9090DB setting bias didn't go so well
- Thread starter Blue Shadow
- Start date
Blue Shadow
Waiting for Vintage Gear from this century
I've got grabbers, learned that lesson just blowing up a turntable not an amp. Only took out a single resistor. I was hoping to be able to do this with a voltage drop across the resistors. Maybe you can make it easier on my brain trying to figure out the voltage crop across the resistors. 30mA, 0.33Ω gives 10mV but some of the resistors supply one emitter and some supply two. I need to learn more to get that under control.
I've got to think some but here is the scat of the resistors on the end of the PS board on the bottom of the diagram and the transistors on the top. I'm going to look this over to learn it some more.
I've got to think some but here is the scat of the resistors on the end of the PS board on the bottom of the diagram and the transistors on the top. I'm going to look this over to learn it some more.
Hook your extra long grabber to one of the resistors on the end of the row, the easiest one to get to, and set it for about 3 millivolts. Discounting any other losses, that will give you 36 mA bias current for that channel. Repeat for the other channel. It won't hurt anything to have 36mA bias. If your really worried about it, set it a little lower.
.003/.33=.009A * 4 = .036A
The four emitter resistors, one per output transistor per channel, are in parallel on their way out to the zobel and then on to the relay, speaker switch, and then the terminals.
BTW, sorry for the delay, I couldn't read your schematic. I had to go find my paper SM.
.003/.33=.009A * 4 = .036A
The four emitter resistors, one per output transistor per channel, are in parallel on their way out to the zobel and then on to the relay, speaker switch, and then the terminals.
BTW, sorry for the delay, I couldn't read your schematic. I had to go find my paper SM.
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Blue Shadow
Waiting for Vintage Gear from this century
Yes, they make it hard to put all that on the one page and get it big enough. I tried and my pic here is fine.
I got the 30mA with meters I don't know about. I'm redoing this with the emitter resistor method and will get 3 millivolts and let that be the setting.
Right now I am uncomfortable with the tuner power supply. The caps removed, the large one next to the heat sink, C04, has a chunk of plastic hose on it and it is severely blackened. The other caps show some heat issues but C01, 100µ 35V in my unit was the one showing the most with a broken sleeve and a slightly bulging top.
Here are the numbers from the manual vs. what I have measured
Location, manual, measured
03 pin no voltage listed 52.2 measured
after R1&R2 14.0 --- 22.4
02 pin 5.8---7.5
01 pin 12.5---21.6
Base TR02 10.5 --- 22.5
These voltages are going to tire out the new caps (only one sees higher voltage than the cap is labeled) and the run the 270Ω resistors up to 240° and 270°F for the one in the open and the one next to the heat sink, respectively. I would think the unit would like a lower incoming voltage and I see Doug's response that the voltage needs to be up around 18-19 but at 22. it seems a bit high. Higher wattage resistors are on the list but maybe a bit more voltage drop would be good in this section. probably easier to handle the heat issues instead of redesigning the circuit for a voltage change.
Oh while typing this and finishing the bias verification, I have the unit driving speakers for the first time in many months. That is what happens when folks say no hurry.
I got the 30mA with meters I don't know about. I'm redoing this with the emitter resistor method and will get 3 millivolts and let that be the setting.
Right now I am uncomfortable with the tuner power supply. The caps removed, the large one next to the heat sink, C04, has a chunk of plastic hose on it and it is severely blackened. The other caps show some heat issues but C01, 100µ 35V in my unit was the one showing the most with a broken sleeve and a slightly bulging top.
Here are the numbers from the manual vs. what I have measured
Location, manual, measured
03 pin no voltage listed 52.2 measured
after R1&R2 14.0 --- 22.4
02 pin 5.8---7.5
01 pin 12.5---21.6
Base TR02 10.5 --- 22.5
These voltages are going to tire out the new caps (only one sees higher voltage than the cap is labeled) and the run the 270Ω resistors up to 240° and 270°F for the one in the open and the one next to the heat sink, respectively. I would think the unit would like a lower incoming voltage and I see Doug's response that the voltage needs to be up around 18-19 but at 22. it seems a bit high. Higher wattage resistors are on the list but maybe a bit more voltage drop would be good in this section. probably easier to handle the heat issues instead of redesigning the circuit for a voltage change.
Oh while typing this and finishing the bias verification, I have the unit driving speakers for the first time in many months. That is what happens when folks say no hurry.
If I'm reading correctly that you have 21.6V out of that board at pin 1 (connection C) then you're in danger of frying the tuner chip HA1196 which has a max supply voltage rating of 14V according to the data sheet I've seen. Other stuff won't like it either..
