Stuck on troubleshooting sub-amp plate - Page 1
Forum section: electronics / repair

author: kasumyku
author_rank: Regular Contributor
timestamp: October 21, 2017, 05:28:36 pm
content: Hello guys,I'm stuck on repairing a Boston Acoustics CS Sub10 subwoofer , pdf schematic attached.Symptom: Weak sound output even at high volume.A few years back I blew up the amp plate after cranking it up at a party.When powering it up the only thing I could hear was just a faint output. I took it to a repair shop and they fixed, but also set me back about $100.Last week happened again but this time at normal volume. Now I decided to try fix it myself...What I tried so far:-looked for obvious and found that when the technician fixed it, the only thing appeared to be resoldered/repaced was U203. So, I replaced U203(quad op-amp on pre-amp board, page 9 on pdf file) but with no improvement-pulled Q5 (D718) and Q6 (B668) on power amp board (pg. 3)- both tested OK-pulled Q21 (D669A) and Q22 (B649A) power transistors on power supply board (pg. 6) and found that Q21 had a voltage drop of 1.2-1.5v across Collecto-Emmiter on both ways.After replacing Q21 I've gained back volume but is still weak.It looks like the amp outputs only 1/4 of power (comparing when it worked fine)Any support would be much appreciated!Thank you!

author: Armadillo
author_rank: Super Contributor
timestamp: October 21, 2017, 06:38:38 pm
content: You should start measuring voltages like the power supply voltages instead of just changing components.Separate the pre-amplifying with the main amplifying to troubleshoot, that way you cut the circuit into half. Make life easier.Last page connector P03A, isolate pin 1 e.g. take out the capacitor one of the leg of C236. This is a suggestion to isolate the two.There are a lot of electrolytic coupling capacitors, any one of them can be the likely culprits.What measuring equipment do you have? If you don't have a oscilloscope, do you have a signal tracer?If both don't have, do you have PC or laptop external speaker amplifier. You can use it as a tracer.Hope it provides some insights to you.Edit: wild shot - temporary take out  Q10 [page 3] from the board, if no improvement, solder it back in in.

author: kasumyku
author_rank: Regular Contributor
timestamp: October 21, 2017, 09:24:58 pm
content: Thanks a lot for replying Armadillo.I do need some guidance on how to trace the signal as I am still a newbie...I got my hands on a scope not too long ago so I’m still learning how to take measurements.After separating pre-amp from the power amp do I start by applying at the LOW LEVEL(left and right) input a signal (like a 1Khz), then scope ground clip to chassis ground and use the probe before and after each op amp?Also, can I use my laptop or my iPod as a signal generator?What should I look for?1.Does the amplitude of the wave should increase after each op amp?2.What should the signal look like at the input and output of limiter MD1 with VR201(volume knob) at minimum and then at max?3.Do I look for distortion?Another question that I have might be a rhetorical oneCan I also use LFE input for my 1Khz signal or not because it’s a low freq input?

author: Armadillo
author_rank: Super Contributor
timestamp: October 21, 2017, 09:44:24 pm
content: It is good that you have a oscilloscope. You should repair yourself instead of paying us$100 the last time.Use the low level signal because the LFE bypassed a few of the modules, so it is not suitable to find the faults or do the repair.Apply low level signal from the usual source as you normally would [phono, cassette deck, radio etc], then put the oscilloscope at the Pin 1 of connector P03A. You should see larger signal than the input moving around. If you cannot see it, then the preamplifier is faulty. If you can see it, then the amplifier side is faulty which comprises, protection circuit, amplifier, mute circuit etc...Then you divide which ever faulty side by 2 again and continue to probe. Let me know which side and we can continue;But firstly as always, make sure power supply voltages are correct, speaker is not broken etc...Edit: Turn preamp volume control to mid level, use ac coupling, probe to 10:1, set say somewhere 200mv/Div, 1ms/div [adjust to suit].

author: Armadillo
author_rank: Super Contributor
timestamp: October 21, 2017, 10:01:50 pm
content: By the way, have you tried to remove the transistor Q10 to eliminate mute problem?Don't need to worry about distortion because you are troubleshooting loss of amplification problem now.The voltage at Pin 1 should be around ~ 1vac.

