Amplifier Repair - electrolytic capacitors expose metal top?

[elebish]

Hi I am new to electronics fault finding, why when i touch dvm probs to ground and the top exposed metal part of an electrolytic can i see a voltage please?

Typically, radial lead caps have leads that are isolated from the can which is probably aluminum. In that case, a dc voltmeter with 10 meg ohm input could read some voltage from can to chassis or PS gound since 10 meg ohms offers no real load to the voltage. Axial lead caps usually have one lead connected to the can and must be negative. Another thing to consider is that chassis ground is not always PS ground. Chassis ground could also be above PS ground and in some cases, be below PS ground. Then there is AC input ground to consider. (That's another story!) Always use an isolation transformer to supply ac to the item you are working on.
Back to your question: The exposed can of a radial lead cap could read a voltage if the cap is leaking or shorted. That is not likely. Most caps are faulty because the dielectrics are leaking, shorted or open. Electrolytic caps are designed to pass a small amount of ac or fluctuating dc but will block steady dc. There are also ac caps used for motors etc, that are designed to operate by passing a large ac current at the rated voltage.

 

[looxuser]

Thanks for the info on the Caps elebish

 

[73's de Edd]

looxuser . . . . . . . . .


Finally . . . .able to get back to your problem.

AMAZING . . . . to have a few bits of ancillary instrumentation . . . .I usually have to instruct in "Mac Guyver" types of workarounds, much in the order of very sneaky utilizations of Scotch tape, toothpicks and clarinet reeds.

Considering your being able to hook up the main unit and the tuner, and getting a feeble semblance of audio "bleed thru" info.

Lets use that observed, given effect to start our troubleshooting.

It so happens that the audio output level from your tuner audio connector is being right at the expected drive level of the input of the STK Power output module.

Look to see if I did put the correct one ( STK ), of a possible two, as being the inset to the right of the block diagram of signal flow thru of the set . . . . . . is it right ?

The very first test would involve the coupling some of that tuner output audio across to the STK input.

Soooooooo just in case you have palsy and can't do "touchy" readings with slippery meter probes, lets get a piece of insulated, yet tinned, hook up wire that can reach from Pin 14 of IC601 / or / 602 . . . .across . . . ..to pin 18 / or / 1 of the STK modules pins.

Initially do a solder tack on of one end of the wire to anywhere along the common connective buss being between #2 of your tuners audio output to Pin 14 of IC601 / or / 602.

Wherever its the easiest for you find and make connection.

The other end of the hookup wire has my earlier posts mentioned AC couping / DC isolation capacitor being solder tacked to it.
You now power up with connected speakers or headphones and temporarily touch the free lead of the capacitor to the pin (s) 18 or 1 of the STK module.

If the planets are now precisely aligned at this instant in time , you shold now hear the highest sound level you have heard since . . . . you don't know when ? . . .coming out from that units speakers or headphones.

Move the cap to verify output from both pin (s) 18 or 1 . . . .confirming both channels are working . . . but with no volume control capability, since they are being earlier in the audio flow path.

If this passes, then we move on to the next logical test sequence, it being at the at the function selector I.C..

BTW . . .is the sig generator is being an AF spectrum one, and NOT a higher frequency RF generator . . . . if its being needed later on.


73's de Edd

 

[looxuser]

Hi 73's de Edd, and thanks for getting back to me, now you've said do this initial test, seems obvious to me yet I didn't think of that. so here is a diagram representing what you are saying.
Clearly i would touch to ic851 inputs on pins 1 and 18 in turn. Is this what you mean please? Just interested but what function does the Cap 0.1 - 1uF perform in this test?

Yes its IC 4182II that is fitted, the 18 pin version (you were right the diagram should pin 8 as input when it is rightly 18)

Re the function generator its something my father made back in the 80's when electronics were a hobby for many. It can generate sine, saw tooth and square waveforms from x0.1 to x1000 Mv at frequencies x1 to x10Khz. Ive checked it and can see some of these waverforms on the oscilloscope if we need them. Regards of this repair, my learning will be enhanced ten fold if I learn to test using generator and osc. Let me know if I've got your instructions right in my diagram and i'll crack on with that. Kind Regards.

 

[73's de Edd]

looxuser . . . . . . . . .

