I have a Kenwood KR-A4040 stereo receiver that I've had for a long time and now finaly something went bad with it some smoke came out and blew the fuse. I replaced the fuse and tried turning it back on and it blew the fuse again! I took a look inside and I could not find anything out of order physicaly, however I'm good with a DMM and a solder iron. I'd like to fix it if I can I'm still buying a new thought 
. This was one great receiver when it was working excelent! But I don't know what caused it to fail? I also forgot to say when it powered on with the fuse before the second fuse blew a resistor had a orange glow then the fuse popped. Any help would be greatly apreciated, I just don't want to throw this away.
. This was one great receiver when it was working excelent! But I don't know what caused it to fail? I also forgot to say when it powered on with the fuse before the second fuse blew a resistor had a orange glow then the fuse popped. Any help would be greatly apreciated, I just don't want to throw this away.In any solid state amp, if it blows fuses hard, it is usually a pretty safe bet that the output stage of the power amp has blown one channel. I don't know that recei9ver, I am sure you can find teh schematic, but looking inside, you either have discrete output transistors on heat sinks, or there is one or two power amp ICs. COuld be one IC per channel or some ICs are stereo in one package.
Look for the heat sink in the amp. If there is a dark colored block screwed to it with 10-15 legs soldered to the board, that is a power IC.
A lot less common but still possible is a shorted rectifier in the power supply.
And way less common than even that, but still possible, a shorted filter capacitor.
And other things are still possible and even WAY less likely. For example I see darn few bad power transformers in things like this.
Since a resistor has burned up, more will be wrong than just the transistors or ICs. That resistor that got hot enough to glow needs to be replaced at the very least.
I use a lot of different places for parts, but someplace like MCM would probably have any transistor or IC it needs if such parts are still on the market. B&D Enterprises sometimes has odd ones.
MCM Electronics: Home and Pro Audio/Video, Security and Test Equipment
B&D Enterprises - Electronic Components Distributor
Look for the heat sink in the amp. If there is a dark colored block screwed to it with 10-15 legs soldered to the board, that is a power IC.
A lot less common but still possible is a shorted rectifier in the power supply.
And way less common than even that, but still possible, a shorted filter capacitor.
And other things are still possible and even WAY less likely. For example I see darn few bad power transformers in things like this.
Since a resistor has burned up, more will be wrong than just the transistors or ICs. That resistor that got hot enough to glow needs to be replaced at the very least.
I use a lot of different places for parts, but someplace like MCM would probably have any transistor or IC it needs if such parts are still on the market. B&D Enterprises sometimes has odd ones.
MCM Electronics: Home and Pro Audio/Video, Security and Test Equipment
B&D Enterprises - Electronic Components Distributor
It has descrete out transistors label numbers on them are "C4467 SK" "A1694 SK" then there's two more that are the same label numbers and the resistor
that was glowing orange is a 0.22KX2 and has the ohm symbol near the '0.22' it has threw legs and is rectangular and white.
Classic case of failed outputs by the sound of it. Measure those transistors you mentioned above on ohms and also on diode check on your DVM and they will probably read 0.00 (short). Measure center leg to the other two in turn
Will I need to test them in the circuit or out of the circuit? And also is there any kind of IC that turns on the display screen on the receiver? Because when I tried to turn it on nothing turned on just a glowing resistor and that's about
it. I'm assuming it has to do with the output stage with a set of shorted outputs maybe the other pair?? But ill test them and anything else.
It would really help to see a circuit. Good close up pictures of the output stage would help too.
You will probably find one channel OK.
If you remove the faulty output transistors the amp should power up normally.
It's highly likely that the driver transistors have failed too.
It worth checking carefully for dry joints etc on anything this age, particularly on any transistors/regulators that run hot.
You will probably find one channel OK.
If you remove the faulty output transistors the amp should power up normally.
It's highly likely that the driver transistors have failed too.
It worth checking carefully for dry joints etc on anything this age, particularly on any transistors/regulators that run hot.
'
Yup
You will be needing to replace at least 4 or 5 transistors on that channel if yer lucky. Plus we still don't know what caused the original failure yet. But certainly replacing the fuse after you've seen smoke wasn't too good on parts.
Not sure if you have the tools, test gear, time , and know how. You can spend the bucks trying to repair it, and then still end up paying more than if you didn't touch it. I know I'd charge 2X seeing a botched repair attempt. If you really want to keep the gear or learn a little of this skill is up to you.
You will need to locate a schematic first and then determine if suitable replacement devices and resistor can be had.
