Fab, can I just lift one of the legs of D1 and D2 rather than remove them from the PCB board itself to test the steps? I will remove them completely only if either of them is mounted in wrong place.
Thanks
Thanks
With power OFF lifted D3 and D4 then I adjusted P1 to measure a resistance of 715 ohms between TP1-TP7 and also adjusted P2 to measure 785 ohms between TP2-TP8.
Then powered on by connecting both the grounds.
1. I did the step 8.8.5 and adjusted the current in input stage 2,5Vdc between TP8 and V-, 2,5Vdc between TP7 and V+.
2. Step 8.14 front end amplifier testing - P1 for about 0,3Vdc between TP6 and V- and I could dial it to 0.257Vdc. P2 for about 0,3Vdc between TP5 and V+ and I could dial it to 0.401Vdc with the offset being 0.2mV. So between positive and negative sides the difference is around 0.150Vdc and as long as I keep this difference the offset is <1mV.
3. After the above step I lifted the thermistors one after another away from the heat sink but the offset did not move a bit from 0.2mV.
Now looking at these values above are the thermistors an issue, as lifting both does not change the offset even a single mV.
Thanks
Then powered on by connecting both the grounds.
1. I did the step 8.8.5 and adjusted the current in input stage 2,5Vdc between TP8 and V-, 2,5Vdc between TP7 and V+.
2. Step 8.14 front end amplifier testing - P1 for about 0,3Vdc between TP6 and V- and I could dial it to 0.257Vdc. P2 for about 0,3Vdc between TP5 and V+ and I could dial it to 0.401Vdc with the offset being 0.2mV. So between positive and negative sides the difference is around 0.150Vdc and as long as I keep this difference the offset is <1mV.
3. After the above step I lifted the thermistors one after another away from the heat sink but the offset did not move a bit from 0.2mV.
Now looking at these values above are the thermistors an issue, as lifting both does not change the offset even a single mV.
Thanks
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Hi Manniraj
This does not make sense.
If you are able to have 2,5Vdc between TP8 and V-, 2,5Vdc between TP7 and V+ then you be able to get easily more than 0.3v at the mosfet driver source resistor. Measure mosfet driver Gaye resistance value and also source resistance value.
Power off amp and measure the maximum resistance you can get between TP1-TP7 and between Tp2-TP8 and report value. You may have a shorted thermistor(s). You can measure thermistor resistance without power.
Please post your board picture so I can see possible flaws like solder bridge or else.
Fab
This does not make sense.
If you are able to have 2,5Vdc between TP8 and V-, 2,5Vdc between TP7 and V+ then you be able to get easily more than 0.3v at the mosfet driver source resistor. Measure mosfet driver Gaye resistance value and also source resistance value.
Power off amp and measure the maximum resistance you can get between TP1-TP7 and between Tp2-TP8 and report value. You may have a shorted thermistor(s). You can measure thermistor resistance without power.
Please post your board picture so I can see possible flaws like solder bridge or else.
Fab
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Powering off and checking the maximum resistance using P1 for TP1-TP7 I get 3.2k and using P2 for TP2-TP8 I get around 5.42k.
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Hi manniraj
3.2k at room temperature is as expected. 5.42k is too high, probably your thermistor is open circuit or the pot P2 is damaged.
3.2k will be reduced by thermistor effect in parallel at higher temp to maybe 2,16k or so.
The 2.16k x 2.8ma (28mv/10 ohms)= 6v possible. 6v -2.4v (average vgs mosfet) = 3,6v margin >>> 0.3v.
Once you correct the thermistor or pot issue you must be able to check against voltage law:
V(tp1-tp7) = V(tp1-tp5) + V(tp5-tp7)
Thus
V(tp1-tp5) = V(tp1-tp7) - V(tp5-tp7)
If you are able to go higher than 2,5vdc for V(tp1-tp7) then you should have plenty of voltage for V(tp1-tp5)....
Verify the max voltage you are able to get at tp1-tp7 and tp2-tp8 (without targeting any dc offset value).
Is your V+ the same as tp1 and v- the same as tp2?
The manual does not require to get dc offset close to 0 when adjusting for 0.3vdc on both polarities...please do not adjust dc offset at this stage.
After all the above You can check with power off the integrity of q1 to q4 using the diode function of the multimeter and measuring Vbe and VCb of each transistor. NPN and PNP have reverse polarity.
Fab
3.2k at room temperature is as expected. 5.42k is too high, probably your thermistor is open circuit or the pot P2 is damaged.
3.2k will be reduced by thermistor effect in parallel at higher temp to maybe 2,16k or so.
The 2.16k x 2.8ma (28mv/10 ohms)= 6v possible. 6v -2.4v (average vgs mosfet) = 3,6v margin >>> 0.3v.
Once you correct the thermistor or pot issue you must be able to check against voltage law:
V(tp1-tp7) = V(tp1-tp5) + V(tp5-tp7)
Thus
V(tp1-tp5) = V(tp1-tp7) - V(tp5-tp7)
If you are able to go higher than 2,5vdc for V(tp1-tp7) then you should have plenty of voltage for V(tp1-tp5)....