You are exactly right on your drawing and technical supposition.

The reason I gave such a variance of the coupling capacitor value was your possibility of having to look hard
just to find ONE of those capacitor values.

Sounds like your dad might be looking up at forty plastic storage drawers, and having choice of any of those values that I had given.

End result is that a .1 ufd cap would make audio sound a bit tinny, while the highest capacitance would additionally be passing more
of the audios bass spectrum .

The purpose of the cap is to pass AC signal thru, but to not pass any DC.

If not being utilized, one circuit could be having a completely different DC level on it, from the other circuit and
the produced DC voltage /shift /balancing could cause a transition in the designs operational parameters of one stage, or both.

73's de Edd

 

[looxuser]

Haha, yes you read that right he has a large garage filled with stuff including electronic components. I'll give this a shot tonight and let you know how i get on cheers

 

[looxuser]

HI 73's de Edd, well I tried as you suggested and some result. The sound was not deafening but much louder than previously so i suppose that proves IC851 working, i went ahead and tested same method either side of resistors R851 & R852 with sound once again being played through speakers. Ready for the next step as you see it please?

 

[73's de Edd]

looxuser . . . .


The next move is proceeding to confirm operation of yet one more gain stage that is being just before the STK power module that you just tested successfully.

You will be using the same tuner derived test audio coming in thru that isolation cap.
It can be connected to at either IC681 pin 5 or at the labeled [E BOARD VOL C.B.] and its connection 4 is being the same one of interest.

That circuit schematic is on AIWA manual page 10 or Adobe's page 9

If you get equal volume as before, or hopefully, even more, you then move even earlier in the input circuitry to connection 4 of the [E BOARD VOL C.B.]

With the test audio at this stage, you will need to check your volume control to see if it is functioning, as it is now being in circuit, leave at max . . .if tolerable .

That's it, until I see if you have any techno or test point "locating" snags. GPS can't help us here.


73's de Edd

 

[looxuser]

HI 73's de Edd thanks for getting back so swiftly, can I just check something with you though please. tracing back on the schematic (chuckle without a GPS), I cannot see IC681 to which you refer and the label E BOARD VOL C.B. I can see the Buffer Amp IC803 & 804 and ahead of that IC801 the electronic vol. Also for me page 10 of aiwa diagram shows BBe adjustments.

Can I assume that its safe to inject that isolation cap signal we are using to any IC's that indicate an audio input / path please? You mentioned need for another cap.

Just as an aside and my learning, am I right in saying the the input attenuator with the ops amps and arrangement of transistors to ground is the way the unit deals with differing inputs, ie depending on the function selected determines which array or combination of resistors affects inverting / non inverting feed to the Op AMps. effectively "attenuating" all sources to similar levels?

 

[73's de Edd]

looxuser . . .


Can I assume that its safe to inject that isolation cap signal we are using to any IC's that indicate an audio input / path please? . . . . .YEP.
You mentioned need for another cap. . . . .That's for when we get to the testing of the electronic function switch

I now see that there is no IC680 just an IC681, as it is having TWO sections , one for right and one for left channels.

Helping you thru the forest now . . . .
On the board that your STK power amp is being mounted, along that one edge of the board.
Estimate the board dimension to the very bottom of that board from your STK , and stop about 1/3 of the way down fron the STK.
Then estimate the left to right dimension of the board and move your referencing from the prior position until you are about 60% to the right from the boards extreme left side referencing..
There should be a single inline package IC, marked as IC681 and is being a NJM4558 dual op amp.
Inject the same tuner audio into its pin 7 and it should produce about the same increased audio level as was produced back at the pin 1 of the STK module on out initial test .
And then . . .AND THEN . . . . we should expect a greater volume if we inject the audio into pin 5 of the IC681 op amp.

Waiting for test results . . . .

73's de Edd

 

[looxuser]

Hi 73's de Edd, I still cant locate the Op Amps you are referencing and begin to wonder if i posted the correct service manual, regardless i have located op amps IC603 1 & 2 and can see these sit after the IC601 function switches we took the audio feed from so i'll test those IC 603 at both the incoming side of the LCH op amp pin 5 and the outgoing pin 7 and then move to RCH of the other OP Amp and do pin 3 and 1 respectively and let you know. Many thanks

 

[looxuser]

Hi there , so here is the latest, I tested the dual Op Amp named "input attenuator" IC603 as suggested. Yippee, when I injected that audio signal at pins 3 or 5 I got audio right through to the speakers and at some considerable volume, controllable by the front panel volume control and with bars reacting in the Graphic equaliser. Groan, I got nothing however when injecting at the output of the Op Amps pins 1 & 7.