That's what I had in mine but the screen will not display anything if I try powering it up for a split second. I was wondering if there is any kindnof driver ic that controls the screen display or is it because the output is shorted. Also this particular amplifier has six transistors four big ones and two smaller ones screwed to the heat sink. But what if I disconnect the shorted side will it atleast power up again normaly because one side gets hot. I'll get some
close up pictures for you to check out just gimme a sec. Thanks
Maybe this will help
Hi, don't know if you've found the schematics, but maybe this one will help:
Kenwood KRA4050 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
It seems to be a similar model, as the output stage uses the same transistors you have there in your amp (2SC4467 and 2SA1694). Maybe your 4040 is a bit more simple than this 4050.
Did you compare both channels output transistors readings? If one of them is found to be good, it will guide your searches for bad parts.
Ask user SAKIS, and also search his threads. He has posted a complete guide to repair such equipment.
All the best,
Max.
Hi, don't know if you've found the schematics, but maybe this one will help:
Kenwood KRA4050 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
It seems to be a similar model, as the output stage uses the same transistors you have there in your amp (2SC4467 and 2SA1694). Maybe your 4040 is a bit more simple than this 4050.
Did you compare both channels output transistors readings? If one of them is found to be good, it will guide your searches for bad parts.
Ask user SAKIS, and also search his threads. He has posted a complete guide to repair such equipment.
All the best,
Max.
Hi!
Using the circuit diagram linked to in Maqmber Smartx21's post:-
1) First of all remove both pairs of output transistors from the Amplifier PCB, and test them usinbg a good quality DVM with a Diode Test Range for short circuits between the legs. A good one will read 0.600 to 0.700 V on the diode test range in ONE DIRECTION only - in the other direction the meter will show an over-range indication. If you gert a reading between any legs in BOTH directioins the transistor is short-circuited and MUST be discarded.
2) Next you must determine the cause of failure! This could be:-
a) Defective speaker or shorted wiring etc;
b) Failure of the bias - current adjustment preset;
c) Failure of devices earlier in the circuit;
d) Leakage in capacitors causing previous stages to run into overcurrent;
e) Inadequate heatsinking;
f) Mickey-Mouse transistors!!!
a) Defective Speaker or shorted wiring:-
The remedy for this is obvious!!! If you have a small cheap transistor radio available you can check each speaker scross the radio's speaker o/p for a short period, you will need to disconnect the portable's internal LS to carry out this test tho!!! Listen for any sounds of rubbing or distortion - the speech-coil can overheat and jam if over-driven or used with heavy bass transients, which can abrade its enamel insulation and cause a partial or complete short circuit!!! If you have wiring under carpets, furniture etc., etc., then its insulation may have got damaged or crushed causing an intermittent short across the leads - the remedy for this is obvious!!!
Finally, if you have a 4R/8R speaker impedance switch as per the one shown on the linked circuit, this MUST be set to match the loudspeakers in use as this switch is used to select the correct voltage tappings from the mains transformer HT secondary!!!
b) Failure of the Bias - cirrent adjustment preset:
Nearly all of these receivers have ventilation slots in the tops of their cases, and dust can settle on the top of the amplifier board and eventually result in the wiper of the bias - current preset (VR201/VR202 "Idle adjust") making a poor contact with its track, which will cause the maximum turn-on bias for the driver/output pair to be developed, which will rapidly cause "thermal runavay" and destroy them, if not immediately, it may do so when a signal is applied!!! These presets are vitally important, DON'T attempt to clean them, its best to fit new ones!!! Unfortunately equipment of this age tends to use a pcb-mount preset of an odd size making replacement difficult - a 0.5W cermet-preset with wire-ended leads from Farnell may have to be fitted!!!
You may also have to replace the resistor packs CP1/CP2 (2 x 0.22R 3W) with individual resistors - I've often seen these three - leg ceramic thingys and they're impossible to get hold of, so you'll have to use your ingenuity to replace them!!! Once you've completed the repairs, first of all you MUST turn the bias controls to MINIMUM resistance and allow the amplifier to warm up for 15 minutes, then VR201/VR202 must be set for a standing DC Voltage drop of about 12mV DC across each 0.22 resistor!!!
c) Failure of devices earlier in the circuit:
These amplifiers are direct-coupled all the way back to Q201 - in fact the whole circuit is basically a simplified power op-amp - but in particular you must check Q207, Q209, Q213 and Q215 in particular (and the corresponding equivalents in the second channel if both are defective) - you may be able to get the transistors from eBay or Dial Electronics in the UK.. I would NOT attempt to use European transistors in this type of unit as type of circuit tend to be closely designed to the transistor's current-gain parameters, and if you fit odd substitutes it may well all blow up again!!!
d) Leakage in capacitors causing previous stages to run into overcurrent:
In the circuit given, C208 and C210 are especially critical in this respect and leakage in these two components will upset the current -balance in the input differential pair Q201/Q202 which will alter all the current distribution throughout the amplifier!!! Replace the following with good quality 105C replacement capacitors - C201, C202,C208, C210, C224 & C301.
e) Inadequate heatsinking:
The manufacturer will have provided a large heatsink that is normally adequate for domestic use, but as a rule it's not rated for pumping out umpteen watts of thumping heavy bass music!!! In addition, the heatsink compound originally used by the makers dries up and turns into a hard stuff like paper ****-up cream which is useless!!!
