Note: troubleshooting of large audio amplifiers constructed with discrete output stages is left to a separate document. See: "BIG audio power amps". The audio amplifiers found in small radios, Walkmen, portable cassette recorders, and other low power devices are often single chips with few external components. Obtain a pin diagram, test inputs and output(s) with an audio signal tracer and/or oscilloscope. A dead output where inputs and power are present usually indicate a defective IC - as does one that becomes excessively hot - assuming that the output is not overloaded. Larger audio amplifiers may use ICs (up to 10 or 20 W) or hybrid modules (up to 100 W per channel and beyond). Purists may argue about the quality of the sound from these compared to discrete component designs but they are being used in many designs - at most price points (except perhaps the stratosphere of audiophile land). Hybrids modules (called 'blocks' or 'bricks' by some) may be totally self contained requiring just power and line level inputs or may be just the final stage in an overall system including external amplifier circuitry which is effectively a power op amp - high gain with negative feedback. Failure of these bricks is quite common. Note that testing of these op amp designs - whether discrete or brick based - can be very confusing due to the high gain and feedback. Intermediate signals in a working channel may look like power supply ripple and noise. In a dead channel these same points may appear to be normal or highly distorted audio depending on which stage you test. In addition, since extensive negative feedback is used, power supply ripple and noise is much less important significant and there may be substantial amounts of both in a normally operating amplifier. One of the bricks may be shorted resulting in a blown fuse or overheating of other components. It is usually safe to unsolder each of the hybrids to determine if the other channel or at least other portions of the unit come back to life and without blowing fuses. With stereo amplifiers, it is normally safe - and most effective - to swap components between the working and dead channels as long as you are sure there is no short circuit on the output. This is by far the quickest way to confirm a dead brick. (I would be a lot more reluctant to make this recommendation for a large audio amplifier constructed with discrete transistors in the final power stage as multiple cascade failures are possibly and likely if **all** defective parts are not located before power is reapplied.)
There can be all sorts of sources for low level noise or static including bad connections almost anywhere, defective semiconductors, and erratic power amp modules. These are usually hybrid circuits - multiple devices mounted on a common substrate and interconnected via a variety of technologies. Think of them as entire subsystems encased in plastic. Thus, hybrid bricks may have problems with noise especially considering that they may run hot and be abused by poor tastes in music (or at least high volume levels). Thermal cycling can take its toll on this kind of device. If you have eliminated other likely causes, replacing the brick would be the next step if the module is not that expensive - how much do you value your time and hair? Of course, if there are separate bricks for each channel, one channel is most affected, and the volume control does not affect the level of the noise, the choice is clear - swap. This will be relatively low risk in most cases. A hot air gun used carefully on the final modules might also be a good way of inducing or changing symptoms resulting from marginal connections or components.
(From: Andy Cuffe (email@example.com)). If it has IC's for the audio output you can just remove one of them. If the fuse still blows try removing the other one. If the fuse blows with both output ICs out you know there are problems in an other part of the unit, probably the power supply. If it uses transistors instead of ICs you just need to check them with an ohmmeter. The bad ones almost always measure close to 0 ohms between at least 2 of the three pins. Once you find the bad pair try the stereo with them removed. You should get normal sound from the channel with the good transistors. To determine if there is more damage to the amplifier you can swap the good transistors into the damaged channel. Before you remove anything WRITE DOWN where they go because it's easy to get them mixed up. I strongly recommend that you don't bypass the fuse unless you don't want to fix it very much. I have seen a lot of repairable electronics ruined by this type of troubleshooting.
(From Daan van der Veer (D.J.C.vanderVeer@stm.tudelft.nl)). I have good experiences with the use of Darlingtons instead of normal output transistors in audio power amplifiers. The only problem is that you have to readjust the bias current of the bases of the drivers. Furthermore, reduced or increased frequency response is almost always corrected by the amplifier's feedback. Readjusting the bias current is very simple with a scope and a sine wave generator, but could also be done with a simple voltmeter. And a computer is a very handy tool in diagnosing amps, if you have a soundcard, you can (mis)use it to measure a frequency response of any everyday amp (frequency response of most soundblaster compatible soundcards is 44 kHz). And with a very precisely tuned high quality notch filter you can even measure the THD of any amp, *real-time*. (This is very handy if you want to adjust output transistor bias current, to a minimum of crossover distortion).
