ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
As I was suspicious of the muting circuit, I started there, checking with the table from the manual, and what do I find there, D12 is missing, I never did anything in that part, nearest was changing C14, I will put that one in and lets see what happens.
Collecting Vintage B&O is not a hobby, its a lifestyle.
Søren Mexico: As I was suspicious of the muting circuit, I started there, checking with the table from the manual, and what do I find there, D12 is missing, I never did anything in that part, nearest was changing C14, I will put that one in and lets see what happens.
Not missing, sitting on the solder side
good - you have it working
The Dickster: good - you have it working
Barely, no volume.
Was checking this and I have these results, as I dont know the uV on the antanna, its measured with no antenna connected.
Did you mean to put -12.2V as your measured TP14 value?
If not, and if I read that chart correct, it would seem like your muting is always on with a +12.2V at TP14.
sonavor: Did you mean to put -12.2V as your measured TP14 value? If not, and if I read that chart correct, it would seem like your muting is always on with a +12.2V at TP14.
!2.2V = -12.2V
Okay, so with the muting circuit apparantly fine, I think the next thing you could check that doesn't require taking anything apart is to route the tape record signals (tape 1, then tape 2) to another amplifier and see that it plays okay. That won't verify your BM 4400 pre-amp circuit but in routing the 4400 FM signal (as well as the other inputs) it would eliminate that they have a problem. It wouldn't seem like they would be part of your problem but it is something non-invasive you could try. Otherwise you may have to dig back into preamplifier and power amplifier circuits...although it is still odd that both L & R are affected equally by this problem.
I will go back to it in a couple of days, have some jobs to do next week, glad you are helping John.
I wish I had better answers but eventually the solution will come. If it takes me comparing signals in my BM 4400 we can do that. As I said earlier, I have Frede's Audio Tester project on my bench right now. I think I am about 25% into that project right now. If we don't have the solution figured out on your BM 4400 when I finish the tester then I will move my 4400 to the bench.
In September you mentioned that all trimmers on the audio connector board 4 where set to zero.
Maybe the previous owner / technician had the same problem like you, everything to low soundwise.
I would try what member sonavor mentioned yesterday : Inject some constant tone around 1 or 2 kHz into the tape 1 or 2 input, set audio switches to linear and loudness off, tone control to '0', Steroe/ Mono switch to Stereo and try to measure the AC Voltage you injected into TAPE 1( or2) through the pre amplifier circuit. Start at P17-9 for the left channel
You don't need a real oscilloscope for this failure finding. Try the for private use free program here:http://www.zeitnitz.de/Christian/scope_en?mid=4.01 (The author is not me) The program gives the possibility to create a test tone with the build in sound generator (available via the line-out of the soundcard and can display the 'received' signal from line-in or microphone input of the soundcard. This way you can see where the signal gets lost or lowered, where it shouldn't be.
This software can be used for voltage levels of usually +/- 0,7 Volt that is enough for preamplifiers. If the voltage is higher a voltage divide is needed).
Ralph-Marcus
Thanks Ramabo, I will get into that as soon as I get the time, has some jobs to finish up this week,
As you saw, your latest help was a big step forward, my knowledge is, as you have seen, limited, so I'm grateful for any help available.
Will get into it asap.
Thanks a lot Søren
Forgot to mention, running FM gives the same sound level as a CD through Tape 1, the trimmers for level adjust on the PCB 4 are all set to mid level.
Connecting the tonegenerator to Tape1, with 2Khz I get at P17/20 pin 1, 0.4VAC stable, going through the test points until TP 207 I get Same values DC right and left, at TP 1/207 1.6 VDC, where do I go from here.
Back tomorrow.
What voltage level does your 2K Hz test signal start out with at TP102? Can you check the 2K Hz AC level again at TP120 and TP107 for different volume settings? Any DC voltage at TP107 and TP207 will be blocked by capacitors C132 and C232 from entering the power amp section.
When I use my DMM, I have - (black lead) to chassis and + to the pin 1, P17 I can switch my DMM to AC and get the 0.4 V when I measure further in on the test points on AC I get only very small fluctuating readings, switchng to DC, I get the, at the test point, written readings.
Am I measuring in a wrong way.
Søren Mexico: When I use my DMM, I have - (black lead) to chassis and + to the pin 1, P17 I can switch my DMM to AC and get the 0.4 V when I measure further in on the test points on AC I get only very small fluctuating readings, switchng to DC, I get the, at the test point, written readings. Am I measuring in a wrong way.
I don't think so but the DC measurements verify the biasing voltages. The test signal (2K HZ AC...at some voltage you set at the generator) represents fixed frequency audio tone going through the amp. So your DMM should hopefully be able to measure its level (and frequency) at the input (Tape 1 IN) and again at TP107 where it has gone through the pre-amp volume control. You should be able to observe the volume control affecting that test signal (AC). What level do you apply at the input? You said you measure 0.4 V. Do you measure that with your DMM right out of the signal generator?