You may have to unscrew the heatsink assemly from both the Amplifier PCb and chassis to clean it properly with isopropyl alcohol and I would strongly recommend you do so, in addition, examine the mica insulating washers very carefully, replacing any that show splits or flaking. I'm assuming the transistors are of the large TO-247 plastic with a metal tab type, whis was generally used on equipment of this age - you should be able to get the mica washers from Farnell!!!
f) Mickey-Mouse transistors:
Don't laugh - unfortunately this is getting more and mre common these days, as the original device manufacturer (Sanken) either takes the devices out of production or charges ruinous prices for them, so you get knock-off devices produced to the lowest specification possible, which are cleverly remarked to fool an unsuspecting purchaser (or even supplier in some cases!!!) - and in nearly every case these counterfeits will destroy themselves long before anything like the rated power output of the amplifier is reached!!!
I wouls either seek advice from other Members before buying new O/P transistors if you can!!! I had to repair a Sony TA-2650 about 18 years ago and the oriuginal Sony devices were unobtainable, biut I used Toshiba Devices from Farnell which proved satisfactory!!! Get an up-to-date Farnell catalogue and ring their technical help line, asking for their suggestion for a complementary pair of bipolar O/P devices suitable for a +/-60V power supply and 100W output.
The situation with regard to O/P devices is changing all the time because of the proliferation of fakes, so you need expert advice before purchase!!!
See:-
sound.westhost.com/fake/counterfeit-p3.htm
Sorry for such a long post, these Kenwood units of this vintage are well worth reconditioning and my aim is to assist in getting your unit going with minimum gamage to your wallet!!!
Using the circuit diagram linked to in Maqmber Smartx21's post:-
1) First of all remove both pairs of output transistors from the Amplifier PCB, and test them usinbg a good quality DVM with a Diode Test Range for short circuits between the legs. A good one will read 0.600 to 0.700 V on the diode test range in ONE DIRECTION only - in the other direction the meter will show an over-range indication. If you gert a reading between any legs in BOTH directioins the transistor is short-circuited and MUST be discarded.
2) Next you must determine the cause of failure! This could be:-
a) Defective speaker or shorted wiring etc;
b) Failure of the bias - current adjustment preset;
c) Failure of devices earlier in the circuit;
d) Leakage in capacitors causing previous stages to run into overcurrent;
e) Inadequate heatsinking;
f) Mickey-Mouse transistors!!!
a) Defective Speaker or shorted wiring:-
The remedy for this is obvious!!! If you have a small cheap transistor radio available you can check each speaker scross the radio's speaker o/p for a short period, you will need to disconnect the portable's internal LS to carry out this test tho!!! Listen for any sounds of rubbing or distortion - the speech-coil can overheat and jam if over-driven or used with heavy bass transients, which can abrade its enamel insulation and cause a partial or complete short circuit!!! If you have wiring under carpets, furniture etc., etc., then its insulation may have got damaged or crushed causing an intermittent short across the leads - the remedy for this is obvious!!!
Finally, if you have a 4R/8R speaker impedance switch as per the one shown on the linked circuit, this MUST be set to match the loudspeakers in use as this switch is used to select the correct voltage tappings from the mains transformer HT secondary!!!
b) Failure of the Bias - cirrent adjustment preset:
Nearly all of these receivers have ventilation slots in the tops of their cases, and dust can settle on the top of the amplifier board and eventually result in the wiper of the bias - current preset (VR201/VR202 "Idle adjust") making a poor contact with its track, which will cause the maximum turn-on bias for the driver/output pair to be developed, which will rapidly cause "thermal runavay" and destroy them, if not immediately, it may do so when a signal is applied!!! These presets are vitally important, DON'T attempt to clean them, its best to fit new ones!!! Unfortunately equipment of this age tends to use a pcb-mount preset of an odd size making replacement difficult - a 0.5W cermet-preset with wire-ended leads from Farnell may have to be fitted!!!
