Hi everyone,
To put it bluntly, my lovely Sony TA-F770ES amp was working perfectly fine until I, after much deliberation and research, decided to re-cap it on account of its age.
It now doesn't work, I regret absolutely everything, and I would like some help if at all possible!
I started off with just the Main (A) board - the smaller preamp/driver board, and the phono stage board. They're the smaller boards stacked up on the right.
After doing both, no issues, I put them back in to test it before moving on.
It powered up, the lights lit up, the power light went green, then a couple of seconds later it went into protection.
"Bugger", I said. OK, maybe I mis-connected something or something is shorting that shouldn't be. I took it all back apart and meticulously checked and reassembled everything.
Same issue.
A while ago I bought an 870ES donor amp which was not working and in a poor cosmetic state - I wanted to harvest it for the unobtanium parts such as ICs/switches/pots.
So I swapped in the donor amp's amp and EQ boards (they are identical apart from a couple of slightly more highly-specced values here and there to account for the extra power of the amp).
Same issue.
Now, my memory is hazy of exactly how long I spent fiddling and checking all my connections and making sure nothing was visually wrong, but somewhere along the line, the front panel and volume LEDs stopped working.
I learned from this thread https://www.diyaudio.com/community/threads/sony-ta-f770es-tone-control-oscillating.351940/ and somewhere else that the volume knob LED and all the other LEDs are in series and for some reason are crucial to the front panel circuit working properly.
So I double-checked everything, all the connections, all the ground points, I even swapped in the donor (again, identical) front panel control logic board but again the same issue.
I really want to try and troubleshoot this but I'm not entirely sure where to go from here. It seems like it might be something to do with the front panel LEDs/connections but I'm not adept enough at reading circuit diagrams to fully comprehend it.
It can't be completely dead because:
1. The LEDs on the Main (A) board light up - one green one orange
2. The heatsink gets warm so the main transistors are doing their thing
3. Despite the LEDs not working, the buttons on the front still operate the motorised rotary input switch
4. The remote control still works and operates the volume
But there's no attempt to trigger the protection circuit anymore.
Thanks so much in advance for any insight.
To put it bluntly, my lovely Sony TA-F770ES amp was working perfectly fine until I, after much deliberation and research, decided to re-cap it on account of its age.
It now doesn't work, I regret absolutely everything, and I would like some help if at all possible!
I started off with just the Main (A) board - the smaller preamp/driver board, and the phono stage board. They're the smaller boards stacked up on the right.
After doing both, no issues, I put them back in to test it before moving on.
It powered up, the lights lit up, the power light went green, then a couple of seconds later it went into protection.
"Bugger", I said. OK, maybe I mis-connected something or something is shorting that shouldn't be. I took it all back apart and meticulously checked and reassembled everything.
Same issue.
A while ago I bought an 870ES donor amp which was not working and in a poor cosmetic state - I wanted to harvest it for the unobtanium parts such as ICs/switches/pots.
So I swapped in the donor amp's amp and EQ boards (they are identical apart from a couple of slightly more highly-specced values here and there to account for the extra power of the amp).
Same issue.
Now, my memory is hazy of exactly how long I spent fiddling and checking all my connections and making sure nothing was visually wrong, but somewhere along the line, the front panel and volume LEDs stopped working.
I learned from this thread https://www.diyaudio.com/community/threads/sony-ta-f770es-tone-control-oscillating.351940/ and somewhere else that the volume knob LED and all the other LEDs are in series and for some reason are crucial to the front panel circuit working properly.
So I double-checked everything, all the connections, all the ground points, I even swapped in the donor (again, identical) front panel control logic board but again the same issue.
I really want to try and troubleshoot this but I'm not entirely sure where to go from here. It seems like it might be something to do with the front panel LEDs/connections but I'm not adept enough at reading circuit diagrams to fully comprehend it.
It can't be completely dead because:
1. The LEDs on the Main (A) board light up - one green one orange
2. The heatsink gets warm so the main transistors are doing their thing
3. Despite the LEDs not working, the buttons on the front still operate the motorised rotary input switch
4. The remote control still works and operates the volume
But there's no attempt to trigger the protection circuit anymore.
Thanks so much in advance for any insight.
Did you take pictures of the boards before you started? You might have a cap in the wrong polarity. It could also not be entirely your fault since sometimes the silkscreen indications are not correct. So you should compare against the original if you can.
Protection mode is often one or both main amplifier boards or the power supply itself.
Check for incorrectly polarized capacitors that have recently been replace.
Man made faults are the worst.
Follow the schematic in the service manual. After checking the power supply, start at the output stage, working towards the input. You will soon find whare the issue is.
Check for incorrectly polarized capacitors that have recently been replace.
Man made faults are the worst.
Follow the schematic in the service manual. After checking the power supply, start at the output stage, working towards the input. You will soon find whare the issue is.
Why, in heaven's name did you get it into your head to replace capacitors in a well-functioning device?
I was once asked by a guitarist to replace all the capacitors in his amplifier with orange caps. I told him what it would cost but that I wouldn't do it. I also asked what he uses as the main effect apparatus.
"A Big Muff" he said.
All the more reason not to do it. Later, months later, he came back.
