Hi Bigred,
You should see the Sony fakes, under the real Sony # and at the real Sony $$$$. No shame.
The $50 minimum isn't as bad as it seems. You aren't going to buy $5 worth and order from BC are you? The bill adds up depressingly quickly when you order parts.
Electrosonic had a $25 min. order. I didn't have any trouble clearing that.
-Chris
You should see the Sony fakes, under the real Sony # and at the real Sony $$$$. No shame.
The $50 minimum isn't as bad as it seems. You aren't going to buy $5 worth and order from BC are you? The bill adds up depressingly quickly when you order parts.
Electrosonic had a $25 min. order. I didn't have any trouble clearing that.
-Chris
Well this whole Global thing has got me depressed and also very 
Yeah the bills add up VERY quickly especially at GLOBALs markup 
I can see why Jerry is making a good living!! $72 for outputs as compared to $16 even with shipping and US exchange is a steal... I think I know where I'll be gettin my semiconductors now.
Yeah the bills add up VERY quickly especially at GLOBALs markup I can see why Jerry is making a good living!! $72 for outputs as compared to $16 even with shipping and US exchange is a steal... I think I know where I'll be gettin my semiconductors now.
Hi Ricardo,
Replace the amp or use the old PCBs as a guide to make new ones. I have done this in the past for simpler boards. It's less expensive to buy another amp off Ebay that might need some work. The PCB is the amp.
The only other possibility is that a member has made a new amp in a Denon chassis (not likely).
-Chris
Replace the amp or use the old PCBs as a guide to make new ones. I have done this in the past for simpler boards. It's less expensive to buy another amp off Ebay that might need some work. The PCB is the amp.
The only other possibility is that a member has made a new amp in a Denon chassis (not likely).
-Chris
Hi
I am rebuilding the POA6600A board .... again..
As I am afraid to burn the trannies again, I am experimenting the voltages without any output transistors.
Now I get the following measures:
1.55v (too low) on TR509 base (pre driver positive)
-1.69v (normal spec) on TR510 base (pre driver negative)
running back in the pcb I read :
-1.82v on TR551 emitter (should be -1.7v)
1.67v on TR551 collector (should be 1.75v)
I believe the problem is here but do not know how to raise the collector value and reduce the emitter.
Really would apreciate some expert gidance as I am new to these matters.
Best Regards
Ricardo
I am rebuilding the POA6600A board .... again..
As I am afraid to burn the trannies again, I am experimenting the voltages without any output transistors.
Now I get the following measures:
1.55v (too low) on TR509 base (pre driver positive)
-1.69v (normal spec) on TR510 base (pre driver negative)
running back in the pcb I read :
-1.82v on TR551 emitter (should be -1.7v)
1.67v on TR551 collector (should be 1.75v)
I believe the problem is here but do not know how to raise the collector value and reduce the emitter.
Really would apreciate some expert gidance as I am new to these matters.
Best Regards
Ricardo
Hi Ricardo,
Stop. Use diodes to simulate the emitter - base junctions on the output transistors you pulled. Your readings might make more sense then.
-Chris
Stop. Use diodes to simulate the emitter - base junctions on the output transistors you pulled. Your readings might make more sense then.
Huh? What did you read and how are you testing those. Look up the data sheet on them. These are "digital transistors". Most have a resistor in series with the base and possibly one from base to emitter (behind the first base resistor).
-Chris
anatech said:
Hi Chris
I have two amps so I can compare readings:
Before the recently installed trannies blew I measured the following differences on TR601:
Bad Amp B 15.2mv C 137.4mv E 0v
Good Amp B 0.5mv C 13.9mv E 0v
That is why I believe TR601 is faulty.
Another question...:
Can the optocoupler be dead ? (When the output trannies blew, I measured -80v on pin 3 of IC501... so it can be affected)
I bought some new ones but they seem to have different specs:
The original is TLP521-1 (BL)
I have got the replacements:
TLP521-1(A,F,T)
TLP521-1(Y)
TLP521-1(GB)
Can I use any of those ? (The difference between them and the original part seems to be related only with the precision of the Current Transfer Ratio (%):
Original - Min 200% Max 600%
TLP521-1(GB) - Min 100% Max 600%
I believe the problem is related with the bias circuit but can not identify the reason.
Can you please send me a schematic with comments regarding the several sections ?
On C531 I read -1.8v
TR510 base = -1.69
On C530 I get 1.67v
TR509 base = 1.55v
Why are these values not simmetrical ?
And the grey whire should be 0v and I always have -.07v...why??
When i adjust VR501 I can modify the voltages in R553 and R554 at the same time, so the raltive difference is not altered.
When I adjust VR502 the only difference is on pin 4 of IC501 that can vary in only .05v.
Is this normal ?
Best Regards
Ricardo
Hi Ricardo,
All right now. Let's proceed in a rational manner from here on in.
When you take measurements in an output stage, it's often more intelligent to take them with respect to the speaker output terminal (unless it's a capacitor coupled output). That way you get more accurate readings and you can see what the base - emitter drops are.
Also, 0 V on a schematic is often wrong or an idealized case. I only trust that a point is a DC average of 0 V when it is a ground point. So your output voltage should be exactly 0 VDC in a perfect world. Realistically you will read anywhere less than |100 mV| (absolute value). Often this voltage may be less than |10 mV|, but never perfectly zero. I guess that might depend on the resolution of your instrument too.
Bias currents are normally given in mV, but on a schematic may be written as 0 V. Notice it wasn't written as 0.000 VDC.