Symptoms include audible noise when rotating knobs, erratic operation of mode selectors, random changes in volume, switches, or controls that need to be jiggled or tapped to make them cooperate. The causes are likely to be either dirt or wear. First, try a spray control/contact cleaner - even the stuff from Radio Shack may make a remarkable difference iff (1) dirt is the problem and (2) you can get the cleaner inside the troublesome part. DO NOT use WD40 or a similar product because aside from the flammability issues their use may result in rapid failure even if you get the immediate gratification often provided by these sprays. See the section: "Why NOT to use WD40 on noisy controls". Some types of contact and control cleaners can be used safely with low voltage circuits while they are powered but not always - read the label directions. Select a product that specifically states that is it safe for switches and controls. Use the extension tube that comes with the spray can and snake it into or near any visible access holes. Operate the control or switch to help the cleaning action. Don't overdoe it - if you get to the right spot, a little is all that is needed. Resist the urge to use sandpaper or steelwool (ack!) on switch or connector contacts. However, pulling a piece paper through a set of contacts or the occasional gentle use of a soft pencil eraser (e.g., Pink Pearl) may be helpful. If this does not help - or only helps short term - the part may be worn. Sometimes, repair is possible (a slide switch with contacts that have loosened with use, for example) but replacement is better - if you can find an exact or suitably close match. See the section: "Interchangeability of components".
This may not apply to the resistive elements in all/many/most controls but why risk it?: (From: Richardson (firstname.lastname@example.org)). Here are some facts after seeing the results first hand in an environment where Pro TV editors were using up controls in audio mixers manufactured by Shure Brothers. WD40 when used for the first time resulted in good operation for 5 days. After that time the controls started to deteriorate very quickly and were junk the next week. The situation was clear after opening up the pots afterward. The carbon material was bonded to itself and to the phenol substrate by some chemical which became soft after being exposed to the hydrocarbon base of the WD40. It soon deteriorated to mush. The use of LPS 1 did not cause such a dramatic failure of the surfaces but did not provide any improvement that lasted. In the past we could get good results with Freon cleaning spray, but it is getting harder to get than the replacement controls. In test pots the only way to get an improvement was to carefully remove residue and relubricate with a lubricant like Radio Shack "Gel Lube" or the latest Sony grease available for broadcast and pro use.
(From: Rene Zuidema (email@example.com)). Often, pots are not really dirty, but the pot wiper just worn out the resistive layer. No amount of cleaning will solve the problem. Just carefully re-bend the wiper contacts to follow another track alongside the damaged resistive material. If done well, the wiper will now track intact resistive material again. As new! This specially works for servo's as used in RC cars / planes etc. In these applications the resistive track around the servo neutral position is worn out after some seasons of use. (From: Paul Weber (firstname.lastname@example.org)). Disassemble the pot by carefully bending the tabs that hold the cover on (assuming this is a cheap consumer type pot). Inspect the works with a magnifying glass; find the fingers on the rotor that touch the resistor material. Using a needle or dental pick carefully bend the fingers out of the furrow they've worn in the resistor material. Objective is to make contact with an unworn area on the resistor material. Clean the whole thing with spray cleaner and re-assemble. Overall resistance may be slightly changed due to the lost resistance material, but this is usually not a problem in consumer applications. Good luck!
Any intermittent problems that cause random sudden changes in performance are likely due to bad connections, internal connectors that need to be cleaned and reseated, or dirty switches and controls. First, see the section: "Noisy or intermittent switches and controls". Bad solder joints are very common in consumer electronic equipment due both to poor quality manufacturing where cost reduction may be the most important consideration. In addition solder connections deteriorate after numerous thermal cycles, vibration, and physical abuse. Circuit board connections to large hot parts or parts that may have mechanical stress applied to them are most likely be suffer from hairline solder fractures (often called 'cold solder joints' when they result from poor quality soldering at the time of manufacture). However, since the solder is often the only thing anchoring these components, mechanical stress can eventually crack the solder bond as well. To locate cold solder joints, use a strong light and magnifier and examine the pins of large components and components that are subject to physical stress (like headphone jacks and power connectors) for hairline cracks in the solder around the pin. Gently wiggle the component if possible (with the power off). Any detectable movement at the joint indicates a problem. A just perceptible hairline crack around the pin is also an indication of a defective solder connection. With the power on, gently prod the circuit board and suspect components with an insulated tool to see if the problem can be effected. When in doubt, resolder any suspicious connections. Some device may use double sided circuit boards which do not have plated through holes. In these cases, solder both top and bottom to be sure that the connections are solid. Use a large enough soldering iron to assure that your solder connection is solid. Put a bit of new solder with flux on every connection you touch up even if there was plenty of solder there before. In addition to soldering problems, check for loose or corroded screw type ground (or other) terminals, and internal connectors that need to be cleaned and reseated.
