Another Kenwood CS-4035 question

[Crystaleyes]

Re: Another Kenwood CS-4035 question

Where did the scope image come from in post 37? Did you scope that point and get that waveform?

It came from TP7 - The transformer side of R24

[R_J]

Re: Another Kenwood CS-4035 question

It came from TP7 - The transformer side of R24

So test point 6 is ok??? approx. 35v p/p ? Since you have another scope... check what is on C21+ and C20- if the caps are good the ac ripple should be next to zero. That waveform looks like something is killing the oscillation, check the waveform on the heater winding

[Crystaleyes]

Re: Another Kenwood CS-4035 question

So test point 6 is ok??? approx. 35v p/p ? Since you have another scope... check what is on C21+ and C20- if the caps are good the ac ripple should be next to zero. That waveform looks like something is killing the oscillation, check the waveform on the heater winding

Shall do, but need to hit the sack now as it is past midnight and I don't wanna turn into a pumpkin (again)... But I'll check those in the morning and get back.

If you think of anything else to test, I'm all ears...


Thanks again.

[R_J]

Re: Another Kenwood CS-4035 question

I did not know you had another scope, I thought you sold the other one. That waveform looks like the primary winding is just being pulsed and shutting down. One pulse on the primary, leads to the large pulse on the secondary, which then just fades away until another pulse on the primary.
So also check the waveform on pin 4 of the transformer (Q9 collector) It should be a nice sine wave like wf6 but smaller.
Something else to try would be to disconnect the high voltage block (W1) disconnect the jumper E, then see what the waveform 7 looks like.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

I did not know you had another scope, I thought you sold the other one. That waveform looks like the primary winding is just being pulsed and shutting down. One pulse on the primary, leads to the large pulse on the secondary, which then just fades away until another pulse on the primary.
So also check the waveform on pin 4 of the transformer (Q9 collector) It should be a nice sine wave like wf6 but smaller.
Something else to try would be to disconnect the high voltage block (W1) disconnect the jumper E, then see what the waveform 7 looks like.

I've picked up a few broken scopes over the last few months for silly money, and the one in the pictures I only got working last week, but I haven't checked any cailibration other than the LV rails yet.
Actually just bought another Tektronix scope this week too.
That is one good thing about being in a third world country is that hardly anyone actually does component level repair, so some real bargains can be found for non, or partly-working stuff.


As for the readings, I have just started over again and 1 to 4 are as pictured in the manual, although they are not solid, they are pulsing.
TP 6 is actually not 'clearly' a sine wave, and it sometimes appears to have a ghost image on top. (see photo #1) and sometimes not (photo #2)

TP 7 shows no signal with jumper E disconnected

Q9 Collector gives the wave in photo #3

C20 and C21 both show AC ripple of about 500mV

Reading into the manual it says that Q8 should oscillate around 50kHz yet the DMM senses no frequency other the mains

[Crystaleyes]

Re: Another Kenwood CS-4035 question

More info...

The HV transformer coils all have continuity.

Pins 1+2, have around +11.06v and between 32 to 35kHz (depending on which measurement).

Pins 3+4, have around -10.55 volts across them, and the same frequency

Pins 6+7 fluctuate anywhere between -1v to over -130v DC with no frequency

Pins 11+12 appear to have absolutely nothing on them, although the coil measures 6.8Ω with the power off.


Apart from wondering if perhaps the transformer is fecked, the fluctuating output of pins 6+7 needs to be resolved?

[stj]

Re: Another Kenwood CS-4035 question

resistance between 5 and 7???

lift one end of R52 and recheck the voltage at 11,12

btw, did you replace the caps at c17,20 and 21?

[Crystaleyes]

Re: Another Kenwood CS-4035 question

resistance between 5 and 7???

lift one end of R52 and recheck the voltage at 11,12

btw, did you replace the caps at c17,20 and 21?

Yes, C17, C20 and C21 were all replaced

Actually I made a mistake. Had confused the secondary coils pinout.

Pins 1+2, have around +11.06v and between 32 to 35kHz (depending on which measurement).