author: kasumyku
author_rank: Regular Contributor
timestamp: October 23, 2017, 09:39:03 pm
content: Hi Armadillo,I've tried to remove Q10 but no luck because its a small SMT transistor. BTW, most of the components are SMT except a hand full of caps and transistors...Power supply looks like like its in good shape . I've got the following readings from chassis ground to:+VCC +37.22Vdc-VCC -37.22VdcVB +27.25Vdc+15V +15.00Vdc-15V -14.91VdcOn the other hand the preamp board doesn't look so good. I removed one leg of C236 and used the scope ground clip on chassis ground and the probe on the leg of C236.As you can see in the pictures, my input is a 50Hz with a Vpp of 824mV and the output is 454Khz with Vpp of 432mV, please see pictures.Any idea how to go from here?Also, what +VCC, -VCC and VB stand for?Thank you!

author: Armadillo
author_rank: Super Contributor
timestamp: October 23, 2017, 10:35:13 pm
content: Hi, nice work there;The power supply voltages look good indeed.The VCC, VB, just take it as legends to identify the types of power supply voltages used for this particular amplifier, VCC, plus and minus supplied for the power amplifier, VB is used for protection and the regulated plus minus 15 used for those op-amp.Firstly, if you supplied 50 Hertz signal input, you cannot be getting 454khz output. So please tell me how did you inject in the signal and to what input port did you used.From your oscilloscope graphs, I can see that you are using DC coupling. Please switch oscilloscope to AC coupling input. Also please tell me did you calibrate the probe to 10:1 attenuation [there is a sliding switch on the probe and you also need to set the oscilloscope accordingly otherwise voltage will be read wrongly].454Khz is above human hearing ability, it may suggest that the circuit is self-oscillating but which I doubt so. Probe at location shown attached.

author: kasumyku
author_rank: Regular Contributor
timestamp: October 23, 2017, 11:39:31 pm
content: Thank you for the encouragement and support,For injecting the signal into the low level input I used my cell's headphones output.I'll be probing at the shown locations and post the updates with the readings.Probe and scope attenuation were set to 10X ; on the other hand coupling was indeed set to DC, great for pointing that out

author: Armadillo
author_rank: Super Contributor
timestamp: October 24, 2017, 12:14:55 am
content: Quote from: kasumyku on October 23, 2017, 11:39:31 pmSomething I need to point out is that, even you used DC oscilloscope coupling, because the pre-amplifier sections are mostly AC coupled by the coupling capacitors and the ops-amp is using balanced power supply, so we still should be seeing the waves somewhere in the centre of the ground / centre of scope. But it sat above the ground potential.So it suggested 3 things if the measurement is correct. One, the IC is faulty, two failure of the -15v supply, three, coupling capacitor faulty.But we know that -15v is ok. So please measure the ICs NJM2060 Pin 11 with respect to ground to eliminate this concern. it should read -15v. Check all the NJM2060.When all your oscilloscope measurement results are available, we can diagnose further.There are 2 anomalies that forbid further diagnosis, first the 454khz out and second, the above as described.

author: Armadillo
author_rank: Super Contributor
timestamp: October 24, 2017, 11:40:10 am
content: Also measure the voltage here;

author: kasumyku
author_rank: Regular Contributor
timestamp: October 24, 2017, 11:50:37 pm
content: Regarding the 454Khz....I realized that I pulled out the wrong capacitor leg, I desoldered on the side of the Limiter MD1 pin 3 and measured at pin 1 of P03A . That's why I was getting high freqAfter probing again it measured 50Hz 4.16VppI've attached a pic with rest of the readings.Also, all op-amps at pin 11 with respect to ground are reading around -15Vdc.Thanks!

author: kasumyku
author_rank: Regular Contributor
timestamp: October 24, 2017, 11:54:10 pm
content: I forgot to ask one thing...Why there's such a low reading at pin 1 of Limiter MD1 ?

author: Armadillo
author_rank: Super Contributor
timestamp: October 25, 2017, 06:04:39 am
content: Quote from: kasumyku on October 24, 2017, 11:54:10 pmYou should adjust VR201 left and measure, then right and measure to see the difference. The limiter will limit this signal regardless to max 200mvpp at In of limiter [if vccd is 15v and -vccd is -15V.[Edit: if so, output should not be over 4.166vpp you measured??, additional measurement points attached]You need to at least show me the scope trace at Pin 1 again [and the 380mv location]. This time use DC coupling, but first switch the oscilloscope to Ground and adjust to centre the trace then switch to DC coupling to measure the signal. I need to know if the trace is Centred or Loped to the side. [as those last measurements].Also you didn't measure the voltage requested. Can you measure it. We need to ensure that the mute is not "secretly" activated.I think the measurement looks Ok and we should we half completed [upon confirmation of the scope trace and the voltage].We can proceed to the amplifier side. Solder the leg of the capacitor back to the circuit [and adjust the vol control back to mid level].I will draw the amplifier side check location.I think you are mastering the amplifier circuit by now.Quote from: Armadillo on October 24, 2017, 11:40:10 amEdit: Additional Measurement Points attached to confirm output at 4.166vpp and check voltage of vccd plus and minus.Edit: Max Out = ~2.4 Vpp

