|Solid State Talk all about solid state amplification.|
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|16th March 2019, 08:29 AM||#111|
Working through the posts...
The only result that mattered was the behaviour of the amp with pin 7 grounded. It seems like doing this did indeed change the behaviour (which is good) but what we really needed was the voltage check of offset.
You could do that by anticipating that the click was the speaker relay connecting correctly and so wiring the meter across the speaker sockets and seeing what happened.
This result is a big step forward though and hopefully shows the main amp is basically OK. The circuit also seems to show a single LED, not a bi-colour type.
Discharging caps. Normally the circuit itself will do that. Just check to make sure there is no high voltage across them. Anything under a couple of volts is OK to begin working on the amp. To manually discharge a large cap use a resistor appropriate to the voltage. A 4k7 2watt carbon type should cover most situations on solid state stuff.
The shiny green is a mask which we call solder resist. The board still looks like a phenolic resin type to me and will have a distinct smell as you solder on it. The discolouration in response to long term heat is perfectly normal though.
The soldering looks pretty much par for the course tbh. Look at the last pictures in post #1 here which show the kind of thing to be aware of. Some of those joints on your board look very suspect but I would beware at this stage of doing more remedial work... try and diagnose and fix the issue at hand first.
Sony CDP790 and KSS240 Restoration Project
The cap marked 471 is a 470pF polystyrene type. Its 4 and 7 and then 1 zero as the multiplier. 473 would be 47,000pF or 47nF (nano) or 0.047uF.
So where next
Well I guess you have to replace that opamp and also clean the top area of the board around the opamp gently. The voltage you measured on pin 7 earlier is the one thing I have doubts over... because I would have expected it to be stuck more toward the supply rail than an indeterminate voltage.
That doesn't change anything as far as we are concerned, its just a case of,
1/ Is the opamp alone genuinely faulty? It would still be last on my list of suspects tbh.
2/ Is the problem contamination on the top of the board affecting the high impedance circuity of the opamp? This means replacing the opamp may well fix the issue as contamination is automatically burned off and removed.
3/ Is the problem one of the passive parts around the opamp. It happens, however unlikely.
Installing and using LTspice IV. From beginner to advanced.
|16th March 2019, 12:37 PM||#112|
Sorry I cannot be more helpful.
|16th March 2019, 08:57 PM||#113|
Join Date: Jul 2013
Seems like SOLID RED LED = "PLAY"...
Thanks DRUIDAUDIO. No drama.
By all accounts, it seems like a solid red LED = "PLAY".
I have several different amps, so I can't quite recall either.
Let's just see how it plays out...
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