You may also have to replace the resistor packs CP1/CP2 (2 x 0.22R 3W) with individual resistors - I've often seen these three - leg ceramic thingys and they're impossible to get hold of, so you'll have to use your ingenuity to replace them!!! Once you've completed the repairs, first of all you MUST turn the bias controls to MINIMUM resistance and allow the amplifier to warm up for 15 minutes, then VR201/VR202 must be set for a standing DC Voltage drop of about 12mV DC across each 0.22 resistor!!!
c) Failure of devices earlier in the circuit:
These amplifiers are direct-coupled all the way back to Q201 - in fact the whole circuit is basically a simplified power op-amp - but in particular you must check Q207, Q209, Q213 and Q215 in particular (and the corresponding equivalents in the second channel if both are defective) - you may be able to get the transistors from eBay or Dial Electronics in the UK.. I would NOT attempt to use European transistors in this type of unit as type of circuit tend to be closely designed to the transistor's current-gain parameters, and if you fit odd substitutes it may well all blow up again!!!
d) Leakage in capacitors causing previous stages to run into overcurrent:
In the circuit given, C208 and C210 are especially critical in this respect and leakage in these two components will upset the current -balance in the input differential pair Q201/Q202 which will alter all the current distribution throughout the amplifier!!! Replace the following with good quality 105C replacement capacitors - C201, C202,C208, C210, C224 & C301.
e) Inadequate heatsinking:
The manufacturer will have provided a large heatsink that is normally adequate for domestic use, but as a rule it's not rated for pumping out umpteen watts of thumping heavy bass music!!! In addition, the heatsink compound originally used by the makers dries up and turns into a hard stuff like paper ****-up cream which is useless!!!
You may have to unscrew the heatsink assemly from both the Amplifier PCb and chassis to clean it properly with isopropyl alcohol and I would strongly recommend you do so, in addition, examine the mica insulating washers very carefully, replacing any that show splits or flaking. I'm assuming the transistors are of the large TO-247 plastic with a metal tab type, whis was generally used on equipment of this age - you should be able to get the mica washers from Farnell!!!
f) Mickey-Mouse transistors:
Don't laugh - unfortunately this is getting more and mre common these days, as the original device manufacturer (Sanken) either takes the devices out of production or charges ruinous prices for them, so you get knock-off devices produced to the lowest specification possible, which are cleverly remarked to fool an unsuspecting purchaser (or even supplier in some cases!!!) - and in nearly every case these counterfeits will destroy themselves long before anything like the rated power output of the amplifier is reached!!!
I wouls either seek advice from other Members before buying new O/P transistors if you can!!! I had to repair a Sony TA-2650 about 18 years ago and the oriuginal Sony devices were unobtainable, biut I used Toshiba Devices from Farnell which proved satisfactory!!! Get an up-to-date Farnell catalogue and ring their technical help line, asking for their suggestion for a complementary pair of bipolar O/P devices suitable for a +/-60V power supply and 100W output.
The situation with regard to O/P devices is changing all the time because of the proliferation of fakes, so you need expert advice before purchase!!!
See:-
sound.westhost.com/fake/counterfeit-p3.htm
Sorry for such a long post, these Kenwood units of this vintage are well worth reconditioning and my aim is to assist in getting your unit going with minimum gamage to your wallet!!!
for the driver transistors, Sanken discontinued them, the replacements Sanken makes for them are 2SD2642 for the NPN, and 2SB1687 for the PNP.
since this is a design that ties the speaker line back to the drivers, most likely the driver transistors are also fried.
the 2SC4467 and 2SA1694 are listed in Sanken's 2010 catalog, so they are still currently in production. as mentioned above, order your transistors from a irreproachably reputable distributor like Farnell's, Newark, Digi-key or Mouser, i.e. distributors who supply parts to the large manufacturers as well as you and i. don't order them from e-slay, or some place that has a web site and a phone number, and not much else (they call themselves "brokers", i call them "phone booths"). companies like Farnells, Newark, Digi-key and Mouser are professional parts distributors, who monitor their product quality closely (they have to, their butts are on the line if they sell a large corporation like Boeing or Raytheon bogus parts)
since this is a design that ties the speaker line back to the drivers, most likely the driver transistors are also fried.
the 2SC4467 and 2SA1694 are listed in Sanken's 2010 catalog, so they are still currently in production. as mentioned above, order your transistors from a irreproachably reputable distributor like Farnell's, Newark, Digi-key or Mouser, i.e. distributors who supply parts to the large manufacturers as well as you and i. don't order them from e-slay, or some place that has a web site and a phone number, and not much else (they call themselves "brokers", i call them "phone booths"). companies like Farnells, Newark, Digi-key and Mouser are professional parts distributors, who monitor their product quality closely (they have to, their butts are on the line if they sell a large corporation like Boeing or Raytheon bogus parts)
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