author: kasumyku
author_rank: Regular Contributor
timestamp: October 26, 2017, 12:14:59 am
content: Hi armadillo,I'm kind of lost...As mentioned , I'm still learning how to use all the scope functions and what they mean...All evening I was on the net looking for info so I can make sense of your last directions.I understand that AC coupling means only AC signals will pass thru due to DC blocking capacitor but for DC and GND coupling I'm still scratching my head...I'll be watching some more videos regarding the AC/DC/GND Coupling so I can better grasp the idea and hopefully I'll get back to you with the measurements tomorrow after work.Thanks for your patience.

author: Armadillo
author_rank: Super Contributor
timestamp: October 26, 2017, 06:49:08 am
content: No worry. No rush;Suppose you want to measure a unknown signal. The actual signal is AC but with DC bias. How would it be represented in the scope.You can see that the AC signal is loped above the ground potential. So in another case if the bias voltage is very large, you wouldn't be able to see anything on the screen. That is the problem with large DC bias and small AC signal. That is also why I ask you to use AC coupling initially for troubleshooting because of unknowns.And so if I ask you what is the bias voltage in the AC signal and where is the Ground reference of the scope?So you would, to avoid stray voltage interfering, you would put the scope to Ground Coupling. Actually internally the input is shorted to Ground by the Scope so that the Ground Reference is shown on the Scope. You can also touch the probe to ground if you want do, but let the scope do it internally is better.The trace show the Ground potential and you can therefore calculate up from the grid to see what voltage the bias is and know where Ground potential is represented by the scope in the first trace above. You can adjust the ground reference by adjusting the vertical knob lower if you want but essentially it let you know where the ground reference is.Because your amplifier signal is complementary both positive and negative on ~ZERO ground bias, so the signal will be centred on the ground reference. In fact your amplifier do have a DC voltage protection to protect the speaker, that means if the bias is above ~zero, the relay will not engage the speaker.I did browse the rigol user manual and found short cut crappy explanation on this subject actually.

author: kasumyku
author_rank: Regular Contributor
timestamp: October 31, 2017, 11:58:51 pm
content: Much appreaciated for your explanation and directions.Hope I got this right...I know you have mentioned that at In of the limiter should be max 200mVpp, but with the volume knob VR201 turned to the left is 0Vpp and to the right is 1.62Vpp.Attached are the rest of the measurements with the volume knob turned 1/2 way.p.s.: I don't know if it matters or not but no speaker was connected during the measurements.

author: Armadillo
author_rank: Super Contributor
timestamp: November 01, 2017, 03:05:04 am
content: Quote from: kasumyku on October 31, 2017, 11:58:51 pmThe preamplifier including the limited appears to be functioning. Because the legend of the supply "VCCD" is not shown in the schematic, I have made the assumption that it was +/- 15V but instead you measured +/-36.0V. So the limiter should be functioning there at that voltage.So we should move on to the power amplifier section.But you need to hook onto the 100W speaker as load for the measurement to be done. Use jumper cables to the speaker if not long enough.Please measure the amplifier section voltages again. thanks.

author: kasumyku
author_rank: Regular Contributor
timestamp: November 02, 2017, 09:43:08 pm
content: Hi Armadillo,I have attached bellow the new measurements with load connected.And if its fine with you I will have a few questions after your input.Thanks!!!

author: Armadillo
author_rank: Super Contributor
timestamp: November 02, 2017, 10:37:42 pm
content: Quote from: kasumyku on November 02, 2017, 09:43:08 pmLong time ago in the beggining, I did say to remove Q10.... LOL. [how did I have suspected it?].Because the collector cannot be 0v and the base cannot be -ve voltage [measure again]. It appears that this transistor could be shorted. You have to remove it to check.The opamp output [voltage amplification] is too too LOW. It could be Q10 causing it.Replace these capacitors C01, C05, C06. [not expensive] or ESR it. Replace it is preferred.With Q10 taken out do new measurement as shown in attached.We need to confirm these before proceed any further.After Q10 is taken out, If voltage at output of opamp still so low, confirm Pin 8 voltage with respect to Pin 4 then change JRC4558D.Edit: BTW what were your question?Edit: If the amplifier power is restored, no need any measurement.

