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Amplifier Repair - electrolytic capacitors expose metal top?
- Thread starter looxuser
- Start date
Hi 73's de Edd, Ok having read your instructions (Which i will repeat to the letter) simply for my learning can I clarity some points in bold below please (itallics) against your original text thus.....
have pins 3-4 and 5 of the CD4015 / IC604 totally floating.
We now just have to see if the 4051's will respond and do their switching changes when being manually addressed.
Work with one channels 4051 at a time and its connections .
Q. So, as there is going to be no signal (as 3,4,5 are now floating on the 4015) won't pins 9,10 & 11 of 4051's be at ZERO volts (LO) anyway therefore giving the LO LO LO address code? Curious why the 100ohms resistors pins 9.10,11 to ground (VSS pin 8) are needed? Not challenging your superior knowledge here just curious.
Whilst I go away and act on your kind recommendations here, can I ask you some other questions please, this time these relate to general electronics understanding:-
1. Above IC602 on the schematic (and below on the block diagram shown) the signal lines from IC604 are connected to a zener D952, a resister and a resistance transistor Q952 & Q953,954. Do you know what these do and if so could you explain the principle to me please, i'm trying to understand how those switching signals are used in these components? It seems strange to me that those signal lines are used and just don't run cleanly to the 4051's Shown here...
2. To the left of IC604, the Serial feeds to it go through zener diodes (1SS133 type commonly seen on this pcb) what is their function electronically?
3. Am i right in saying C607 is for decoupling?
Finally, if that not already enough taxing questions my final one is in terms of IC's in general, can defective components external to the IC typically effect the operation of the IC itself?
Kind Regards, Andy
have pins 3-4 and 5 of the CD4015 / IC604 totally floating.
We now just have to see if the 4051's will respond and do their switching changes when being manually addressed.
Work with one channels 4051 at a time and its connections .
Q. So, as there is going to be no signal (as 3,4,5 are now floating on the 4015) won't pins 9,10 & 11 of 4051's be at ZERO volts (LO) anyway therefore giving the LO LO LO address code? Curious why the 100ohms resistors pins 9.10,11 to ground (VSS pin 8) are needed? Not challenging your superior knowledge here just curious.
Whilst I go away and act on your kind recommendations here, can I ask you some other questions please, this time these relate to general electronics understanding:-
1. Above IC602 on the schematic (and below on the block diagram shown) the signal lines from IC604 are connected to a zener D952, a resister and a resistance transistor Q952 & Q953,954. Do you know what these do and if so could you explain the principle to me please, i'm trying to understand how those switching signals are used in these components? It seems strange to me that those signal lines are used and just don't run cleanly to the 4051's Shown here...
2. To the left of IC604, the Serial feeds to it go through zener diodes (1SS133 type commonly seen on this pcb) what is their function electronically?
3. Am i right in saying C607 is for decoupling?
Finally, if that not already enough taxing questions my final one is in terms of IC's in general, can defective components external to the IC typically effect the operation of the IC itself?
Kind Regards, Andy
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Electrolytics do not suffer idleness well. They can cause big trouble when idle for long periods, needing periodic charging to stay "formed" and maintain the oxide layer that insulates the conducting plates. Sometimes they can be "reformed" by a slowly rising return to working voltage. Even with regular use, electrolytics fail with age by drying out or leaking electrolyte following internal corrosion. If the electrolytic bulges, shows obvious loss of electrolyte, or simply can't be reformed you must replace it.
Hi 73's de Edd, so I've done that testing you suggested with I the following results...
a. So with a LO LO LO (TAPE) address code into IC602 and inject via isolation cap I get audio at reasonable volume on all front panel source switch positions except Video 2 which is at least twice as loud.
b. So with a LO LO HI (TUNER) I get audio WITHOUT any injection via isolation cap. This is to be expected though as thats the audio source we lifted off pin 14 right?
c. So with a LO HI LO I get same result as (a) above.
d. So with a LO HI HI I get same result as (a) above.
More observations for you...
- The source position/selection on front panel makes no difference to whether signal is stronger. In all cases when you select "video 2" its much stronger though to the extent you have to turn down the volume.
- When the injected signal is removed, there is a very feint sound being produced which is feint indeed and it can be muted with the front mute button.
- Only on injecting that isolation cap source to the expected source pin on IC602 do you get audio i.e we select TAPE LO LO LO if you inject at any other pin you dont get audio which is a good sign.