I measure 0.4 VAC at P17-9
Søren Mexico: I measure 0.4 VAC at P17-9
Okay, P17-9 is at the start....prior to the volume control. What is it at P17-1 or TP107 (after applying volume)?
John I downloaded a software mentioned earlier in the thread, I found out how to use the signal generator, and could apply a 2Khz signal, the signal will be up to 0.7 VAC, I think depending on the computer.
I will try to get time tomorrow, today was a little stressed and short of time. Will be back tomorrow
John and Soren,
Even if the DMM is only capable of measuring up to let's say 500 Hz the correct value, it doesn't matter as long as one get a somewhat senseful reading. So 0.4 V AC at the input of the amplifier is a good working base because one can see the effect of the balance and volume potentiometers well
The whole thing is a quantitative measuring to get the fault in this machine not a qualtitive.
As John said all pots set to 0 (except volume of course) should give you the same or even more AC Voltage at TP107 / 207 which puts the signal to the power amp. If you put signal only to lets say the left channel you should get around 0.0V AC at TP207 whereas at TP107 there should be 0.4V or more and vice versa.
If not check the stereo/mono switch setting and cabling. At TP101 and TP201 you should get the awaited values from TP107/207(in mode stereo).
If you push balance to the right the measured value at TP119 or TP107 should decrease, and pushing balance to the left should increase the measured voltage a bit under the assumption that the tone signal is only .connected to the left channel. To be sure repeat this procedure with the right channel
I went after all connection and cleaned all cables connected to the computer. checked the PCB 4 (was only fitted with 1 screw) put in all screws and tightened all.
P17/20 pin 1, 0.4VAC, TP101, sometimes erratic, but at times stable at 0.38VAC, TP201 stable at 3.8VAC,
TP107/207 Follows volume from 0 to 1.15VAC (full volume), Balance works for right and left.
Linear, filters, loudness and mono, on/off no change
Good work. So now the question is if that is the expected volume range through the pre-amp. From 0.4 to 1.15 is an increase of 2.85 times. If that is typical for the pre-amp section it would appear the problem is in the power amplifier section. If so, what would be suspect that affects both left and right channels to be equally weak?
With FM (Tape1 off) on I measured between TP 109/209 and -35V, 1.6VDC, should be 2VDC
The only thing I can think of having influence on both amp circuits, is the overload circuit, not sure how it works, but if it just turns down and not off, power to the amps that could be it, and maybe the lamp is blown (was new)
sonavor: Good work. So now the question is if that is the expected volume range through the pre-amp. From 0.4 to 1.15 is an increase of 2.85 times. If that is typical for the pre-amp section it would appear the problem is in the power amplifier section.
Good work. So now the question is if that is the expected volume range through the pre-amp. From 0.4 to 1.15 is an increase of 2.85 times. If that is typical for the pre-amp section it would appear the problem is in the power amplifier section.
Normally line level is/used to be (at leat was at the old DIN-norm) 775mV at 0dB. Thats the level you would get out at full power from a normal pre-amplifier.
To me 1,15V seems to be a reasonable level from pre-amp.
//Bo.A long list...
Søren Mexico: I went after all connection and cleaned all cables connected to the computer. checked the PCB 4 (was only fitted with 1 screw) put in all screws and tightened all. P17/20 pin 1, 0.4VAC, TP101, sometimes erratic, but at times stable at 0.38VAC, TP201 stable at 3.8VAC, TP107/207 Follows volume from 0 to 1.15VAC (full volume), Balance works for right and left. Linear, filters, loudness and mono, on/off no change
I don't get it right i think. Have you tried to connect the PC sound out to 1 channel only? Do you then get the AC only at the same channel or is it on both channels at TP107/TP207?
Try the stereo mono switch then if set to mono you should get the same reading at TP107 and TP207 (ok forget about the last digits 1.38V AC is the same as 1.4 V AC at least for the beginning).
If balance works from left to right that's nice, but the balance potis are after the stereo mono switch and do their job well.
What makes me wonder is that both channels are to low with the volume.
The Overload indicator is only a gimmick in my eyes because if the power amp is getting to much input signal it just lights up the overlaod lamp (if not burnt ) but it doesn't have any feedback as far as i can see right now but i might be wrong.
With mono switch ON, no difference, 0.4VAC, and 1.5VAC both channels, Turning of left channel from the signal on the computer left channel shows 0.0, the same goes for right channel.
I will go through the test points for the amp section one by one today, at TP 109 I had 1.6VDC, the manual says 2 VDC, there, with FM on tape off, volume and all controls in "0", maybe I did something wrong in both channels I have been checking all transistors for placement (BCE) and type, I have checked polarity an all caps, I have checked all feeds for correct power, they all shows "0" to 1,5VDC more than required, All the output transistor TIP 142 and 147, With 4 Ohms speakers connected shows the same increase in temp, going from ambient temp. to 25-26°C with volume on "0", with volume on 2/3 (normal listening level) they go to 27-28°C, all of them the same, The Idle current is correctly adjusted and stays stable.