So, have another look and pay attention to the base - emitter voltage drops. Your DC offset is important if it measures over, say for argument, 50 mV. You are more interested in offsets on the order of volts or above.
-Chris
-Chris
All right now. Let's proceed in a rational manner from here on in.
When you take measurements in an output stage, it's often more intelligent to take them with respect to the speaker output terminal (unless it's a capacitor coupled output). That way you get more accurate readings and you can see what the base - emitter drops are.
Also, 0 V on a schematic is often wrong or an idealized case. I only trust that a point is a DC average of 0 V when it is a ground point. So your output voltage should be exactly 0 VDC in a perfect world. Realistically you will read anywhere less than |100 mV| (absolute value). Often this voltage may be less than |10 mV|, but never perfectly zero. I guess that might depend on the resolution of your instrument too.
Bias currents are normally given in mV, but on a schematic may be written as 0 V. Notice it wasn't written as 0.000 VDC.
So, have another look and pay attention to the base - emitter voltage drops. Your DC offset is important if it measures over, say for argument, 50 mV. You are more interested in offsets on the order of volts or above.
-Chris
-Chris
Thank you Chrisanatech said:
I am measuring values without the output trannies in place because every time I solder them in place, they blow after a while so I can not get a reading of DC offset in the output sockets.
I believe I should be able to set the voltage differential between the bases of the pre drivers so as the readings should be simmetrical relative to ground.
Can you explain how to measure base emmiter voltage drop ?
Regards
Ricardo
Hi Ricardo,
To measure the voltage drop across the emitter and base of a transistor, you put the leads in those positions. I like to use positions further away so as not to slip and blow components up.
-Chris
You can do this without blowing outputs. One way is to use a variac to power up the amplifier, the other is to use an external, variable power supply. Some people have been successful in using light bulbs in series with the unit to limit the energy. I haven't, so I can't comment.
Okay, you try that. My way is accurate and much, much easier. Never mind faster and correct.
To measure the voltage drop across the emitter and base of a transistor, you put the leads in those positions. I like to use positions further away so as not to slip and blow components up.
-Chris
Hi Chris
Hope you can guide me in the POA6600A layout....
After replacing all el caps (except the bipolars) I switched on without output trannies and everything looked fine for 30 min or so.
Then, the readings started to change and now I get positive values on both drivers emmitters.
They should be +0.5v on TR511 and -0.5v on TR512.
Also, R521 and R522 read 5.1ohm instead of 4r7 as stock.
The voltage on TR505 collector is now 2.4v instead of 1.75.
can be due to TR505 fault ?
Regards
Ricardo
Hope you can guide me in the POA6600A layout....
After replacing all el caps (except the bipolars) I switched on without output trannies and everything looked fine for 30 min or so.
Then, the readings started to change and now I get positive values on both drivers emmitters.
They should be +0.5v on TR511 and -0.5v on TR512.
Also, R521 and R522 read 5.1ohm instead of 4r7 as stock.
The voltage on TR505 collector is now 2.4v instead of 1.75.
can be due to TR505 fault ?
Regards
Ricardo
Hi Chrisanatech said:
Following your instructions I read the base emitter voltage drop in all transistors and the values are all between 0.55 and 0.6 v
I believe they are ok.
Measuring RN1205 in the bias circuit, I do not get this voltage drop (Base Emmiter) maybe because I have no signal running ??
After some resoldering I believe I solved the oscilations problem and the unit is now stable.
Nevertheless, I still can not make the pre drivers / drivers output values to be simetrical relative to ground.
In the NPN driver emitter I read 0.33v (too low) and on PNP driver emitter I read -0.5v (This one is correct).
Can I solder some output trannies even if I have this differences ?
Your comment will be of the utmost importance to me.
Best regards
Ricardo
Way to go!
Hi Ricardo,
Sorry, I've been off and on lately. I have things going on personally that prevent me from giving you my full attention.
-Chris
Hi Ricardo,
Sorry, I've been off and on lately. I have things going on personally that prevent me from giving you my full attention.
Yes, they are. Easier doing it this way? The readings are more stable aren't they?
Yes, no E-B voltage means the transistor is not turned on (or it has a B-E short). It's possible to have up to 0.4 VDC on a standard transistor with out current flow from E-C.
That's very good news. Good going.
They never are completely. Often, this type of problem will be found in the voltage amplifier stages.
It sounds like you have extremely low to no bias current at all.
Yes. If anything you will not have enough current flow in the output transistors. The oscillations you had may have been the problem. Do check the low value resistors (below 1 K ohm) even if they look fine before installing your outputs.
You seem to be doing really well on your own to be honest with you.
-Chris
Hi Chris
I installed only two output trannies and the amp is working.
I am hearing it trough a woffer speaker without enclosure and using a walkman in the input so I can not tell if the sound is good.
I do not seem to notice any distortion.
I have not been able to make the output trannies bases voltages simmetrical... (+0.47 NPN -0.67 PNP).
I read 70mv in the speaker terminals.
I have readings between 1 and 7mv on points TP (34) when music is playing.
Can I assume the unit will not distort and solder some more trannies ?
Thank you for time and help.
Regards
Ricardo
I installed only two output trannies and the amp is working.
I am hearing it trough a woffer speaker without enclosure and using a walkman in the input so I can not tell if the sound is good.
I do not seem to notice any distortion.
I have not been able to make the output trannies bases voltages simmetrical... (+0.47 NPN -0.67 PNP).
I read 70mv in the speaker terminals.
I have readings between 1 and 7mv on points TP (34) when music is playing.
Can I assume the unit will not distort and solder some more trannies ?
Thank you for time and help.
Regards
Ricardo
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