If at times, it is necessary to turn the volume way up or possibly to tap or whack the unit to get the sound in one or both channels to come on when the unit is first powered up, the speaker protection relay could be faulty. Receivers and audio amplifiers often include a set of relay contacts in series with each output to protect the loudspeakers from power-on and power-off transients as well as damage due to a fault in the audio circuits. However, these contacts may deteriorate after awhile resulting in intermittent sound. While this set of symptoms could be the result of general bad connections or even dirty controls or switches, the relay is often at fault. This is exacerbated by switching the unit on and off at high volume levels as well as this may cause contact arcing. To determine if the relay is at fault, either test it as outlined in the section: "Relay testing and repair" or with the unit on, very gently tap the relay to see if the sound comes as goes. If the relay is bad, you can try cleaning its contacts or replace with one that has similar electrical specifications as long as you can mount is somehow. Don't be tempted to bypass the relay as it serves a very important protective function for both the amplifier and your loudspeakers. If it is not the relay, see the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".
You turn on your stereo receiver and everything appears normal - display, tuning, signal strength, etc., but there is no sound. A few minutes later, just when you had entirely given up any hope, there is a click and everything is normal - until the next time you power down. The amplifier is taunting you - hehe, I will come on when I feel like it! (Note that if it never comes on, then there could be a real problem that the protection circuitry is catching such as shorted components in one of the power amplifiers.) This sounds like the signal to power the speaker relays is not being generated. The underlying cause could be a fault in the time delay or fault protection (overload) circuit. It could be as simple as a bad capacitor. A first test might be to check for an audio signal at the input to the speaker relay. If there is signal almost as soon as you power it up, then trace back from the relay coil to see what type of circuitry is there. A schematic will probably be needed unless you find an obvious bad connection or dried up capacitor.
(From: Frank Fendley (email@example.com)). It sounds like the protection circuit (usually a relay) is cutting in during louder music passages. This is caused by an imbalance in the amplifier circuitry, generally resulting in a DC offset voltage appearing on the output. The usual cause is a defective transistor(s), probably in the earlier stages in this case. Of course, it could also be that you have 10 sets of speakers connected to the amplifier and all the volume levels turned to the stops - it is simply protecting itself from abuse! :-) --- sam.
(From: Ronald Dozier (firstname.lastname@example.org)). The protection relay usually detects DC offset at the speaker terminals and then open's the speaker leads. Check for a DC offset > 100 mV or so before at the output, before the protection relays. Leaky outputs are the first to suspect. In most PP drivers the voltage between the bases of the output transistors should be about 2 Vbe or around 1.2 volts. 0V is definitely a problem. I have only seen one amp (mine) that used 4 Vbe. or about 3.2 volts. The voltage across the emitter resistors without a load are in the 0 to 20 mV range. This voltage should not increase appreciably over time and is set with the bias adjustment. Careless playing with the bias pot will result in output transistor destruction. It is best set with the aid of a distortion analyzer. All resistors/transistors in the driver and output stage and in some cases the pre-amp are all suspect. The small valued ones like to change value. Compare with functioning channel.
