I bought a '93 SONY F808ES 120 wpc integrated amp that needs repair. It is built like a tank and weighs in at 53 lbs. There is a sticker indicating it was a refurbished unit when originally purchased. I bought it very cheap, for repairing because it is supposed to be one of Sony's best integrated w/ their best phono stage. Sorry I don't have interior photos, but there's plenty on the web.
It doesn't output any dc at the speaker terminals, which is a good thing.I cleaned all the pots and switches w/ deoxit and adjusted dc bias. This is the limit of my testing skill.
The sound is anemic with no body or bass, and plays only quietly with no drive or volume. When operating stereo/mono switch the sound becomes barely audible in mono while buzzing in the speakers. After playing in stereo mode for about 5 minutes the sound gets very quiet and overrun with hum in the speakers, which is louder than the music playing. A visual inspection of the inside shows nothing burned, bloated, or out of the ordinary, but it obviously has some issues.
There is no power amp input to test the power amp alone, but there is a preamp out. I tried the preamp output and the same issues exist with another power amp, so I'm guessing it is isolated to the preamp. I'm not tech, but I will pull the main preamp board and examine it more closely, especially concerning the components related to the mono/stereo switch. Can I check capacitors, diodes, and resistors while in place on the circuit board?
A little basic advice on testing the components would be appreciated. Here is the SM.
Sony TA-F808ES | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
It doesn't output any dc at the speaker terminals, which is a good thing.I cleaned all the pots and switches w/ deoxit and adjusted dc bias. This is the limit of my testing skill.
The sound is anemic with no body or bass, and plays only quietly with no drive or volume. When operating stereo/mono switch the sound becomes barely audible in mono while buzzing in the speakers. After playing in stereo mode for about 5 minutes the sound gets very quiet and overrun with hum in the speakers, which is louder than the music playing. A visual inspection of the inside shows nothing burned, bloated, or out of the ordinary, but it obviously has some issues.
There is no power amp input to test the power amp alone, but there is a preamp out. I tried the preamp output and the same issues exist with another power amp, so I'm guessing it is isolated to the preamp. I'm not tech, but I will pull the main preamp board and examine it more closely, especially concerning the components related to the mono/stereo switch. Can I check capacitors, diodes, and resistors while in place on the circuit board?
A little basic advice on testing the components would be appreciated. Here is the SM.
Sony TA-F808ES | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
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Before diving in deep I would first check more basic things... it sounds a strange fault (both channels affected... hum etc) to be a genuine component failure, or at least I wouldn't immediately assume that.
Check for damage and breaks in the PCB (hairline cracks due to impact damage) around any "sticky out bits" such as pots and switches. It should be fairly easy to see where its all going wrong with a scope and simply tracing a line level signal end to end.
Check for damage and breaks in the PCB (hairline cracks due to impact damage) around any "sticky out bits" such as pots and switches. It should be fairly easy to see where its all going wrong with a scope and simply tracing a line level signal end to end.
I removed and studied the control and tone circuit boards mounted on the front panel, and they look fine. I also see why it was a refurbished unit. There are some circuit traces on the control board that were bad and they were touched up w/ solder. I really studied this board and every thing seems fine.
I also cleaned the cheap stereo/mono and rumble filter w/ deoxit. They are spring loaded push button switched and now they don't come out w/o pulling on them, like there is no lubrication in them anymore.
I will dig deeper and look at the input circuit board tomorrow.
I also cleaned the cheap stereo/mono and rumble filter w/ deoxit. They are spring loaded push button switched and now they don't come out w/o pulling on them, like there is no lubrication in them anymore.
I will dig deeper and look at the input circuit board tomorrow.
I would suspect two things - one is an intermittent ground line somewhere, and the other would be elecrolytic caps. Not the main ones, but ancillary ones in the PSU filter stages of the main amp, AND - very important, any audio electrolytic caps in various places. This amp may still have the Elna Duorex audio caps, which are prone to 'sudden death' failure and leakage, with various strange effects.
The service manual for this amp should be available on the web for free. Note that in some versions of the manual the bias setting procedure had an error (assumed measuring a voltage drop across one vs two source resistors of the output transistors) which ended up in a very high bias, and lots of heat, as well as somewhat dead sound (but nothing like your problem). Properly adjusted, it's one of the best integrated amps I know of, and believe me I've listened to plenty (never mind being under the hood of them too
).
The general setup of the amp is a high-gain power amp with passive front end and a separate phono pre. Not sure off-hand if it has a 'direct' input (it's predecessors did), this provides a signal directly to the volume pot, omitting every other input switching component, and the volume pot is directly at the input of the main amplifier. Testing it through that may offer more clues. Also, try out both speaker outputs, we might be dealing with two problems.
