Servicing a 1977 Kenwood KA-7100 Integrated amplifier - No Sound. No relay click

[@minilab9030]

Rapid diagnosis of transistor failure is more difficult than diagnosing radial/axial electrolytic capacitor failure. A joy to watch. Thanks Jordan!

[@gichti1971]

Who tf gives a thumbs down on such an excellent troubleshooting and repair video?

[@ernestmccollum2397]

Easy answer. People against right to repair. Want you to spend money buying new equipment.

[@zulumax1]

Had the same issue with my Sansui AU-7700 that I still have in my collection. It would take longer and longer before the relay would click on, until one day it would click no more. 35 years ago I replaced the relay and 3 caps in that circuit, and it is still working today.

[@helicopterske2]

Wonderful tutorial! My KA 7100 that I bought new in high school is now up and running again. It was the transistor. Thanks for posting this.

[@pubsub9832]

I absolutely love watching your repair videos sir. You brilliantly convey a wealth of information and you are great at technical speak on the fly. Keep it up!

[@Android_Warrior]

He fixed my cassette deck and still going strong, thanks JD!!!!

[@taijkon]

I´m hording these old Kenwood amps :) I just love them. Thanks for all info and a very interesting video.

[@Synthematix]

Im not gonna lie, you sir are the master of amplifiers

[@KillerKlipsch]

You Rock!!! I did exactly what you said and now I have an amazing sounding Kenwood. Truly appreciate your talent, thanks so much.

[@JohnThomas-gl4qu]

I enjoyed that. I liked the way you went through in detail the locations and values of each capacitor and resistor and showed the test values on the multi-meter. Gives me confidence I can do this myself.

[@andymouse]

Very informative and great vid, now all I need is a KA-7100 !.....cheers.

[@md_sc5855]

I've got a KA-701 looks like a sister unit, was looking for how to clean the switches, this is perfect! And I learned a bettermethod to use solder wick: I've only been contacting the end, you hit it with the side! I'll try that! Excellent resource! Thank you!

[@lawrencedavidson6195]

Very nice helpful video. Thanks very much and greetings from sunny Jamaica. (Waiting on the storm Elsa)

[@zx8401ztv]

Smashing repair jordan, the owner will/was happy as a sand piper :-D I have also used larger transistors with a bit more gain, the Tip41A is handy for medium power regulation/switching and similar. The BC337/327 handy for general use, The 2N3055 or 2N3772 for d.c supplys. It's supprising what you can get away with when an obscure part can't be found.

[@justsumguy2u]

Your amp/receiver troubleshooting vids have always been my favorite. Very interesting about the driver transistor being weak, but not open---maybe lesser techs would've been tripped up by that

[@valerianpantsulia5137]

Good video and cool explanation

[@quantumleap359]

Good video Jordan, thank you.

[@randyc8171]

I had for almost 40 years a 1981 Kenwood KR something 40 watt per channel receiver/amp. It operated extremely HOT. In later years I had to put a little fan on it in an attempt to cool it when operating. I was told that was normal for that vintage of Kenwood receiver/amps.

[@LeoRousseau]

You sir are very smart! I have the KA-7100 and the only thing that I'm getting out of it is the relay click. On the right corner of the board is R76 and I have the feeling that it might be cooked, but I will be honest with you and just say that I have no idea what I'm doing. I received this from someone last week and he just said that it doesn't work. So I opened it up, plugged it in and when I flipped the power switch I got the relay click in about two seconds and saw a tiny bit of smoke around the right hand side of the board but by the time I got my light on it had cleared and just a little smell was left.

[@rccarloverluxembourg718]

so glad I have thd 7100 and not the 6500, would be cool to have the KT-1100 sd and thd KT-1100 and the Revox Tuner, all just giving no music. Thanks for giving me good vibes if my 7100 gets a problem.

[@Justplast]

Jordan A1 Job mate. From OZ

[@dankolov1839]

Thanks to the master for the review of this amplifier. I have such an amplifier, which I gave to the repairman for analysis. He told me that he replaced the capacitors that were replaced. But that's not all........ 4 pcs. He did not replace the large capacitors either. He said that this was not necessary and they were within their parameters. He told me that all the capacitors on the signal paths in the power amplifier were replaced. I see that he did not replace some capacitors in the preamplifier boards. more, that he gave him a full set of capacitors that he bought on ebay for this amplifier. Of course, he returned the rest of the capacitors to me. The amplifier works without a problem after the repair. But it worries me that he did not replace four large capacitors. He gave it to him Nichikon KW ( M) 6800uf 63v. He did not replace them and returned them to me. I ask her why and did he do his work. Well, of course it is possible and he did, but after this partial repair, how long can this amplifier work without replacing the main large capacitors, although they are 45 let. And I use this amplifier constantly, maybe 10 hours a day. And every day.