Pins 3+4, have around -10.55 volts across them, and the same frequency

Pins 5 to 6 is ~6.8Ω with ~17kHz - Negligible voltage
Pins 5 to 7 is ~1.600kΩ and has ~33kHz - Negligible voltage
Pins 6 to 7 is ~1.590kΩ - ~18kHz - Negligible voltage

Pins 11 + 12 are the ones fluctuating wildly, but do have up to 35kHz too

Lifting R52 makes no difference to the secondary outputs

As for pins 5, 6 and 7... A short circuit after a semi-conductor gets switched on?

Maybe I'm being a bit thick, but for example, with R52 lifted, the 11 + 12 coil should be open-circuit. Surely it should behave as a normal secondary with no load connected? It should give a voltage reading across it. Unless the voltage is above 1000vdc and my meter has some serious over-voltage protection which I'm unaware of?

Gonna lift R55 to make sure..

[stj]

Re: Another Kenwood CS-4035 question

pins 1 and 2 are the primary,
pins 3 and 4 are the feedback that creates self-oscillation.
when 3 and 4 have voltage the transistor Q8 turns off killing the primary,
that causes the voltage to drop on 3 and 4 allowing the transistor to turn on again.

11 and 12 are the heater drive, usually between 6 and 10v

5 is output common
6 is the 140v output - but at AC it wont look like that - check the cathode of D11
7 is the HV and the schem says -1500v but again you need to meter it after the diode/cap at R56 or p9

obviously all the windings will be oscillating at the same frequency.

[stj]

Re: Another Kenwood CS-4035 question

if you still have a second matching scope, i'd swap the transformer.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

if you still have a second matching scope, i'd swap the transformer.

Unfortunately not...

Trying to think how I can confirm the transformer is at fault?

[Crystaleyes]

Re: Another Kenwood CS-4035 question

Well, I've the pulled the transformer to see if anything is obviously wrong, and I can see that there might be a problem.

There are no shorts between the coils and measuring off board and with a component tester gives the following readings;

Pins 1 + 2 = 0.19Ω

Pins 3 + 4 = 0.11Ω

Pins 5 + 6 = 953.6Ω / 318.3mH (36pF)

Pins 5 + 7 = 803.5Ω / 261.9mH (43pF)

Pins 6 + 7 = 6.65Ω / 3.06mH

Pins 11 + 12 = 0.14Ω


The problem is that any reading which includes pin 5, occasionally comes up as a 'capacitor' measuring 10's of picofarads, not always, but only with pin 5 (Gnd), so I'll have a good look in the daylight and see if the solder has come loose or dry? Still unsure about the HV diode D10 too.



...I told you I should have set fire to this scope the other day...

[Crystaleyes]

Re: Another Kenwood CS-4035 question

pins 1 and 2 are the primary,
pins 3 and 4 are the feedback that creates self-oscillation.
when 3 and 4 have voltage the transistor Q8 turns off killing the primary,
that causes the voltage to drop on 3 and 4 allowing the transistor to turn on again.

11 and 12 are the heater drive, usually between 6 and 10v

5 is output common
6 is the 140v output - but at AC it wont look like that - check the cathode of D11
7 is the HV and the schem says -1500v but again you need to meter it after the diode/cap at R56 or p9

obviously all the windings will be oscillating at the same frequency.

Thank you. Very interesting.

Are you saying that the primary 'induces' a voltage into the feedback coil? And the primary is fed by the same AC signal which is seen in TP 6, or is it by the oscillating DC?

The op-amp is to regulate the voltage?

[stj]

Re: Another Kenwood CS-4035 question

the primary side is fed by the +-10v wherever that comes from.
and yes, the op-amp tweeks the feedback to regulate the output

[Crystaleyes]

Re: Another Kenwood CS-4035 question

Must say, considering that the HV transformer is not realistically possible to find a replacement, I'm getting very close to moving on from this. Either selling on for parts, or stripping it down and selling the super-rare hybrids, CRT, mains transformer, buttons etc.

After reinstalling the HV trafo, not a lot, if anything, has changed.

The only thing I can still think of is that the 2SD613 really NEEDS to be the correct 2SD1666 in order to work? (although I am sure it was working before)
So unless there are any more ideas, then it is probably time to take it on the chin and do something else.

Picked up a Tek 2215 this week for example, which needs the sweep cleaning up...