author: pamarakos
author_rank: Newbie
timestamp: November 06, 2017, 10:19:12 am
content: Hi to both of you and the restI've just registered for this threadThe only thing that I don't understand is how I got exactly the same failure at exactly the same date~!?~?~?~?!?!?I've given my CS10 with exactly the same behavior to a friend and he told me that he tested everything and it's the amp board, so I've googled d718 subwoofer and voila...here I am...so shall I get to a repair shop or shall I wait for your results to see what will come up? I don't have an oscilloscope but I do have some technical-electronic knowledge....Thanks a lotRegards to all

author: Armadillo
author_rank: Super Contributor
timestamp: November 06, 2017, 11:11:24 am
content: Quote from: pamarakos on November 06, 2017, 10:19:12 amWelcome!. You found the site.These days, modern electronics are built with self-destruct timers [MLCC timers] inside and yeah, it's no surprise they would likely fail just about the same time, though I am not certain if the CS10 fits the same category.But since your friend is repairing it for you, why the need to bring it to a shop?Our friend kasumyku did had a problem in removing the Q10 SMT transistor before, this type of device is quite small, so he may take some time to acquaint with SMT soldering and de-soldering. Yeah, first time always take just a little bid longer.Without proper tools, it may take a bit more time.But its a journey that everyone  will take, including me, once before.So it will be awhile.

author: pamarakos
author_rank: Newbie
timestamp: November 06, 2017, 01:31:28 pm
content: My friend just tested everything else, he tried to find some parts for the amp but he didn't manage it after all.So today I went and found a store that repairs amps and in general circuits, so maybe I'll have a luck. I wouldn't be able to de-solder such SMD with my equipment. I'll guess I'll have some news following days so I'll let you know. I hope till then we'll have some updates from kasumyku as well.Thanks for respondingC'ya

author: kasumyku
author_rank: Regular Contributor
timestamp: November 06, 2017, 02:25:07 pm
content: Hi Pamarakos,Whit the great help of Armadillo it looks like Q10 is shorted and few other caps are faulty.Yesterday I finally managed to remove it and I’m hoping tonite to post the new reading with Q10 out of the circuit.

author: pamarakos
author_rank: Newbie
timestamp: November 06, 2017, 02:31:29 pm
content: Q10 is this KTD1304?https://www.google.gr/search?client=firefox-b&dcr=0&biw=1920&bih=955&tbm=isch&sa=1&ei=4HAAWsOPPMiusAfsg77gDA&q=ktd1304+&oq=ktd1304+&gs_l=psy-ab.3...989.989.0.1125.0.0.0.0.0.0.0.0..0.0....0...1.1.64.psy-ab..0.0.0....0._kYpmf6NK9Q

author: kasumyku
author_rank: Regular Contributor
timestamp: November 07, 2017, 12:42:52 am
content: Hi Armadillo,After removing Q10 I'm getting all kind of weird readings, please see attachments.All its left now is to order C01, C05, C06 and U01.I'll post new measurement readings after swapping the parts.Thanks!

author: Armadillo
author_rank: Super Contributor
timestamp: November 07, 2017, 04:54:39 am
content: Quote from: kasumyku on November 07, 2017, 12:42:52 amHi;Firstly, as a double assurance, with the power off, please measure the ohms of the following resistors to confirm somewhere near to its value ; R02, R03, R04 and R05.Secondly, as a double assurance, measure ohm  across C02 which is 220pf, just to be sure its very high ohms and not short circuited.Those as silly steps but double assurance before you change the U01 which looks defective. With 50 Hertz input, I would expect output to be 28vpp and not 2.8vpp. [worth to double ensure that the probe attenuation is set correctly example 1:10? on the probe and on the scope setting.]Digital oscilloscope - for every measurement, if you cannot see any waves which you expected, then it is worth to press the "AUTO" or "AUTOSET" button on the oscilloscope because sometimes the "trigger" setting is not correct for the signal. I don't know if Rigol scope you are using label it as AUTO?. Do read the user manual about this.So after you changed the components [C01, C05, C06 and U01], definitely to a re-measurement and expect the output to be ~28vpp if the input is the same as before.No rush. Take your timeEdit: Forget to tell you, after you have replaced those components, remember to set signal source from zero volume up slowly before you blow the speaker. Your current input is overkilled. Do note!