As the PCB5 is attached with the solder side very close to the main switch and some other points, I have made sure that there is NO contact anywhere.
All wires desoldered to get the PCB out was photographed and brought back in the right places, checked against drawing and placement plan. All solder points checked and rechecked several times.
The output TRs are connected, not only with BCE check on PCB, but also checked BCE connection to first component or connection in the drawing.
All TRs mounted to cooling segments, are attached with insulators, micas and heat paste, non of them has ground connection to metal bases.
Søren, have you tried connecting music directly at the amp inputs? Unsolder input caps and solder shielded wires with RCAs at the other side, then use a preamp to feed that. Does it play music well?
Jacques
Music plays well, on FM and CD to Tape input. as for connecting a preamp, I can do that, but I would like to find the failure, and as I have a software oscilloscope, I would also like to learn to use that,
How do I connect the oscilloscope to follow the sound path, ground and then just + on the components??
Søren Mexico: How do I connect the oscilloscope to follow the sound path, ground and then just + on the components??
Søren,
If your oscilloscope is anything like mine you can check to see the quality of the stereo signal produced. A full range will display as wavy lines going in all directions, a monaural signal with display as a pulsating straight line.
In addition weak signal strength with display as a very small cluster, whereas a strong signal will fill the screen.
I am not sure how, in your case to connect the oscilloscope, however I have mine setup going in-between the pre-amp inputs and the preamp outputs, this allows not only the monitoring of the sound spectrum but also FM signal strength and tuning.
Good luck!
Jeff
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Søren Mexico: Music plays well, on FM and CD to Tape input. as for connecting a preamp, I can do that, but I would like to find the failure, and as I have a software oscilloscope, I would also like to learn to use that, How do I connect the oscilloscope to follow the sound path, ground and then just + on the components??
Can you post some pictures Søren? What are you using as your scope probes? On a hardware oscilloscope with the standard probes, I connect the probe to the signal I am measuring and the probe ground to the signal ground. You should now be able to check your 0.4V single frequency, 2K Hz test signal coming in on Tape 1 input and the 1.5V test signal coming out of the pre-amp stage. You can also check the signal at the output of the amplifier at TP117 (L) and TP217 (R). Just be careful and mount the probe with power off so you get it positioned without accidentally shorting something.
When you say music plays well, you mean other than the volume range being too low, right? Did you ever try listening to the 4400 with just headphones?
The test Jacques suggest would verify that the problem is in the output amplifier section. I was hoping we would have been able to find the problem without doing that kind of surgery but it may be the best way to verify there is a power amp problem.
I'm a little drunk now, it was my birthday, so the whole day was open house, and only rock music from 6ties and 7ties, tomorrow work is calling, so until Friday,
Saludos Søren
blah-blah and photographs as needed
Happy Birthday
Sören you have to be careful with software Oscilloscope. It uses the Line-In of your soundcard. The maximum input voltage is limited to 1 - 2 V which give a correct reading with the program. If the AC is higher the signal might 'only' be clipped' (get's distorted) but can make some damage to the line In.
One thing that came into my mind is that you never put a signal at the tape 1 and with disconected loudspeakers switch on the bm4400 and slowly pulled the volume to the max while meauring the output voltage.
With the fact mentioned above there is a way to do this. I don't know what DMM you have but nearly every DMM can measure the effective AC Voltage around 50Hz or 60 Hz quite exact even at higher voltage levels.
So this is what i suggest: set your software tone generator to 50 or 60 Hz (whatever you like) with an output level of 0.7 V AC, connect it to your BM 4400 at tape1. disconnect any loudspeakers and measure the AC output voltage of the BM at every ~10 % of the scale of the volume slider. At the right most position you should get a reading of about 20 V AC (effective). Can you confirm this?
Dom
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RaMaBo:With the fact mentioned above there is a way to do this. I don't know what DMM you have but nearly every DMM can measure the effective AC Voltage around 50Hz or 60 Hz quite exact even at higher voltage levels.
I quite agree with everything you wrote, but there is one caveat when using a DMM like this: many of them will not show the correct AC voltage if the AC you're trying to measure is riding on a DC voltage level. This can easily be the case when trying to measure intermediate signals inside a discrete amplifier circuit.
To avoid this, you need to have a series capacitor on the DMM probe to keep the DC out - but this in itself can be a problem and affect the reading when the frequency is low.
--mika
Hi mika,
that's right, but what i had in mind was to get an idea what the maximum output voltage of the power amp in its current state is. I think there's not a big problem with the unit itself. Just to make it sure (and protect Sören ears from (2x) 75 W 2 KHz (sine, square or whatever waveform he uses from the program ).
Søren Mexico: I'm a little drunk now, it was my birthday, so the whole day was open house, and only rock music from 6ties and 7ties, tomorrow work is calling, so until Friday, Saludos Søren
A Belated Happy Birthday Søren!
One full day without Søren! Come on!
chartz: One full day without Søren! Come on!
I know, it’s terrible, but when the man has to work, the man HAS to work! He’ll be back at it tomorrow.