[@VicariousAdventurer]

I looked at a video of somebody replacing big electrolytics in a Sansui. He measured them at 2/3 rated values, even though the amp worked. There is no way that the caps were not aged and much smaller capacity than listed.

[@PhuckHue2]

Wow its so clean for being 45 years old

[@Jason-zh7wo]

Nice job 😀👍

[@JamesE707]

Your relay story has just reminded me that very recently I ruined a cheapish pair of headphones when I switched off the power to the amplifier. So what was happening? - well, someone (in their wisdom) had bi-passed the voltage dropping 330 ohm resistors (for the headphones) making an effective resistance of less than 3 (three) ohms! Later of course I rectified the problem, but the 'popping' of the headphones was a consequence of not having protection circuits in place. Sure, if the original circuit was left alone, this would not have happened. BUT that's what we can expect when we buy stuff second hand!

[@noonyouknow]

Dude! I can't wait to get to my KA7100 that I bought while in the Army! If I can't get it back up and running... I'm going to ship it to YOU! HAHA.

[@richardbrobeck2384]

Yes I work on many kenwood units over the years

[@HealthFitnessMartialArtsDEng]

Hi Jordan. Mahalo for this excellent tutorial. I'll go over with my stereo tech what you've done. However, I've noticed something peculiar. When the amp was first turned on, the relay went on. After a minute, I turned it off. Turned it back on and voila, no click. Upon playing with the knobs and switches, the relay would click when I turned the attenuator up to -53db. Turn it back down the relay opens. The other idiosyncrasy is that with the attenuator at -90 (no volume), with the tone control switch turned on, the relay would click on! Turn off the tone control, the relay clicks off (open). But after about 5 min, the relay will start to click on and off and eventually stay open. It's a similar situation with the sub sonic switch as well. But the relay stayed on (closed) after 5 minutes. With both tone control and sub sonic on, the relay will eventually turn off. With the switches on, I'll turn the attenuator up to -54 db. I can then turn off the sub sonic and tone control switches and the relay is still on! Bizarre behavior. What's your take? I hope to hear from you soon. Mahalo for your time and thoughts. Footnote: I had already changed out C40 because whomever worked on this amp prior, put the cap in reverse polarity so it was getting puffy. The speaker relay had also been change out prior as well with the the one you showed at the end of your video.

[@JordanPier]

Very strange. I would check that all grounds to various parts of the machine are intact, sounds like a loose ground. Could also be bad solder based on thermal cycling and vibration. Without having it here its only speculation.

[@HealthFitnessMartialArtsDEng]

@@JordanPier hi. Mahalo for responding. It was interesting getting that trickle of power from the control board to the amp board. We were going to put in a 10uf cap on the blue and yellow wire to act as a filter. But I suggested we check out the regulated power supply as you had. Low and behold, there was indeed a bad solder joints at the series pass resistor Q31 on the leg that should have shown 28.5v. Now all worked well. However, I let it run for a bit last night, simply plugged in, nothing connected. It took about 10 min and the speaker relay clicked off/on! It would do that randomly, no pattern. I would turn the unit off for a bit and then on again for bit. And at random moments, the relay would click off/on. After about 2 hours of this, the relay finally stopped clicking on. So I'm surmising either c41 or c39 may have died in the protection circuit. I don't have a cap checker so I'll have to take it back to the shop to check c41 and c39. I don't think the Q34 driver transistor is bad as the charge up at the speaker relay is fast and does not draw down. If you ever work on a Yamaha CA410II, Optonica SA5901/5905, Technics SA1010, I would love to see that!

[@JordanPier]

@@HealthFitnessMartialArtsDEng the capacitors could be failing but that usually means a long time between power on and when relay engages. Thr driver transistors for the relay are suspect as they will loose their beta (gains) and become weak to the point they wont drive the relay coil. A transistor checker or component identifier may confirm

[@HealthFitnessMartialArtsDEng]

@@JordanPier Capacitors are good. Did you say a replacement driver would be a 2SD 438? I can't find that at Digikey. The closest I found and it's obsolete is the 2SD2438 and I am not sure what to look for similar. Moving along to the Toshiba 2sc4614s which is also obsolete, in the marketplace, there are about 46k and that part# 2SC4614T. Now if I want to stick closer to the original 2SC1213, it looks like the marketplace has about 1200 available part# 2SC1213AB. I take it either of these 2 will be a suitable substitute? Mahalo again for your time and help.