Unlike big amplifiers, these are not normally failures caused by abuse or high power components. This type of equipment includes preamps, cassette decks, CD players, tuners, etc. First, eliminate the audio patch cables by trying a different set or swapping left and right at both ends. In addition, confirm that your amplifier is operating on all cylinders (or channels). Assuming this does not turn up anything: For a tuner, the problem is almost certainly very near the output - probably a bad connection, bad jack, or bad final IC or transistor stage. There isn't much between the demodulator and the line output. For a tape deck, much more can be involved. First, clean any mechanical REC/PLAY mode and other switches with contact cleaner as dirty contacts may result in one channel dropping out. If this does not help, determine if the output of the tape head is making it to the toutput by touching the terminals on the playback head with a tiny screwdriver when in play mode - you should get a hum when you are on the appropriate signal wire. If there is none for the bad channel, then you will have to either trace forward from the head or backward from the output. If you do hear a hum in the defective channel, the tape head itself may be bad - shorted or open - very dirty. Older tuners, receivers, premaps, tape decks, etc. used discrete transistors and circuit tracing was possible. Modern equipment relies on ICs but pinouts, at least, are generally available by checking a cross reference guide such as those put out by ECG, NTE, or SK. Again, first eliminate bad jacks or cables -- and with tape decks - clean the REC/PLAY (and other) mode selector switches.
Assuming there are no other symptoms and the sound is coming from inside the unit and not the loudspeakers, this is probably simply due to vibrating laminations in the power transformer or motor(s) or nearby sheetmetal that is affected by the magnetic fields from the power transformer or motor(s). Most of the time, this is harmless but can definitely be quite annoying especially when one expects total silence from their audio equipment. If the noise is coming from any motors or their vicinity, refer to the section: "Motor noise in audio equipment". Sometimes, simply tightening the screws that hold the transformer or motor together or the mounting screws will be all that is needed. Placing a toothpick or piece of plastic in a strategic location may help. It is also possible to coat the offending component with a varnish or sealer suitable for electronic equipment but be careful not to use so much that cooling is compromised or getting any in bearings or locations that would interfere with rotating parts. Dirty power - a light dimmer on the same circuit - may also result in increased magnetic noise. See the section: "Dirty power and buzz from equipment". If the hum or buzz is in the audio, there could be a bad filter capacitor in the power supply, other power supply problems, bad grounds inside the unit or general ground problems with external equipment, or other bad connections. Disconnect all external devices (except the speakers if you do not have a pair of headphones) and determine if the problem still exists. Proceed accordingly. Some Sony receivers are known to develop bad grounds internally and just tightening the circuit board mounting screws and/or resoldering ground connections will cure these. Overloads can also cause a hum or buzz but would generally result in other symptoms like a totally or partially dead amplifier, severe distortion, smoke, six foot flames, etc. If the problem is only annoying when the equipment is not in use, as a last resort (where no memory or clock functions run off the AC line), putting in an AC line switch may not be such a bad idea.
Power line waveforms that are not sinusoidal can cause buzz. Multiple devices on the same circuit (or even different circuits) can interact. A TV or other equipment may add to the problem since its switching power supply draws current only on part of each cycle. Excessive voltage can also increase the 'magnetic noise' from motors and power transformers. This sound is a result of core or winding vibrations. You need to check for both of these possibilities - a calibrated scope is best. DMMs and VOMs may not read correctly with non-sinusoidal waveforms.
Although this is a rather special application, similar problems and solutions apply to other interference problems. Also see the section: "Interference on AM radio band". "I am using a 12V DC to 110 VAC converter in my car, to run a small TV/VCR. It works fine. But the TV speaker is not very good. So I got one of those cassette adapters that has an audio cassette on one end, and a headphone jack on the other. I plug that into the TV, and the cassette slot on my car stereo. So then I can hear the TV sound on the car speakers, which are much better speakers. But now there is a lot of high frequency noise that way, on the car speakers. It is very irritating. A high frequency buzz of some kind. How can I reduce or eliminate that noise?" (From Duncan (email@example.com)). First we have to figure out where it is coming from. The inverter is certainly a noise source, and without spending a large sum for a well filtered inverter you have to deal with the noise somehow. One possibility is that the noise is on the 12 volt power supply going to your car stereo. To test for this, play a blank tape while running the TV and listen for the same noise. Fix with filters on the power leads of stereo and/or inverter, wire to a solid clean rail very close to the battery. Another possibility is capacitive coupling between the TV, connected to the higher voltage side of your inverter, and the tape deck's playback heads. This might be alleviated by using a different, more isolated inverter or by using another method of getting the audio into the stereo system. FM modulators intended for portable CD players might work. Another possibility is that the power supply of the television is not rejecting the higher frequency components of the inverter's signal. The fix here would be to add more capacitors and perhaps resistive or inductive filter elements inside the television. Check this by plugging headphones into the same jack and listening for the noise. Still another possibility is that the noise you hear is part of the horizontal sync signal, which is not rejected well by all televisions. This causes a high pitched continuous squeal which is inaudible to some people. The only easy work-arounds here would be to try a different television or to turn down the treble or select Dolby-B on your car stereo. To test for this effect, try the same hookup in your house with your home stereo, cassette deck, adaptor cassette, and television. Or just hook up your HiFi stereo VCR to the home stereo, move the whole mess into the car, and ignore the car stereo. Four of Radio Shack's little Pro-7 speakers with a Marantz 25 watt by four channel amplifier worked quite well for me, especially when combined with a hand-held LCD monitor :-).