- When injecting the audio to one of the IC's 601 or 602, like you say that's addressing both IC's so it was strange to me to find only one speaker sounded. I tried the injection on the same pin of IC601 & 602 and was able to switch the sound output either left or right. Neither were both on at the same time.
Finally I tested IC604 (that 4015) with pins 3,4 ,5 now floating of course and its giving HI (8.5v) on pin 3 and LO on pins 4 & 5 regardless of front panel selector position.
Welcome your further comments on my results here, Kind Regards, Andy
a. So with a LO LO LO (TAPE) address code into IC602 and inject via isolation cap I get audio at reasonable volume on all front panel source switch positions except Video 2 which is at least twice as loud.
b. So with a LO LO HI (TUNER) I get audio WITHOUT any injection via isolation cap. This is to be expected though as thats the audio source we lifted off pin 14 right?
c. So with a LO HI LO I get same result as (a) above.
d. So with a LO HI HI I get same result as (a) above.
More observations for you...
- The source position/selection on front panel makes no difference to whether signal is stronger. In all cases when you select "video 2" its much stronger though to the extent you have to turn down the volume.
- When the injected signal is removed, there is a very feint sound being produced which is feint indeed and it can be muted with the front mute button.
- Only on injecting that isolation cap source to the expected source pin on IC602 do you get audio i.e we select TAPE LO LO LO if you inject at any other pin you dont get audio which is a good sign.
- When injecting the audio to one of the IC's 601 or 602, like you say that's addressing both IC's so it was strange to me to find only one speaker sounded. I tried the injection on the same pin of IC601 & 602 and was able to switch the sound output either left or right. Neither were both on at the same time.
Finally I tested IC604 (that 4015) with pins 3,4 ,5 now floating of course and its giving HI (8.5v) on pin 3 and LO on pins 4 & 5 regardless of front panel selector position.
Welcome your further comments on my results here, Kind Regards, Andy
HI 73's de Edd, I've soldered in a DIP16 socket for that IC 4015B and went ahead and ordered a replacement IC for just afew Pence only. So I will give that a try whilst I wait to hear from you regarding IC 604 evaluation for address corruption, given the serial digital stream addresses your display properly responding to inputs. Who knows it may only be that IC defective and it fixes the issue but I doubt it purely because of the fact that the volume is louder when Video 2 is selected. Oh hang on though, thinking about this a little further this behaviour now its not unexpected. We have off course now got IC604 floating on the instruction side to IC601 & 602, but we don't have the attenuation sides of that 4015IC floating also. So when we press the front source select buttons:-
1. The buttons action is sensed by the front PCB controller IC which changes the display.
2. The controller IC should then be sending signals to IC604 to change its binary output config to suit the source selected. because these are floating that has no effect of course you can cycle through them but...
3. Because pins 2, 11,12,13 of IC 604 are not floating, when cycling through them, attenuation changes when Video 2 is selected, i.e louder than the rest.
I'm learning alot here, but no quite there on why the IC604 isn't changing its binary output.
Oh one other observation, I posted on March 4th a query re the components in parallel to the serial connection between the IC's in question here. It has now dawned on me that these are for providing instructions to the optional Digital Audio Tape machine. Because I don't have that I may just remove these components to see if they have interfered with the signals to IC601 & 602
1. The buttons action is sensed by the front PCB controller IC which changes the display.
2. The controller IC should then be sending signals to IC604 to change its binary output config to suit the source selected. because these are floating that has no effect of course you can cycle through them but...
3. Because pins 2, 11,12,13 of IC 604 are not floating, when cycling through them, attenuation changes when Video 2 is selected, i.e louder than the rest.
I'm learning alot here, but no quite there on why the IC604 isn't changing its binary output.
Oh one other observation, I posted on March 4th a query re the components in parallel to the serial connection between the IC's in question here. It has now dawned on me that these are for providing instructions to the optional Digital Audio Tape machine. Because I don't have that I may just remove these components to see if they have interfered with the signals to IC601 & 602
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Hello all, especially 73's de Edd, WOW SUCCESS my old amp is now working perfectly!!! I'm delighted to have found that it turned out to be a duff IC which I would never have expected if if wasn't for 73's de Edd instructions and indeed teachings. Yes delighted and my appetite is now watered for more fixes. So a BIG BIG thanks from me to 73's de Edd for all your help. Please join me in saying thanks to 73's de Edd for the contribution to this Forum and all the time he spends helping people out.
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