[@JordanPier]

@@HealthFitnessMartialArtsDEng in theory they would work. Usually the suffix stands for some revision change: a higher beta (gain) or slightly higher voltage. You'd need to compare datasheets to be sure. However given the simplicity of the circuit i think the substitutes would be sufficient

[@lenoradiane5474]

I enjoyed your video very much. The only thing I wished was a little clearer was when you were checking DC offsets, I'd have liked to see how you connected your scope. Thanks again.

[@JordanPier]

I have the scope connected across my test load and set the coupling on the scope to DC instead of AC

[@dkubarek1]

This video is great. Really easy to follow and I learned a lot. I have the KA-6100 and it sounds pretty good. I assume it's similar and I should look for the same problems? Also, you don't seem to aimlessly recap everything, which is great because that's how I break things. Would you not worry too much about the phono stage and aux? They're kinda hard to get to on my model.

[@pancho1071]

I got this same unit.looks great sounds amazing.just can't beat those fully all round metal aluminum face and knobs.unlike today's plastic crap.

[@iantyler4045]

ESR meters. Worth their weight in gold.

[@josephsirois2353]

Nice job JP , but you keep teaching everyone an us techs we be out of a job 😆

[@md_sc5855]

i opened up KA-701 and your lube process worked great... i wish i could post photo, i noticed i have one of large PCB traces (right along back of board) has obviously overheated, coating is gone, copper shows , and that shield for RCA jacks got hot close to that damage too! And some of solders in that area now have "cooked" rosin showing around the solder joints! Do i re-solder the joints? and do you put a jumper around damaged section of trace? maybe to a component pad on each side of damage? Appreciate advice...

[@fedsweet1234]

NEW HERE LIKE IT THANK YOU

[@paulharbin2510]

Jordon I have the exact same issue but after changing C39, 40 and 41 the relay coil voltage changes even slower than the one in your video. Pulling Q34 and testing it shows a gain of 166. What is the problem?

[@jackjohnson3684]

Dam this amp looks so clean mine is getting rust

[@dkubarek1]

What desoldering wick do you use? I need to get it so I can know it's all my bad technique 🙂

[@TheC5corvette]

Im a newb to all this but have adjusted bias current before... But i have one of these amps and it seems not up to potential and decided to give more cleaning and check bias current... Ive double checked my work but my unit was reading very low bias (aprox 5 mv) on both channels) Does this mean unit may have other trouble somewhere else or should i just get it near 20mv which i just did. .I also let it sit turned on for awhile, and volume is 0 and balance is center

[@jeffreyhaynes5774]

May be you can find a B&K 520B semiconductor tester on ebay,i still have mine and still working.Tested many transistors,never let me down.

[@nolanboyle8087]

Great video! Im very new to electronics repair and trying to learn. Following your video I confirmed that the relay in my stereo (luxman lv103) is not engaging. I tested the voltage on the output resistors and found the left channel has 51 volts. Right channel has 0 volts. There are six led lights on my board (im assuming these are to help diagnose a short). One of the six is not illuminated on the left channel section of the board. Clearly something is wrong in the left channel and it is causing the relay to not engage. What would cause a voltage in the output residtor? What is the next step?

[@JordanPier]

First I would check if output and driver transistors are shorted. Then look at class a section and differential amplifier.

[@vintageav]

Great content, thank you! In this video you mention a condition where there is a buzzing sound even when the volume is set at minimum. Can you expound about what can cause that? Thank you!

[@JordanPier]

Defective capacitors in the power supply will cause this. Find the asymmetry. The bad side will have a lower voltage and have measurable ac voltage from ripple caused by the bad caps.

[@71Fenderv22]

Thank you.

[@kgsalvage6306]

Hi Jordan, Which solder wick do you like the best?

[@JordanPier]

Chem-wik #4 .100"

[@JamesE707]

Without a circuit diagram, repair jobs would be generally much more tiring and time consuming. The KA-7100 looks like a decent amplifier!

[@tomsettles6873]

Jordan - I have both Kenwood KA-5500 amp and Kenwood KA-7100 amp. I had a nice 8100 amp before them. All are in pristine condition and I tested all capacitors in both, did visuals of all resistors, etc. and everything is good on all 3 amps. I'm finding that the 5500 sounds better than the 7100 and 8100, especially in midrange. The 5500 has way more clarity in the mids and highs. Because the 5500 doesn't have a Loudness button, is it possible the Kenwood engineers cranked up the mids in the 5500 to make up for the lack of Loudness button?