So we know we have an audio signal into IC601 & IC602 because thats what we've lifted for testing purposes from track that feeds pin 14. So is it a reasonable assumption that these IC's are not switching that signal to feed the input attenuator and that they are not likely both defective. I checked the power supplies once more then to IC 601 & 602. Circuit diagram gives +9v at pin 16 and -8.5v at pin 7. I'm reading 8.9 & -8.4 with my DVM so seems good. Measured resistance to ground pins 4, 6 & 8 and at 10ohms for each seemed ok.

Turned my attention the to what controls these two switching IC's and thats IC604 and I checked voltages again to that, expecting to see 8.5v at pin 16, get 8.2v. So R635 is in series to pin 16 and I get 8.9v one side and 8.2v the other. 8.2v seems low but maybe ok. So, then looking at links IC 604 F-A, F-B, F-C and these each have a 1k resistor in series, these resistors are fine. So now looking at the truth table to see whether I have 8.5 volts Hi or zero volts LO in any combinations coming from IC604.

Notice there are afew components that link off the F-A, F-B & F-C interconnects between ic604 to ic 601 & 602. I wonder if some fault with these could prevent the HI LO signals on the control inputs of IC HD14051BP? Thoughts?

 

[looxuser]

Hi 73's de Edd, so I took a look at the truth table and realised the IC is stuck in configuration for Video 1-DAT input so I connected my iphone to this input and guess what it plays music fine and at loud volume if wanted. You can press other source buttons and hear the same music at lower volume. So it seems there is an issue with crossover of sources and actual clean selection of music source which is good news as it narrows the search field. The big question is why? please help.

 

[73's de Edd]

Sir looxuser . . . . . .


I was starting at the rear of the audio chain and working forward, but where you are now is way up at the front of the chain and is where we would have ended up.
Thereby, you have bypassed all of the complexity of the switching involvement of the Surround Sound, BB and Dolby circuitry.
So . . . . YEAAA . . . lets just continue from where you are now.
First lets see if page one of your service manual is marked at the very bottom with SM as in Service manual Code 09-954-101-501.
Then our contained info and referenced pages will coincide.
Digital page 12 . . . .far right top corner of the page IC 141 and 142
Lets check out that input selector now, which utilizes a pair of BU4051B digitally addressable CMOS switches inside of it.
It has capability of 8 inputs , but only 7 are needed to be used on your unit.
First confirm that when switching between Tuner-Deck-CD-Phono-Vid1-Vid 2 that those words are being properly displayed on the frontal display of the unit.

Move to one of the 4051's and confirm a power supply voltage of about 5.6 VDC on pins 16 of both IC's, while using pin 8 for negative probe . . .ground . . .position .
Any loss of that voltage presence, would account for no switching action in this selector function IC.
We have one chip for the right channel and another for the left channel, so I would NOT expect a failure of BOTH chips as a random coincidence.
Another condition affecting BOTH chips would be their common digital address line .

The same digital address lines that perform that display function also are fed to the 4051 on its pins 9-10-11.
Sequentially flip thru the input selector switch positions, in order to get a reading of the address lines for each input position.
Draw out a truth table for the voltages present at those pins for each of the input switch positions . . . . basically a high voltage for a logic high and a low voltage for a logic low.

I'll start you out: (Hypothetical readings )

Tuner Pin 9 ( 5V ) Pin 10 (0) Pin 11 ( 0V)

Deck Pin 9 (0) Pin 10 (0) Pin 11 ( 5V)

Ya da ya da yah . . . .

That way we can confirm that no erroneous address data is getting to the IC's 9-10-11 address lines.

Catch up time . . . .

73's de Edd

 

[looxuser]

HI 73's de Edd, been away afew days hence no reply sooner. Thanks again for your ongoing support.