This sort of problem is usually in the form of a buzz or hum at 60 Hz or 120 Hz (or 50 Hz or 100 Hz if your power is at 50 Hz). There may be a little of this on a small portion of the AM band but if it is excessive and interferes with even strong stations, then a remedy is needed! The following approach should serve to locate the source if it isn't obvious: (From: Doug (firstname.lastname@example.org)). First, turn off the main house breakers and listen on AM with a battery operated portable radio. If the noise has disappeared, then you are generating the interference in your own home and its time to check out things like light dimmers, fluorescent lamps, touch-control incandescent lamps, motors, even cordless phones, etc. If the interference is still present on the portable AM radio, with the breakers off, walk around the perimeter of the house and see if it's loudest near the electric service entrance. If it is, walk up and down the street and try to see if the intensity varies (your neighbors will think you're weird - but what the heck!). If the interference comes from outside of your home, it's time to call the electric utility company and ask to speak with one of their engineers. The electric industry is required by the U.S. FCC. to keep radio interference (RFI) to a minimum. They may try to stonewall you but if you persist, they will sent out an engineer with radio direction finding equipment to locate the source of the interference. If the source is a piece of equipment on a non-cooperative neighbor's property, you may have another problem - but - one step at a time. I've been through this procedure several times. Last time, the electric company engineer tracked it to a broken and arching pole insulator. As a former AM broadcast engineer (and current HAM radio operator), I've experienced this problem enough to know that while challenging, the interference source can always be found. (From: Mr Fixit (email@example.com)). Radio Shack sells RF chokes. Label says "SNAP-ON FILTER CHOKES (2) cat. no. 273-104" They open up and snap together over your wires. Very simple to install and come with comprehensive instructions. With a little experimentation you can see if you need it on your power cord, on the speaker wires or both. (these wires can act as antennas for certain frequencies of RFI) I use them all over my house on phones, TV's, stereos, computer speakers etc to block out RFI from my CB base station and vis-versa. BTW: if you happen to have any unneeded computer monitor cables laying around, the oversize collar near the end is a RF choke. I had a couple so I cut the covering and slid them off the cable. I put them onto our cordless phone base unit antenna as an experiment to see if it would reduce the ever-present buzz it had. To my surprise, the buzz disappeared with no loss of signal strength. (From: Dan Hicks (firstname.lastname@example.org)). An even better idea is to put these chokes on the RF **generators** in your house. I'm not sure if it's "code" to install them on permanent wiring, but it should be safe to do so so long as you are reasonably careful. And it's easy to install them on any plug-in devices that appear to cause problems.