Verify the max voltage you are able to get at tp1-tp7 and tp2-tp8 (without targeting any dc offset value).
Is your V+ the same as tp1 and v- the same as tp2?
The manual does not require to get dc offset close to 0 when adjusting for 0.3vdc on both polarities...please do not adjust dc offset at this stage.
After all the above You can check with power off the integrity of q1 to q4 using the diode function of the multimeter and measuring Vbe and VCb of each transistor. NPN and PNP have reverse polarity.
Fab
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I think you might be right as I can dial the maximum resistance of 3.2k on tp3-tp8 similar to tp1-tp7.
Sorry my mistake 🙁....this is tp3-tp8 then it means the thermistor and P2 are correct.😛
Thanks surfatwork!
Then if you set P1 and P2 correctly (no dc offset correction) you should get the 0.3v and more for tp1-tp5 and tp3-tp6.
Fab
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Hi Fab
I replaced the negative side thermistor and no change. Then I thought let me change the thermistor on the positive side as well. After I changed this thermistor and viola the voltages were close and I could set 0.300vdc on both the sides 🙂
The issue was with the thermistor on positive side. So now I replaced both the thermistors and by the way I saw someone actually used very thin heat shrink tubes on the legs of thermistors. So I also used the same and with a little heat could nicely make insulation on the thermistor legs 🙂
Bad news is that I damaged the D3/D4 diodes so I have to remove them from the board. Do not have any spares, so need to order it locally and I found this one 1N5240 - 10V Zener Diode - 500mW [1N5240] : Buy Online Electronic Components Shop, Price in India : electroncomponents.com
without any 'B' or 'C' mentioned and I presume this is fine to replace D3 and D4.
Thanks again.
I replaced the negative side thermistor and no change. Then I thought let me change the thermistor on the positive side as well. After I changed this thermistor and viola the voltages were close and I could set 0.300vdc on both the sides 🙂
The issue was with the thermistor on positive side. So now I replaced both the thermistors and by the way I saw someone actually used very thin heat shrink tubes on the legs of thermistors. So I also used the same and with a little heat could nicely make insulation on the thermistor legs 🙂
Bad news is that I damaged the D3/D4 diodes so I have to remove them from the board. Do not have any spares, so need to order it locally and I found this one 1N5240 - 10V Zener Diode - 500mW [1N5240] : Buy Online Electronic Components Shop, Price in India : electroncomponents.com
without any 'B' or 'C' mentioned and I presume this is fine to replace D3 and D4.
Thanks again.
Hi manniraj
Good to know that you were able to adjust for at least 0.3v. But you will need to get much higher than that once the output mosfet are installed to get more than 1A output bias. Can you try to increase the voltage at tp1-tp5 to at least 1.8v and the same for tp3-tp6 to ensure everything is right for sure. Afterwards you can reduce back to 0.3v to follow manual steps. In fact the 0.3v setting is only there at that step to ensure to start with a very low output bias once the lateral mosfet are installed, so only a precaution so that is why the exact value has no importance because the lateral mosfet will have a different VGS between the positive and negative side anyway.
For the thermistor leads sleeves should be installed by precaution as seen in the pictures of the manual..... but I think I removed the specific note at some point in one previous version of the manual....🙄
Sorry that you damage D3/D4🙁 the way I do it I use the tip of the soldering iron to reflow solder on one resistor lead/pad interface and at the same time with my other hand I lift off the lead using a long nose small plier. This way I do not damage anything.
Your selected diode should work fine since the tolerance is not critical at all.
Fab
Good to know that you were able to adjust for at least 0.3v. But you will need to get much higher than that once the output mosfet are installed to get more than 1A output bias. Can you try to increase the voltage at tp1-tp5 to at least 1.8v and the same for tp3-tp6 to ensure everything is right for sure. Afterwards you can reduce back to 0.3v to follow manual steps. In fact the 0.3v setting is only there at that step to ensure to start with a very low output bias once the lateral mosfet are installed, so only a precaution so that is why the exact value has no importance because the lateral mosfet will have a different VGS between the positive and negative side anyway.
For the thermistor leads sleeves should be installed by precaution as seen in the pictures of the manual..... but I think I removed the specific note at some point in one previous version of the manual....🙄
Sorry that you damage D3/D4🙁 the way I do it I use the tip of the soldering iron to reflow solder on one resistor lead/pad interface and at the same time with my other hand I lift off the lead using a long nose small plier. This way I do not damage anything.
Your selected diode should work fine since the tolerance is not critical at all.
Fab
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Yes Fab, I can dial the voltage more than 2v using P1/P2 across tp1-tp5 and tp3-tp6 respectively. I had to move the exact number of turns between these 2 trimmers to get the desired voltage. I could go all the way upto 3v on these trimmers. I have now dialled them back to 0.300vdc. So hopefully I should receive the diodes in couple of days and then I can move on to the next steps of mosfet installation and setup.
Thanks
Thanks