"You were right," he said, "I don't hear any difference with the Big Muff switched on. It was a waste of money."
There are many questions on the internet such as "What are the best capacitors, the best tubes, the best transistors, etc, etc."
Does the device sound good? Stay away from these "ideal component changes" and enjoy the music.
It's as simple as that.
But you're the boss.
I was once asked by a guitarist to replace all the capacitors in his amplifier with orange caps. I told him what it would cost but that I wouldn't do it. I also asked what he uses as the main effect apparatus.
"A Big Muff" he said.
All the more reason not to do it. Later, months later, he came back.
"You were right," he said, "I don't hear any difference with the Big Muff switched on. It was a waste of money."
There are many questions on the internet such as "What are the best capacitors, the best tubes, the best transistors, etc, etc."
Does the device sound good? Stay away from these "ideal component changes" and enjoy the music.
It's as simple as that.
But you're the boss.
Study this first. Always the first step certainly if one does not know jack of electronics. Reading starts with the same letter as "regret" 🙂
https://elektrotanya.com/sony_ta-f333esl_f770es_f870es_sm.pdf/download.html#dl
https://elektrotanya.com/sony_ta-f333esl_f770es_f870es_sm.pdf/download.html#dl
Best to divide and conquer when troubleshooting. Disconnect everything from the power supply. Does it work? Then attach one thing at a time. Do it until things don't work anymore.
Get a dim-bulb tester in there and see how it reacts when you power on.
Get a dim-bulb tester in there and see how it reacts when you power on.
Thanks for the suggestions and comments guys. I am going to have another look after work and see if I can shed any more light on it.
The caps are all good quality Nichicon/Panasonic from Farnell.
The caps are all good quality Nichicon/Panasonic from Farnell.
A few developments:
If I measure the voltage at the terminals on the input to the speaker connector board (before the relays) I get 17-20V DC. Half of the heatsink gets warm.
If I disconnect the Main A amp board (with the output midgets) and leave only the big central board, this voltage goes down to about 90mV. The heatsink stays pretty cool.
Voltages seem correct from what I can tell from the diagram.
In both cases the front panel does not light up and no relays operate. But the input selection still works.
Not really sure where to go from here 🙁
If I measure the voltage at the terminals on the input to the speaker connector board (before the relays) I get 17-20V DC. Half of the heatsink gets warm.
If I disconnect the Main A amp board (with the output midgets) and leave only the big central board, this voltage goes down to about 90mV. The heatsink stays pretty cool.
Voltages seem correct from what I can tell from the diagram.
In both cases the front panel does not light up and no relays operate. But the input selection still works.
Not really sure where to go from here 🙁
did you check to see if there was a short to ground on the output terminals? Check whether the output transistors are still good?
I have been working on an FA777ES- and the culprit is the selector switch- I found by pushing on the knob I could get the unit to work- though after a while it stops working-it is back with me to try and resolve the issue.
A mini breakthrough - I have restored the front panel LEDs by replacing transistor Q410 and the 1 ohm fusible resistor R653.
This brought it back to life and, with the Main A board disconnected, it comes out of protection.
But reconnecting this board put it back into protection. Disconnecting it and powering it up a moment later and it still stayed in protection.
Any thoughts of where to go other than testing all the transistors and resistors on the boards?
This brought it back to life and, with the Main A board disconnected, it comes out of protection.
But reconnecting this board put it back into protection. Disconnecting it and powering it up a moment later and it still stayed in protection.
Any thoughts of where to go other than testing all the transistors and resistors on the boards?
Service manual attached.
I assume you've confirmed all power supplies look nominal? As a general plan of attack, I suggest attempting the SM Section 4 adjustments of offset and bias current in each output amplifier. You will likely find a problem(s) in the process. Please describe any problems you encounter.
If these adjustments are successful but protection mode persists, the protection circuit itself may be the culprit. But let's defer that until you've got the PA circuits working.
Good luck!
I assume you've confirmed all power supplies look nominal? As a general plan of attack, I suggest attempting the SM Section 4 adjustments of offset and bias current in each output amplifier. You will likely find a problem(s) in the process. Please describe any problems you encounter.
If these adjustments are successful but protection mode persists, the protection circuit itself may be the culprit. But let's defer that until you've got the PA circuits working.
Good luck!
Thank you. Am I still going to be able to adjust these properly with the A board disconnected or the protection mode active?
This implies the transistor may have been damaged by too much current possibly caused by a reversed electrolytic capacitor. Before powering on make sure all electrolytics are connected properly and their polarity is respected. Do you have a schematic? It helps pin point what happened.
I believe both A and B boards have to be connected to have an intact PA. But protection mode should allow trouble shooting, I think.
I'm not discounting @edbarx comments. I suspect you've already exposed the amp to these perils. My suggestions maybe useful if you can't find obvious culprit.
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I’m certain the caps on the A board are all correctly oriented. And it still does it with the donor board. Although this maybe be because the bias on that board is very out of adjustment. It’s an odd one.
My instinct would be to use the original modules, guessing that donor boards have uncertain history. But another personal doctrine is to avoid removing/exchanging components--- I measure and analyze until I arrive at chief suspect. But I'm an old fart with old habits.