Power surges or nearby lightning strikes can destroy electronic equipment. However, most of the time, damage is minimal or at least easily repaired. With a direct hit, you may not recognize what is left of it! Ideally, electronic equipment should be unplugged (both AC line and phone line!) during electrical storms if possible. Modern TVs, VCRs, microwave ovens, and even stereo equipment is particularly susceptible to lightning and surge damage because some parts of the circuitry are always alive and therefore have a connection to the AC line. Telephones, modems, and fax machine are directly connected to the phone lines. Better designs include filtering and surge suppression components built in. With a near-miss, the only thing that may happen is for the internal fuse to blow or for the microcontroller to go bonkers and just require power cycling. There is no possible protection against a direct strike. However, devices with power switches that totally break the line connection are more robust since it takes much more voltage to jump the gap in the switch than to fry electronic parts. Monitors and TVs may also have their CRTs magnetized due to the electromagnetic fields associated with a lightning strike - similar but on a smaller scale to the EMP of a nuclear detonation. Was the unit operating or on standby at the time? If was switched off using an actual power switch (not a logic pushbutton), then either a component in front of the switch has blown, the surge was enough to jump the gap between the switch contacts, or it was just a coincidence (yeh, right). If it was operating or on standby or has no actual power switch, then a number of parts could be fried. Many devices have their own internal surge protection devices like MOVs (Metal Oxide Varistors) after the fuse. So it is possible that all that is wrong is that the line fuse has blown. Remove the case (unplug it!) and start at the line connector. If you find a blown fuse, remove it and measure across the in-board side of fuse holder and the other (should be the neutral) side of the line. With the power switch off, this reading should be very high. With the switch on, it may be quite low if the unit uses a large power transformer (a few ohms or less). For example (assuming power transformer operated supply): * Small AC adapter - 100 to 500 ohms. * Large AC adapter - 10 to 100 ohms. * VCR - 15 to 30 ohms. * Cassette deck or CD player - 25 to 100 ohms. * Stereo receiver or amplifier - .5 to 10 ohms. Some may be outside these ranges but if the reading is extremely low, the power transformer could have a partially or totally shorted primary. If it is very high (greater than 1 K ohms), then the primary of the power transformer may be open or there may be blown thermal fuse under the outer insulation wrappings of the transformer windings. This may be replaceable. If the unit has a switching power supply, see the document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies". If the resistance checks out, replace the fuse and try powering the unit. There will be 3 possibilities: 1. It will work fine, problem solved. 2. It will immediately blow the fuse. This means there is at least one component shorted - possibilities include an MOV, line filter capacitor, transformer primary. 3. It will not work properly or still appear dead. This could mean there are blown fuses or fusable resistors or other defective parts in the power supply or other circuitry. In this case further testing will be needed and at some point you may require the schematic.
Should you always use a surge suppressor outlet strip or line circuit? Sure, it shouldn't hurt. Just don't depend on these to provide protection under all circumstances. Some are better than others and the marketing blurb is at best of little help in making an informed selection. Product literature - unless it is backed up by testing from a reputable lab - is usually pretty useless and often confusing. Line filters can also be useful if power in you area is noisy or prone to spikes or dips. However, keep in mind that most well designed electronic equipment already includes both surge suppressors like MOVs as well as L-C line filters. More is not necessarily better but may move the point of failure to a readily accessible outlet strip rather than the innards of your equipment if damage occurs. It is still best to unplug everything if the air raid sirens go off or you see an elephant wearing thick glasses running through the neighborhood (or an impending lightning storm).
(From: Fred Noble (email@example.com)). A large number of users still seem confused about the use of a Surge Suppressor in line with a UPS. The general rule is, do NOT plug a surge suppressor INTO the OUTPUT of a UPS that produces a non-sinewave output that exceeds 5% Total Harmonic Distortion (or THD) when the UPS operates from battery supporting any load under any ambient conditions. Do NOT plug a Line Conditioner or other type of filter into the UPS either. You can plug a UPS into a well grounded surge suppressor, but this is not always a good idea, especially when we are talking about various 'low cost' surge suppressors of questionable electrical integrity. We constantly hear of low-end surge suppressor recalls for safety reasons, with several recent recalls ordered by the U.S. Consumer Product Safety Commission, for example, http://cpsc.gov/cpscpub/prerel/prhtml97/97078.html. A cursory search using the keywords 'surge arrester consumer recalls' with the Excite engine reveals several such recalls. If the surge suppressor you plug the UPS *into* is electrically 'safe' you are still extending the ground path with such a cascading arrangement, which, on balance, may not be wise. The UPS should provide Surge Suppression energy ratings of 480 Joules or more. Then, you probably wouldn't require the additional upstream surge suppressor at all. This does not mean that you shouldn't also have a surge suppressor installed at the MAINS or the branch panel, however. We are only talking about the extra, stand-alone, AC protection devices. This is also not to say that you should not provide additional surge suppression for your modem or UTP connections!. This you must do, and a low cost device that is also a *high quality* device, should be used. These devices are designed specifically for the protection of DC electrical surges and they are not used in series with a UPS anyway.Go to [Next] segment
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