author: kasumyku
author_rank: Regular Contributor
timestamp: November 07, 2017, 09:17:26 am
content: Quote from: pamarakos on November 06, 2017, 02:31:29 pmHi Pamarakos,Yes, that’s the Q10 which I removed but it looks there might also be other components faulty, like a few caps and U01 (please see Armadillo’s previous comment and my attachments with measurements)I’ll be posting updates after parts are replaced. Thanks

author: kasumyku
author_rank: Regular Contributor
timestamp: November 07, 2017, 10:44:25 pm
content: Quote from: Armadillo on November 07, 2017, 04:54:39 amThank you for the precaution regarding the input level!Regarding the measurements:-R02, R03, R04, R05 all read OK.-C02 measures around 25Kohms-I know you haven't mentioned for me to check but also C05, C06 measure around 25Kohms and C01 measures around 85kohms.-for the probe matching the scope attenuation, I think I had them right but just in case I have attached pics-regarding AUTO function: I try not use it most of the times but, in cases like this (when I don't see anything on the screen) I do use it. I appreciate the fact that you have pointed that out also.Now, regarding the parts:It seems that I cant find anyone selling this Q10 KTD1304 but Ebay and shipping from China is so slooooow.Would you know by any chance a CrossRef/alternative for Q10 or some other online sellers( I've tried Digikey, Mouser and Newark and no luck) ?Here are the rest of the parts that I'm about to order:For U01https://ca.mouser.com/ProductDetail/NJR/NJM4558M-TE1/?qs=sGAEpiMZZMtCHixnSjNA6NG6IBDWSupwerxZzjC5lQk=For C05 and C06https://ca.mouser.com/ProductDetail/Panasonic/EEE-FK1C220R/?qs=%2fha2pyFadugyxpIbZVcwfvp4YAOdsJG%2fwGkS7w0%2f1WHn2b1efBuOcA==For C01https://ca.mouser.com/ProductDetail/Panasonic/EEE-FK1C100R/?qs=qE6bgDGEOCvwL%2FHBRL1emg%3D%3D

author: Armadillo
author_rank: Super Contributor
timestamp: November 08, 2017, 12:24:20 am
content: Quote from: kasumyku on November 07, 2017, 10:44:25 pmThere is a direct replacement from ebay for KTD1304. This is not a critical part to operate your amplifier, so you should be able to wait a bit longer for it through the mail while you enjoy the boom.Since your circuit is using rectified mute signal from the preamplifier, you can try BC817, BC818, KSC326.Alternatively, confirm that the dismantled KTD1304 is not faulty by measuring it with a transistor tester or multimeter [watch youtube how this can be done].

author: Armadillo
author_rank: Super Contributor
timestamp: November 08, 2017, 04:19:47 am
content: Regarding your previous measurement that the base of the KT1304 read -ve voltage, I was thinking of visiting it later after your amplifier is repaired but since you are going to buy the transistor, so you should also verify the Diode D200 [see attached] using multimeter on Diode Mode to check it, one side conduct and one side don't.1N4148 let's hope it didn't turn into a resistor [both side conduct at some ohms].

author: kasumyku
author_rank: Regular Contributor
timestamp: November 10, 2017, 01:11:09 pm
content: Hi Armadillo,Transistor Q10 has been damaged in the process of removing it from the board so no chance of testing itRegarding diode D200, it tested OK.I'll be posting updates after getting the parts in.Thank you again for your time, patience and support!!!

author: kasumyku
author_rank: Regular Contributor
timestamp: November 15, 2017, 12:54:33 am
content: Armadillo, it works!!!!!!!A million of thanks wouldn’t be enough to show you my appreciation !!!I think it works better than when it was new, because it hits such low frequencies now that I haven’t heard before.As I mentioned, I have a ton of questions for you but I’ll limit to just a few:1. Why is not a gradual increase of signal when tracing it through the preamp board, from the low level input up to the last opamp’s output. I mean why the signal amplitude is up and down at outputs of the op amps(or even no readings at the input of the first couple of opamps). Shouldn’t the signal increase after each op amp?2. How did you know or what made you think that the caps were bad( BTW, all were indeed bad)3. What are some good books regarding audio amplifiers on how every stage works or how it should behave and also the most important thing how to troubleshoot in the same way you have guided/shown me.I hope you understood my questions as you can see that english is not my 1st languageThank you!!!