Responses thus:-

First lets see if page one of your service manual is marked at the very bottom with SM as in Service manual Code 09-954-101-501.
No don't think that the right manual god knows how that happened. I'll try to mail it you or something
Digital page 12 . . . .far right top corner of the page IC 141 and 142
Infact these are IC's 601 & 602 HB4051BP
It has capability of 8 inputs , but only 7 are needed to be used on your unit.
Each has 16 pins
First confirm that when switching between Tuner-Deck-CD-Phono-Vid1-Vid 2 that those words are being properly displayed on the frontal display of the unit.
Yes they do indicate the source selected on the frontal display correctly.
Move to one of the 4051's and confirm a power supply voltage of about 5.6 VDC on pins 16 of both IC's, while using pin 8 for negative probe . . .ground . . .position .
Any loss of that voltage presence, would account for no switching action in this selector function IC.
I will check this again at pin 16
We have one chip for the right channel and another for the left channel, so I would NOT expect a failure of BOTH chips as a random coincidence.
Agreed, neither would I
Another condition affecting BOTH chips would be their common digital address line .
Have traced those lines and resoldered connections to cover any dry joints etc. Will examine again though
Sequentially flip thru the input selector switch positions, in order to get a reading of the address lines for each input position.
Draw out a truth table for the voltages present at those pins for each of the input switch positions . . . . basically a high voltage for a logic high and a low voltage for a logic low.

I'll start you out: (Hypothetical readings )

Tuner Pin 9 ( 5V ) Pin 10 (0) Pin 11 ( 0V)

Deck Pin 9 (0) Pin 10 (0) Pin 11 ( 5V)
Thanks will do that and get back, did try that briefly and the voltages didn't seem to change regardless of source selected and truth tabled out to Video DAT which is when i tried an input through that external connection and it worked perfectly.Like i say will try again for a more definitive answer

Best Regards, Andy

 

[looxuser]

HI 73's de Edd, I'm getting 8.91v at pins 16 of those 4051's so not as low as you suggested but that is in line with what is shown on the circuit diagram. Also -8.41V at pins 7.

So moving on and checking that truth table you suggested on both 4051's I am getting (6.4v) at pin 9, (0.08v) at 10 and (0.01v) at 11, regardless of the input selector switch position. Its as if its locked to binary C Hi B lo A lo which corresponds to source video dat 1 IN. when that input source is selected the sound from an ipod connected to that is loud and clear but the same sound can be heard on any of the other sources but at a much lower volume as if there's some crossover.

I did some further tests on outputs from IC604 A,B,C which feed the two 4051's and got 8v at the F-C pin so therefore Hi and Lo at B & C tallies which what being seen at 4051's albeit at lower voltages but that signal does go through some 1K resistors on the way (all three test ok btw). I get 8.3v at pin 16 of IC604 which is lower than the 8.5 shown on diagram but not by much.

Could I just ask you some related questions for yes no answers thus please:-
a. The master switching ic 604 gets its signals digitally via the INPUT, CLK and DATA lines from the front panel?
b. That same IC not only instructs the LCH & RCH 4051's to switch but also switches banks of resistors and transistors to attenuate the differing sound inputs associated with the attenuator amp IC 603 1/2 (Where we have been injected our sound source)?

Could you share with me your thoughts on how IC604 gets its signal to switch the input source and what could interfere with that (i.e I see some iss133 zeners in there at D605 & D606 and what looks to be a 47μF 10v electrolytic at C607 also a small 330pF poly cap at C647 to GND) and at the other end the three signals to those 4051's also parallel off to what is labelled as the "function video 1:6.6" which includes again an iss133 zener, to base of Q952 PNP resistor transistor DTA144ES.
Would appreciate any further suggestions you may have as feel we are really close to the fault here. I suspect it gets more complicated at this point to prove the functionality of IC's but i'm happy to try.
Kind Regards, Andy

 

[73's de Edd]

.



Sir looxuser . . . . . . . . . .

Since you initially used a "high density" temporary storage site for your initial posting of this units schematic, can you do it again, as apparently we are using schematics with a bit of discrepancy of assigned component identifier numbers .
Naturally the old schematic referencing, has now transpired on its time limit .



73's de Edd

 

[looxuser]

ok hopefully you now have the required schematic, here is an images of relative resistor sizes. Ive assumed smallest ones to be lowest wattage?

 

[looxuser]

Thought to share an annotated image of the board itself topside for interest.