Blue Shadow
Waiting for Vintage Gear from this century
That is why I want to drop the voltage going into the tuner ps board. This could be done with a pair of 300Ω 7w resistors and leave about 19 Volts going in based on your numbers saying it should be about there. Maybe I should target a bit lower and could get 16.9V with a single 160Ω resistor. Of course, this one would be uprated to 15W and mounted off board. Since it is a ceramic not one of those cute little metal jobs, I'd probably mount it with a metal strap to the panel between the tuner and back half of the receiver to give it a little heat sink. Oh but I see that TR01 needs a 17 volt minimum to the collector off these/this resistor. So this means less 160Ω.
I'm sure 16.9V would work fine but the immediate problem is that the F2619 output is 21.6V.. Check your dolby calibration to see what I mean; the meter pointers will be way over to the right.
restorer-john
Addicted Member
Do you happen to know if Pomona still make the 4" long (5.5" overall length) long grabber? With the normal hook- not the maxi-grabber type end. I can't seem to find them.
Will trimmer on the tuner P/S board not adjust the voltage down? If not, you should disconnect power to the tuner until you get it sorted out. Check the zener, it should have 6 volts across it. Make sure the trimmer hasn't failed, then check your transistors.
The current model 5830 is a pincer style. Available from Digi-Key for $12 and change each. The maxigrabbers are hook style.
Blue Shadow
Waiting for Vintage Gear from this century
Meter switch to Dolby, Input to Aux, Dolby to Rec 1 and the left meter, nothing right meter to 75watts way right.
so you have a switch contact issue on the left channel. Turn off the tuner power supply...
Blue Shadow
Waiting for Vintage Gear from this century
I've got the unit off except for the measurements you have requested but I'll stop that now and try to figure out what you said about switch contact and turning off the tuner ps. No adjustment with the VR it appears. But I'll be looking over the scat for a few and try to see where that power goes and what switch it goes through so I can get that resolved.
Blue Shadow
Waiting for Vintage Gear from this century
I can't get a meaningful test of any of these four components on the board. I'll pull em tomorrow and see what they measure.
A scope really isn't useful in this case. I bought one of these a few years ago, and it has been super handy. However, I still test diodes and TO-92 transistors with my DMM.
In that circuit, look at the base-emitter drops on the three transistors. All should be around 0.6V. The zener should have about 6V across it. Make sure your probes are insulated, all but the last 1/16" of the tip. A piece of heatshrink or stripped wire insulation works fine.
A haven't seen a meter yet, cheap or expensive, that comes with decent probes for electronics work. These are excellent.
In that circuit, look at the base-emitter drops on the three transistors. All should be around 0.6V. The zener should have about 6V across it. Make sure your probes are insulated, all but the last 1/16" of the tip. A piece of heatshrink or stripped wire insulation works fine.
A haven't seen a meter yet, cheap or expensive, that comes with decent probes for electronics work. These are excellent.
Blue Shadow
Waiting for Vintage Gear from this century
Numbers don't look right with parts in situ. So I pulled the four components. Using the diode function, the zener measured correctly as did TR03.
TR01, 2SD313, didn't measure correctly.
+B>.549>C
+B>.549>E
+C>.001>E
+C>0L>B
+E>0L>B
+E>.001>C
TR0, 2SC1211, was off, too:
+B>.548>C
+B>.548>E
+C>.001>E
+C>0L>B
+E>.001>C
+E>0L>B
For D313 it seems that KSC2073 is preferred, but out of stock. Alternate is the TO-220 MJE-15032
For C1211 the search brings up the KSC2690AYS, a TO-220.
Are these the transistors I should use and should I throw a buck and a half in the kitty for different resistors to maybe drop the voltage a bit?
TR01, 2SD313, didn't measure correctly.
+B>.549>C
+B>.549>E
+C>.001>E
+C>0L>B
+E>0L>B
+E>.001>C
TR0, 2SC1211, was off, too:
+B>.548>C
+B>.548>E
+C>.001>E
+C>0L>B
+E>.001>C
+E>0L>B
For D313 it seems that KSC2073 is preferred, but out of stock. Alternate is the TO-220 MJE-15032
For C1211 the search brings up the KSC2690AYS, a TO-220.
Are these the transistors I should use and should I throw a buck and a half in the kitty for different resistors to maybe drop the voltage a bit?
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The C-E reading of .001 indicates a leaky transistor. MJE15032 is an excellent sub for 2SD313, better in every way.
2SC1364 is a TO-92. KSC1383 or KSC2310 would be a big upgrade.
What were you getting across the zener? Did you check the surrounding resistors, including the trimmer? Are any of the caps failed shorted?
2SC1364 is a TO-92. KSC1383 or KSC2310 would be a big upgrade.
What were you getting across the zener? Did you check the surrounding resistors, including the trimmer? Are any of the caps failed shorted?
