they are 47uf electro's now,the plan was to replace with wima's which arent big,should go straight in no.
i have a friend who has these if i need them to try
vishay mkt .47uf 275v
wima mks2 .68uf 63v
wet tantalum 47uf 50v unknown make?
wima mks4 1.0uf 250v
evox mmk.47uf 16v
wima mkb polycarbonate .47uf 400v
tantalum bead 47uf 16v
what do think is a worth a try.
I wouldn't use tantalums at all although if one failed short circuit it would do no damage in that location, just reduce the bias and increase distortion. Tants are notoriously unreliable... avoid.
0.47 and 0.68 and 1uf are between 50 and 100 times to low in value compared to the original part 🙂
Personally I would use known good new electros but try things for yourself.
Any of those caps would not stop the amp working. Their function is to bypass the vbe mutiplier transistor at higher frequencies... and around 22 to 100 uf would be a typical value for many designs although some use much lower at around 0.1 uf.
0.47 and 0.68 and 1uf are between 50 and 100 times to low in value compared to the original part 🙂
Personally I would use known good new electros but try things for yourself.
Any of those caps would not stop the amp working. Their function is to bypass the vbe mutiplier transistor at higher frequencies... and around 22 to 100 uf would be a typical value for many designs although some use much lower at around 0.1 uf.
replaced the 47uf 10v's in the signal path ,with a pr of 100uf elna cerafine's,sound seems crisper..
turn on amp just now,now no sound through speakers🙁did smell a mild burning.also noticed when i turn the volume up and down ,that there is like a squeeking type of sound??? any ideas anyone..
What mods have you done since last time ?
Disconnect the speakers for their safety.
Identify what was burning.
Check for any solder bridges or splashes on the pcb.
Disconnect the speakers for their safety.
Identify what was burning.
Check for any solder bridges or splashes on the pcb.
since the 100uf elnas havent touch it,been injoying the music it makes mooly,will have alook in the morning,balls
i've had a look and to resistors have blown next to the attenuator,R211 and R261 both 1/4watt 68r's.
Something has happened for those resistors to fail...
There is no direct DC voltage or "path" that current can flow through available to them.
Apart from the attenuator they are also AC coupled and in series with 820 and 470 ohm resistors.
The only route I can see is if the attenuator were at low or zero ohms (in which case that may have suffered too) and current has flowed OUT of the opamp pins that connects to these resistors.
Both channels to fail the same way... the only common point is the PSU and grounds so I would check that the supplies are correct to the opamps and that the ground "lift" resistors R260 and R210 are intact. Check the DC voltage on all the opamp pins too.
There is no direct DC voltage or "path" that current can flow through available to them.
Apart from the attenuator they are also AC coupled and in series with 820 and 470 ohm resistors.
The only route I can see is if the attenuator were at low or zero ohms (in which case that may have suffered too) and current has flowed OUT of the opamp pins that connects to these resistors.
Both channels to fail the same way... the only common point is the PSU and grounds so I would check that the supplies are correct to the opamps and that the ground "lift" resistors R260 and R210 are intact. Check the DC voltage on all the opamp pins too.
Do not any mods and customizations without competent electrical knowledge! , i have this amp and he was calibrated, cleaned, measured with specialized electrical engineer . He wrote "..everything capacitor was fine capacitance without loss, only cleaned and conserved pots, corrected DC Offset mismatch to correct values" . I again advise dont replace caps with newer ones or premium types , is not logical, caps used in amp are best for this design , sony engineers arent idiots . Your activity can degrade an original design function/sound for this nice vintage amp.
each to own ravenman,😀 replaced resistors,checked all the above mooly,amp sounds awesome,thanks for your help mooly
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well turn on the amp this morning,the sound was awefull,wasnt sure what to check,have just checked the bias DC,was reading near 0mv,so adjusted to what the manual says, which is 7.5mv,managed or so thought to close this measurement.it measures anywhere from 7mv and upwards,very unstable,also tryed to play a track on cd,no sound at all??
Paul... this is going to need a methodical approach.
It would be a big help to have a scan of the power amp all on one picture (just the power amp), and just one channel to describe to you what to check.
I take it only one channel is faulty ?
Are we 100% sure it is a power amp fault ? Measuring on components that "may" have oxidised leads etc can result in what appear to be fluctuating readings. Sometimes best to bury the meter probes hard into the solder on the print side to get a guaranteed result.
Bias is variable (drifts with temperature) and but even with no bias the amp would still play and just sound a little "rough" at low volume.
It would be a big help to have a scan of the power amp all on one picture (just the power amp), and just one channel to describe to you what to check.
I take it only one channel is faulty ?
Are we 100% sure it is a power amp fault ? Measuring on components that "may" have oxidised leads etc can result in what appear to be fluctuating readings. Sometimes best to bury the meter probes hard into the solder on the print side to get a guaranteed result.
Bias is variable (drifts with temperature) and but even with no bias the amp would still play and just sound a little "rough" at low volume.
i get no sound out of either channel,when you say power amp,do you mean the main board
No sound out of either channel...
Check the basics first (and no speakers connected). The power amp is the part to the right of the opamps.
Measure all the supplies. So that means confirming the main - and + 48 volt rails to the power amps.
Measure the supplies to those opamps.
Confirm the DC voltage on the output of IC201 pin 1 is zero and that IC251 pin 7 is zero.
Also confirm that the DC output voltage of the power amps is zero. Measure on the main board itself as if there is an offset problem the relay will disconnect the speaker sockets.
It's to blurry to give you many reference numbers but measure the DC offset on the junction (which is the output) of what look like R377 and 378 and do the same for the other channel too.
Check the basics first (and no speakers connected). The power amp is the part to the right of the opamps.
Measure all the supplies. So that means confirming the main - and + 48 volt rails to the power amps.
Measure the supplies to those opamps.
Confirm the DC voltage on the output of IC201 pin 1 is zero and that IC251 pin 7 is zero.
Also confirm that the DC output voltage of the power amps is zero. Measure on the main board itself as if there is an offset problem the relay will disconnect the speaker sockets.
It's to blurry to give you many reference numbers but measure the DC offset on the junction (which is the output) of what look like R377 and 378 and do the same for the other channel too.
yes getting -48+48 volts
ic251 pin 7 reads 1.5v
ic201 pin 1 reads 1.2v
between r377 and r378 reads 2.2v
between r327 and r328 reads 1.1v
The 48 volts is OK
The reading on the opamps indicates a problem in that area. As this stage is AC coupled then the problem has to be local to that area. All these voltages are measured with respect to ground.
Confirm the supplies to the opamp are OK at -/+15 volts on pins 4 and 8 of the opamps.
In post 31 you mentioned R211 and 261 burning. Did you find a reason for that ?
The voltage from the junction of R377 and R378 to ground should be zero volts. If it is not then this indicates another separate issue in the power amp section.
The reading on the opamps indicates a problem in that area. As this stage is AC coupled then the problem has to be local to that area. All these voltages are measured with respect to ground.
Confirm the supplies to the opamp are OK at -/+15 volts on pins 4 and 8 of the opamps.
In post 31 you mentioned R211 and 261 burning. Did you find a reason for that ?
The voltage from the junction of R377 and R378 to ground should be zero volts. If it is not then this indicates another separate issue in the power amp section.
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