The service manual for this amp should be available on the web for free. Note that in some versions of the manual the bias setting procedure had an error (assumed measuring a voltage drop across one vs two source resistors of the output transistors) which ended up in a very high bias, and lots of heat, as well as somewhat dead sound (but nothing like your problem). Properly adjusted, it's one of the best integrated amps I know of, and believe me I've listened to plenty (never mind being under the hood of them too
).The general setup of the amp is a high-gain power amp with passive front end and a separate phono pre. Not sure off-hand if it has a 'direct' input (it's predecessors did), this provides a signal directly to the volume pot, omitting every other input switching component, and the volume pot is directly at the input of the main amplifier. Testing it through that may offer more clues. Also, try out both speaker outputs, we might be dealing with two problems.
I notice the hum is persistent all the time and gets louder as the volume is turned up. The music sometime conceals it but its alway there as you can tell on an input w/o any source connected.
I see two pairs of large caps. Which should I check?
Here is a photo of inside from the web.
I have the manual from hifiengine, but not much of a tech.
I see two pairs of large caps. Which should I check?
Here is a photo of inside from the web.
I have the manual from hifiengine, but not much of a tech.
Attachments
Ok, I tested the smaller pair of the electrolytic caps with my Fluke 179 meter and they test 8200uf as stated. I tried testing the larger 15,000uf caps in the center of the amp, but my meters auto range only goes to 10,000uf and it reads out of range. How can I test them and/or how can I test for leakage?
The correct tool to do this is an ESR meter. Another way is to use an oscilloscope and check for excessive ripple on the supply lines.
However you can safely assume with the age of the amplifier, that the capacitors require renewal. Basically, if it's an electrolytic capacitor, replace it. Renew all of the small ones first, then check.
Also, have you tried Source Direct turned on ? The preamp in this amp is actually passive, except for the tone controls, and the phono preamp. For line inputs, with Source Direct on, the signal is routed straight to the power amp via the volume pot.
However you can safely assume with the age of the amplifier, that the capacitors require renewal. Basically, if it's an electrolytic capacitor, replace it. Renew all of the small ones first, then check.
Also, have you tried Source Direct turned on ? The preamp in this amp is actually passive, except for the tone controls, and the phono preamp. For line inputs, with Source Direct on, the signal is routed straight to the power amp via the volume pot.
You create two thread with same problem I see
http://www.diyaudio.com/forums/solid-state/238444-testing-locating-filter-capacitor.html
Show us what is AC voltage from the transformer & DC voltage on the rails?
if possible monitor DC voltage when first turned on until that strange things happen, maybe voltage drop or not?
http://www.diyaudio.com/forums/solid-state/238444-testing-locating-filter-capacitor.html
Show us what is AC voltage from the transformer & DC voltage on the rails?
if possible monitor DC voltage when first turned on until that strange things happen, maybe voltage drop or not?
Jaycee,
I will look into these caps next. What makes you think so?
I'm no expert but I don't think it is the power supply, because filter caps read 'out of range' on my meter, so I think it is beyond the 10,000uf max range.
Reassemble everything, rechecked dc bias and this is what I observe for sure.
Hum on all line input unless no line-in connections at all, then no hum. No hum on phono stage. Anemic sound any input.
John Bali,
I'm a novice so where do I check AC voltage and DC on the rails? Thanks
I will look into these caps next. What makes you think so?
I'm no expert but I don't think it is the power supply, because filter caps read 'out of range' on my meter, so I think it is beyond the 10,000uf max range.
Reassemble everything, rechecked dc bias and this is what I observe for sure.
Hum on all line input unless no line-in connections at all, then no hum. No hum on phono stage. Anemic sound any input.
John Bali,
I'm a novice so where do I check AC voltage and DC on the rails? Thanks
C320/C370 are signal coupling caps, so they are directly in the audio path. 10uF will do if getting 4.7uF is awkward.
Testing capacity is not the same as testing ESR (equivalent series resistance). Capacitors can still read a figure within the right ballpark, but have high ESR making them bad at smoothing.
Testing capacity is not the same as testing ESR (equivalent series resistance). Capacitors can still read a figure within the right ballpark, but have high ESR making them bad at smoothing.
Thanks, this is very educational.
I was studying the schematic and the location of these caps. I noticed that when the source direct switch on the volume board is activated the tone controls are out of the circuit. I still have hum and the same sound with a source connected to the 'source direct' input. Would this mean that the problem is further upstream on the input board. Or further downstream after the tone board on the main board A, because there is hum and weak sound on the preamp out as well.
On another note, I've read this amp has a class A input and runs hot, but the heat sinks get so hot you can not even touch them for 5 seconds. Is this normal too.
I was studying the schematic and the location of these caps. I noticed that when the source direct switch on the volume board is activated the tone controls are out of the circuit. I still have hum and the same sound with a source connected to the 'source direct' input. Would this mean that the problem is further upstream on the input board. Or further downstream after the tone board on the main board A, because there is hum and weak sound on the preamp out as well.