author: Armadillo
author_rank: Super Contributor
timestamp: November 15, 2017, 05:09:34 am
content: Congratulation!I am happy for you. Well done!Quote from: kasumyku on November 15, 2017, 12:54:33 amBecause some of the sections/stages are actually frequency bandpass filters, in this case specifically low frequency filter and they do loss/attenuate the power through it, some are buffers or amplifiers to cater for the designed losses through the sections.Quote from: kasumyku on November 15, 2017, 12:54:33 amIn electronics, there are the small signal and the large signal to deal with. Electrolytic/MLCC capacitors age through time especially with larger signal it handles at that section. Further more, this amplifier is for low frequency amplification, hence it needs larger capacitor to pass the low frequency signal across in fidelity. Hence it is appropriate to change it especially since the symptom is loss of amplification.Quote from: kasumyku on November 15, 2017, 12:54:33 amAs you continue your journey in electronics, the troubleshooting skill will come with it, and gained through time and your exposures. Judging by your interest in electronics, I am sure one day you can be the better expert in it. Let me flip through the notes and will drop you a note on the book on amplifiers.Cheers;Regards;Armadillo

author: pamarakos
author_rank: Newbie
timestamp: November 15, 2017, 07:52:24 am
content: Quote from: kasumyku on November 15, 2017, 12:54:33 amSorry for getting into the party:) So I ve read all of it from the beginning but to be perfectly sure, problem was all the capacitors on the amp board? This is what you ve changed and now it works?Can you please tell me their "codes" on the diagram like for example c01 etc?Sorry for losing some more time of yours...Thanks a lot

author: pamarakos
author_rank: Newbie
timestamp: November 15, 2017, 07:56:59 am
content: Quote from: Armadillo on November 15, 2017, 05:09:34 amSo it was all the caps after all?Just in case kasumyku doesn't respond today, can you please confirm?Sorry for bothering:)Thanks again for all your knowledge shared.

author: kasumyku
author_rank: Regular Contributor
timestamp: November 15, 2017, 10:27:53 am
content: Hi Pamarakos,No worries, here are the components I have replaced:U01 (njm4558m)C01, C05 and C06Q10 ( diagram asking for ktd1304 but I have used ksc2365)Also check Q21 and Q22( part of power supply)Thanks.

author: pamarakos
author_rank: Newbie
timestamp: January 09, 2018, 12:02:23 pm
content: Hi ArmadilloI ve got mine returned repaired, he said that he replaced two transistors, didn't say which, everything is working ok as it seems now, except I can't remember if crossover was working when used lfe input or only on l/r input. Because now it works like this.Have you got any idea? Already asked kasumyku too, if you've got any idea please let me know the soonest so as to return it if it's not supposed to work this way.Thabks a lot

author: Armadillo
author_rank: Super Contributor
timestamp: January 09, 2018, 12:31:07 pm
content: Hi, nice to hear that you got your unit resolved.For your question, is best for kasumyku to reply you. But I try;As far as I can tell, lfe input is for low frequency input if your device has already a crossover unit that separates the signal and provides the lfe [low frequency] signal to this sub-amplifier.if you don't have any device that provide lfe output;then you can connect the audio signal to the l/r input, because internally it contained low frequency filters to only filters low frequency for the amplifier to amplify.All this connection details can be found in the user manual.If you are already using the l/r input and is satisfied with it, then you should be safe.I trust kasumyku can provide you with better explanation.By the way, 2 transistors should be cheap for you to send it out for repair? How much it cost you? I think you friend should be reasonable.

author: pamarakos
author_rank: Newbie
timestamp: January 09, 2018, 02:08:02 pm
content: I ve used lfe always before as my amp shows lfe sign at his preout sub output. Also when lfe is connected sub plays louder than r/l channel.Let s see what kasumyku will say. Thanks for your response.

author: kasumyku
author_rank: Regular Contributor
timestamp: January 10, 2018, 08:36:24 pm
content: I don't know if i'm right but looking at the schematic it does look like the cross over pot is only wired for the L/R input and doesn't make any sense because mine does work regardless of the input , but as you can see I'm still at the very very beginning of my troubleshooting journey and to be honest, I'd probably would had very slim chances or none of fixing it on my own if Armadillo wouldn't guide me thru..

author: pamarakos
author_rank: Newbie
timestamp: January 10, 2018, 09:28:45 pm
content: Funny thing is that I do remember very well that I used this crossover knob to adjust the bass every time together with the volume. I can't remember it wrong. I don't know what to say, I ll filter it from my main amp and never take it back to the repair guy:)