[@JordanPier]

Every machine has a different flavor and sound based on what value point people wanted. I don't know what specific things are done to make units sound unique.

[@zari63]

@@JordanPier great video sir

[@rogertyler3237]

Do those Toshiba 2se 246 14's Go in A Certain Way? Or Not?

[@JordanPier]

Yes, orientation matters. You just have to know what leads are what. Base, collector, emitter.

[@firstlast4637]

I have the same unit and the right channel plays lower than left channel. I swapped the speakers and the same result. Any help would be appreciated. Thank you!

[@JordanPier]

Flip mono switch on. If channels equalize clean input selector and tape monitor switches. If not, you've got preamp or power amp issues. Too many possibilities at that point

[@dxjxrose]

So now that the 2sc 4614 is gone what do you recommend

[@JordanPier]

www.digikey.com/en/products/detail/onsemi/2SC4614T-AN/2797026 Get em while you can!

[@jugent2012]

Have a question for you and has nothing to do with the kenwood,,,,,where can I get good belts for a nakamichi bx-100, hope to hear from you, Thanks

[@JordanPier]

Wish I knew. Still looking for a good source....

[@jugent2012]

@@JordanPier well when you find it let me know if that's okay. Thanks.

[@Al-mu4ff]

Do you have a business website for repair work? I have a KT-5500 that is inoperable.

[@JordanPier]

Repairaudio.com

[@vonleyser]

Amazing, been carrying mine around for over 45 years, would like to send it to you to fix my volume issue and give it your blessing with what you think it may need to last me another ? seven years & I'll be happy. Sent you an email to see if you have time for another job.

[@JordanPier]

Didnt get it.. what address did you send to?

[@vonleyser]

@@JordanPier I see my mistake, resending

[@JordanPier]

@@vonleyser got it. Will respond as there is time!

[@08ahoward]

Jordan I have a sansui qrx 3000 that has distorted and weak channels. Any input on what maybe causing this? Thanks

[@JordanPier]

Too many causes. First try cleaning the switches and controls with a good known contact cleaner like CRC or deoxit F5. If it still persists then you need to do some component level troubleshooting, discover the section causing the issue and resolve it.

[@08ahoward]

@@JordanPier thanks man

[@08ahoward]

Is it normal for the r78 and r77 to become hot to touch?

[@JordanPier]

@@08ahoward don't know. Have to observe resistor value, wattage rating and use in circuit. Resistors can run hot enough to melt your skin, but if they're smoking you have issues

[@08ahoward]

@@JordanPier thanks Jordan you da man

[@RealHIFIHelp]

Tricky stuff.

[@Synthematix]

I want a capacitor wizard!

[@dirkk792]

Jordan; Please clean your Oscilloscope !!! Its so dirty !

[@shriraamsugavanam1870]

Dear sir how are you? Iam servicing a Philips DVP3618 DVD player. The complaint is it had played most of original DVD CDs which were brought from the Amazon. The CD S doesn't have any scratches or and damages. The DVD player is able to play VCD CD but now it is not playing DVD CD s anymore. It recognises the CD and coming upto to choose language or play movie option. When i click the play movie it stops. The same CD is working fine with Sony DVD player. It is bit tricky because the Philips DVD is playing some CD like VCD ones and other duplicate copy CD but not playing original DVD movie cd. Please suggest me which part should be replaced or defective. I've tried DVD cleaner CD but no significant improvement. This player played all the original DVD CDs years before but now it is failing to do. I am expecting your kind reply sir. Thankyou.

[@JordanPier]

Laser pickup is aging to the point where heavier data density discs will not be readable. Consult your service manual for laser head part number if not on the laser itself. You may also have only the replacement disc drive as a whole as an option

[@shriraamsugavanam1870]

@@JordanPier Thankyou sir. I will try to find the new mechanism. Thankyou so much sir.

[@rogertyler3237]

What Do You Think Of These Older Folks Working On Those Old Tube Stereo Receivers?

