the x0x0db tuner p/s mod?

CDFixer said:
Yes the orginial resistors are in parallel so the resistance is effectivally 135 ohms. The voltages listed on the schematics are totally incorrect. They show an input voltage of about 44 volts when it is about 55 and it shows the voltage at the collector of the regulator as 14 volts, when it is closer to 34 volts. By doing the mod I reduced the heat output by about 40 degrees on each component. I am working on a clamp for the resistor that will hold it firmly to the chassis. I plan on using the two screws that hold down the tuner chassis for the clamp.
Click to expand...

Has this modification been completed, and tested?
Any updated photos?

Thanks for all your help and advice on these units:thmbsp:

~dave
 
I have had a unit operating for several weeks with this modification and there are no problems.

I am going to on my next unit use an aluminum resistor mounted to the back of the tuner chassis. I will post some new pictures sometime next week.
 
CD Fixer, EW

I have a 9090db and have not looked for a hot tuner power supply board but I will and am looking of an aluminum 200 ohm 25 watt resistor to do this fix. I really appreciate this board and all the help you fellows provide.

Is it possible to do such a resistor change to fix the hot transistors on the Pioneer SX-1010 voltage regulator board?
Not knowing much about these circuits I just added the extra heat sink area and a cooling fan to just remove the excess heat. I like your solution here of changing the circuit even though there is still excess heat to get rid of (you move it away from the board).

Charlie
 
I found what appears to be a suitable resistor... Digikey part # RHRC-200-ND. (200 Ohm, 25W, Aluminum Housing)

Can someone please verify that this is an appropriate component?
 
Last edited:
I'm gonna do this to my 9090.

And Echo, if you read this :)

The 7 Sanken 2sc1116a's are going out tomorrow.
 
hpsenicka said:
I found what appears to be a suitable resistor... Digikey part # RHRC-200-ND. (200 Ohm, 25W, Aluminum Housing)

Can someone please verify that this is an appropriate component?
Click to expand...
That should work fine and look good to boot. You will have to find a place on the chassis to mount it and run wires back to the Tuner PS board. The advantage there is moving more of the heat away from that board.

- Pete
 
My tuner PS is A OK so I'm not gonna mess with it. Too much work for little gain. Of course, this doesn't mean thi sis the case for everyone else.
 
Donkey, the 9090and 8080 uses a completely different tuner power supply than the DB models. The power supply on the DB models also power the Dolby Board.
 
Will a single ceramic wirewound 220 ohm 10 watt resistor work? That is the closest I could find with my latest order. It looks just like the one used here.
 
I suspect it would work fine, but the aluminum one might be better at transferring heat to the chassis it is mounted on.

Mine was ordered from Digikey less than 2 weeks ago.... are they sold out?
 
I actually wanted to stay with ceramic which parts express had. It is in now and seems to work fine. IMHO having some airflow around the resistor packaging would seem to allow more heat to escape. Unless of course you paste the resistor to the case for heat transfer.

Now my question is the resistor running cooler becuase it is greater in watts or the fact that it is higher ohms than the 270 run in parallel equalling 135 ohms? I just don't have equipment, except my finger, to test before and after and both seem hot. The one before actually blackened the whole area around it.

I saw the Digikey part but I had to order some caps from PE.
 
For the first units that I did I used a 20 watt, resistor, since then I use a 25 watt aluminum resistor that I can mount on the chassis. The resistor is cooler due to the lower current through the resistor and the higher wattage. The transistor is cooler due to the reduce voltage drop across the regulator.
 
Can somebody who did this mod with the aluminum resistor explain (or post a pic) where they mount it? Also, should the wires going to the resistor be soldered to it, or can something like "quick disconnects" on the resistor leads be used instead?

Another question: do I understand correctly that the regulator which can be used to adjust the power supply after the mod is the one I circled on the pic taken from the original post describing the mod:

xoxo.jpg


Thanks.
 
I mount the resistor on the back splash of the tuner chassis. You just need to drill two holes and mount the resistor. Solder the resistor to the two outer holes on the power supply board. I would not recommend quick connects on the resistor.
 
One other thing - I assume the output from the power supply unit in on the bottom of the circuit, and hope I'll be able to figure out which is it. Thinking about it though, I'm not sure how physically to adjust it - with the tuner mounted (otherwise, I won't be able to connect it) - where should I read the target voltage (that 12.5 that I need)? Another thing is - after I've done the mod, should I just plug the receiver in and then adjust the voltage? Or should it be done differently? (Sorry for possibly stupid questions - I'm a newbie in this.)
 
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