 

[73's de Edd]

.



Sir looxuser. . . . .

Of the resistors shown, we would be wanting to use the smallest ones with long leads.
With a value of approx 1K to manually address in a logic HI signal and the lower 100 ohm or so resistors to manually address in a logic LO signal

We are involved with 3 CMOS logic IC's the IC601-602 pair of CD4051's which switch between the audio inputs and the
IC 604 which takes a serial signal from the u/p's buss and converts it to the 3 address lines going to the CD4051's pins 11-10 and 9.

I believe that you said that is currently "stuck" on a LO-LO-HI into the 4051's and giving a fixed Vid 1 switching position.

What needs to be done first is to either solder suck or solder wick or use a combinational procedure to have pins 3-4 and 5 of the CD4015 / IC604 totally floating.
Confirm by placing metering in ohms mode or diode test and stab a pointed probe into the copper foil right beside a floating pin 3 and then stab the other probe in just beside it and confirm a short.
Then lift the second probe and ever so gently touch the floating pin to confirm that it ACTUALLY is now floating.
Use the identical procedure on the copper foils surrounding pins 4 and 5.
We now just have to see if the 4051's will respond and do their switching changes when being manually addressed.
Work with one channels 4051 at a time and its connections .

Power down condition:

TAPE POSITION TEST:

Switch the display to TAPE position.

Initially take the low value resistor and flux and tin the ends of its long leads for solder tacking to IC pins.
Solder tacking a 100 ohm resistor between pin 8 on one end and 11 on the other end.
Solder tacking a 100 ohm resistor between pin 8 on one end and 10 on the other end.
Solder tacking a 100 ohm resistor between pin 8 on one end and 9 on the other end.

That should establish a LO-LO-LO address code and when the set is powered up. If you inject that audio sample from the tuner
via its isolation capacitor to pin 13 [ TAPE ] input we can hope that a strong audio signal will be coming from the speakers.


I think that you are now fully seeing the use of the different resistors for getting a LOW from off pin 8 and getting a HI from off pin 16.


TUNER POSITION TEST:

Switch the display to TUNER position.

Solder tack a LOW value resistor with pin 8 on one end and 9 on the other end of the resistor.
Solder tack another LOW value of resistor with pin 8 and on one end and 10 on the other end of the resistor.
Solder tack a HIGH value of 1K resistor with pin 16 and on one end and 11 on the other end of the resistor.
If you inject that audio sample from the tuner via its isolation capacitor to pin 14 [ TUNER ] input we can hope that a strong audio signal will be coming from the speakers.


PHONO POSITION TEST:

Switch the display to PHONO position.

Leave the pins 9 and 11 at their previous LOW addresses
Solder tack a HIGH value of 1K resistor with pin 16 and on one end and 10 on the other end of the resistor.
If you inject that audio sample from the tuner via its isolation capacitor to pin 15 [ PHONO ] input we can hope that a strong audio signal will be coming from the speakers.


CD POSITION TEST:

Switch the display to CD position.

Leave the pin 9 connection at its previous LOW address.
Leave the pin 10 connection at its previous HIGH address.
Solder tack a HIGH value of 1K resistor with pin 16 and on one end and 11 on the other end of the resistor.

If you inject that audio sample from the tuner via its isolation capacitor to pin 12 [CD ] input we can hope that a strong audio signal will be coming from the speakers.

If all of these tests pass, we need not concern ourselves of an internal malfunction in the pins 9-10-11 of the 4051's..
This CMOS family usually fails in the manner of having a constant , unalterable LO on one of its inputs.
When you manually addressed those lines you simultaneously were doing both 4051's, so if you were WALKING the test Audio input between the R and L audio inputs of both 4051's you were doing a complete test of BOTH channels .

Stopping to see if you encounter any snags or require a more exacting procedural info.

Pending prior success . . . . .next willl be the IC 604 evaluation to see if it is the fault of the adddress corruption, the serial digital stream that it receives is being the same signal that addresses your display which responds and it changes display input I.D.s properly, so maximum suspicion is to that 2 Amellican dollar /Euro CMOS IC604 chip, as of now.

(I would have placed on a relevant schematic clip, but that schema page is quite whitened out / low contrast and has some line breaks.)


73's de Edd



..