[@JordanPier]

Don't see anything wrong with it as long as you know what you're doing. I learned from older gents who had been in the industry a long time. Experience conveyed is far better than any class or text book

[@zari63]

Can you please tell me the spec of your resistor load that you connect your scope

[@JordanPier]

8 ohm 250 watt wire wound resistors

[@zari63]

I have metal one (Golden colour) u prefer wound wire?? @@JordanPier

[@JordanPier]

@@zari63 wire wound mimics speaker voice coil. Inductive properties are similar

[@shriraamsugavanam1870]

Dear sir, i am recently servicing a Philips cassette tape recorder it has an output stage defect. For the replacement i have bought 2SD72 and ECG103A NPN transistors. To test the Sanyo 2SD72, i had set the multimeter knob to the diode testing position. The base to collector and base to emitter got forward biased. Reversing the above mentioned, it got reverse biased. Then i checked the collector and emitter. There was a forward biasing reading found between the collector to emitter and reverse bias between emitter to collector. It was little iffy. Then i checked the ECG103A (2 Nos) where again i found that collector to emitter showing reading in 250 or above values. I thought both of them should be leaky. Shockingly the AC127 transistor also became leaky like the above. After that i tested the AC128 (10 Nos) & 2SB405 (3 Nos) PNP transistors where there was no leakage readings found between the collector to emitter and emitter to collector. Both the leads got reverse biased in both type of PNP transistors. The NPN transistors becoming suspicious in this case and PNP is good. When i connect them in a complementary symmetry circuit, it amplifies well and no distortion occurred. But even at zero volume level, i was able to hear a hum or noise like when we touch the amplifier's audio input terminal with finger we may hear a hum. That kind of hum came but no transistor over heating occurred. I am not able to remove that hum anyway. I replaced them with silicon pairs BD137 & BD139. That time there was no hum but huge distortion occurred. I know that we can't simply replace the Ge with Si. Please suggest me and clarify whether those Ge NPN transistors are leaky or not. Do all the NPN transistors have collector to emitter leakage? I am not sure about that. I am expecting your kind reply sir. Thankyou.

[@JordanPier]

You are experiencing something normal. The older germanium transistors are leaky and as a result require less forward voltage to bias. Using the newer silicon defines requires more forward voltage to turn on which is why you're experiencing the distortion Hum and noise is common of early germanium transistor designs.

[@shriraamsugavanam1870]

@@JordanPier Thankyou very much sir. Fortunately I have found a schematic of complementary symmetry amplifier using TIP31A &TIP32A. I can use it instead of leaky germanium transistors. I am using BPL ECN 9003 1989 PAL system colour tv. I have replaced the entire tv board in 2001 due to lack of channels and most of components gone bad. Now the tv is still working, the picture, raster, sound everything is ok. But the problem is little eccentric which is when I start the tv and watching, the picture appears normal but a waving lines appears like 'S' form. That lines are moving up and down like waveforms. It is not retrace lines or grains or picture rolling. I am using my DVD or set top box only. After 10 minutes the waving lines diminishes and the picture becomes as usual normal. However the waving lines present and clearly visible in the bright scenes. In the Dark scenes that waving lines were not visible. I have tried in the way by adjusting the brightness and focus in LOT, changing the big capacitors ( don't have ESR meter to confirm) and checked the diodes and resistors and poor soldering joints. But i am not able to predict the defective part or components. Please suggest me which part should i have to check inorder to mitigate the waving lines problem. You have brought many older television receivers back to life. That's really cool. Your guidance is very helpful. Please give your kind reply sir. Thankyou.

[@JordanPier]

@@shriraamsugavanam1870 waving picture is usually due to bad filter capacitors or bad rectifier. Could also be an open ground on the B+ line

[@shriraamsugavanam1870]

@@JordanPier Thank you so much sir. I will check the B+ line and replace suspicious capacitors. I would like to buy an ESR meter. Which is the best one please recommend from your side sir. Thankyou.

[@JordanPier]

@@shriraamsugavanam1870 www.amazon.com/dp/B00O0BN3H2/ref=cm_sw_r_cp_apa_glt_fabc_YZEVTZV9J0N83QV68SR0

[@lewiskhan9825]

grate stuff! do you think this model is a keeper ?

[@JordanPier]

Yes, it's one of their better offerings.

[@Synthematix]

@@JordanPier Their TRIO brand was better

[@charleslauter5035]

If the amplifiers are high quality they should be tested for distortion not just nice looking sin wave. ( harmonic - intermodulation )

[@daniel_cardenas]

Limpia el osciloscopio.

[@michaelgalilaer7209]

I have the same problem with an Arcam A-18 it starts to clack or the car stops and the problem also occurs with mechanical pressure as in the video. kzbin.info/www/bejne/hqTNaZWoncaGq7s