On another note, I've read this amp has a class A input and runs hot, but the heat sinks get so hot you can not even touch them for 5 seconds. Is this normal too.
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You seem pretty determined to try and sort this one out
I'll have to look at the circuit later but if you have hum etc when its essentially working as a passive preamp then I would suggest (with the amp OFF) checking continuity from the power amp input grounds all the way back toward the inputs. Also check continuity from the amp power amp inputs back to the volume control.
I still think this sounds more of a physical problem (cracked print etc) as much as anything.
I'll have to look at the circuit later but if you have hum etc when its essentially working as a passive preamp then I would suggest (with the amp OFF) checking continuity from the power amp input grounds all the way back toward the inputs. Also check continuity from the amp power amp inputs back to the volume control.
I still think this sounds more of a physical problem (cracked print etc) as much as anything.
You seem pretty determined to try and sort this one out
I'll have to look at the circuit later but if you have hum etc when its essentially working as a passive preamp then I would suggest (with the amp OFF) checking continuity from the power amp input grounds all the way back toward the inputs. Also check continuity from the amp power amp inputs back to the volume control.
I still think this sounds more of a physical problem (cracked print etc) as much as anything.
I am determined, because some claim this is Sony's best strictly 2 channel amp and sold for $1700 new in '93. I'm getting used to this amp and have pulled every circuit board. I would agree with you about damage and will study it more carefully. Visually there is nothing damaged on any board or component that I have detected. I thought I was going to find something, and need your guys help.
There is a sticker say it was a refurbished unit when original purchased. I noticed that many traces on the control board and main B board have been flowed with solder. I checked continuity and they seem fine, but may have missed something. This may be a type of physical damage that attributes to the problem.
I would have a measure (as I outlined) with the amp in its faulty state. Hairline cracks can be 99% invisible.
Without a scope it all becomes more time consuming as you have to try things to eliminate them, rather than just confirming with a measurement.
You are looking for perfect (zero ohms) conductivity between the signal input ground on the power amp initially back to the volume control and from the volume control back to the input sockets. The signal input to the power amp should also follow with zero resistance (assuming no series components) back to the wiper of the volume control control. The input to the volume control should then find its way back to the input sockets via any switching.
I'll look at the circuit later but try and have a measure.
There are a lot of ways to attack a problem like this but you have to be determined and prepared to try things out. For instance, if you find nothing amiss then hard wiring the power amp inputs to a pot and testing the power amp in isolation would "prove" the power amps are OK.
Without a scope it all becomes more time consuming as you have to try things to eliminate them, rather than just confirming with a measurement.
You are looking for perfect (zero ohms) conductivity between the signal input ground on the power amp initially back to the volume control and from the volume control back to the input sockets. The signal input to the power amp should also follow with zero resistance (assuming no series components) back to the wiper of the volume control control. The input to the volume control should then find its way back to the input sockets via any switching.
I'll look at the circuit later but try and have a measure.
There are a lot of ways to attack a problem like this but you have to be determined and prepared to try things out. For instance, if you find nothing amiss then hard wiring the power amp inputs to a pot and testing the power amp in isolation would "prove" the power amps are OK.
Check for continuity as per blue line. Check the plus and minus 15.6 volts is correct on the opamp. The relays (green) complicate things because I don't know what position they default to with no power applied. As drawn they are correct for a direct input.
You could test with the amp on and no speakers connected. Confirm first that there is no voltage between any two points you are going to do a resistance check on.
You could test with the amp on and no speakers connected. Confirm first that there is no voltage between any two points you are going to do a resistance check on.
Attachments
Measure on two big electrolyte (or anywhere near it), there muse be similar DC on + & - rails... but don't do it if you not sure how to. There are two red circle on Molly's picture above, they are B+ & B- if you can just check & post what meter says on it...
Molly give you better suggestion, bad grounding at input also can cause it. just check continuity from input socket (usually RCA) to main input of the power amp.
Another you can try is to make a new input circuit, only one volume pot & its output direct to amp input. now the hum is there or not.
Note: for safety don't connect your speakers if there any DC offset at speaker's out terminal
I thought this amp has not used for a long time, there maybe cold solder joint on some point. check on socket & terminal that has wire soldered on it, try if the joint are still strong or not
If all okay maybe some resistor(on input board) is broken, the resistance going higher than what it should be
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Reference to ground,
1. + meter's lead to B+ & - meter's lead to ground
2. + meter's lead to ground & - meter's lead to B-
they should be identical...(maybe around 15V or so)
As Molly ask, yes you must check continuity on the blue line should be zero ohm (or zero volt).
If you check voltage on the blue line (15.6 volt on it) yo have broken ground connection between it. Check all traces & or cable on the blue line with meter set to "x1 ohmmeter" you should find unconnected one & that is the problem...
note : continuity test is with unconnected power
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