Another Kenwood CS-4035 question

[Crystaleyes]

Re: Another Kenwood CS-4035 question

freezer spray and hair dryer time.
and consider replacing any zener diodes

Good points, I also hadn't thought to check any zeners. Thanks

I'm probably jinxing myself by saying this, but since pulling the U201 hybrid and reinstalling it, both the 37.5 and 68v points have been present, with the 68v being particularly stable.

As right now I am working back on the area of the PSU board which manages both the HV section and the 80v rail (I seem to remember, which supplies the 37.5v's), hopefully when this is resolved the 37.5's will stop fucking around?

I'm on it now, so let's see?

[Crystaleyes]

Re: Another Kenwood CS-4035 question

So... (I think) this is not working.

It is a Y10GA HV diode (.pdf attached)

It shows nothing on the diode testers I have here, unless reversed in which case it shows as a 13.3v zener, but there is no mention of it being anything zener in the manual nor datasheet

Anyone know anything about these?

[R_J]

Re: Another Kenwood CS-4035 question

Most high voltage diodes are stacked diodes (diodes in series), you can't check them with a meter in diode test, they will check open. Is it D10? it's not likely your problem.
your diode testers don't provide enough forward voltage to check it, looks like it would need at least 22v not the .7v of single junction diodes.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

I saw that. It maybe read as a zener because that component tester tests up to 30v reverse voltage, and yes it is D10

Anyway, after pulling and testing every component in that area, I also put in a socket and a new op-amp, yet still the HV is totally dead.

It had been working before I replaced the missing components on the main board. All of the power rails are present and correct.

This is where a HV probe would come in handy. I can get 1M resistors in town, maybe I'll make something up, voltage-divider style.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

If this is a 6kV diode, then I should be able to string six 1N4007's in series, just to test it out, no?

[stj]

Re: Another Kenwood CS-4035 question

maybe - if they are fast enough
compare speed

[Crystaleyes]

Re: Another Kenwood CS-4035 question

1N4007's in series made no difference

[stj]

Re: Another Kenwood CS-4035 question

disconnect the trippler for now, incase it's drawing too much current

[Crystaleyes]

Re: Another Kenwood CS-4035 question

disconnect the trippler for now, incase it's drawing too much current

If you mean the P9 connector, then that is already disconnected, or do you mean disconnect the actual part in the circuit?

[R_J]

Re: Another Kenwood CS-4035 question

I saw that. It maybe read as a zener because that component tester tests up to 30v reverse voltage, and yes it is D10

Anyway, after pulling and testing every component in that area, I also put in a socket and a new op-amp, yet still the HV is totally dead.

It had been working before I replaced the missing components on the main board. All of the power rails are present and correct.

This is where a HV probe would come in handy. I can get 1M resistors in town, maybe I'll make something up, voltage-divider style.

You had high voltage prior to replacing the parts? If you did, which parts did you replace, maybe there is a clue to what happened.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

I wouldn't have thought so, but they were Q12, Q13 and Q304. (2SC3423, 2SA1369, 2SA1005) All were replaced with the correct components except for a 2SA1015.

Having been working on this PSU again, I am now thinking to resolder all and any joints around this HV section. It really is quite messy in places, as has had various repairs in the past.
When I bought the scope, apart from failed filter caps and a dead hybrid IC, Q8 on this PSU was burnt out and had toasted the board. As the original 2SD1666 wasn't available, a 2SD613 was used instead, yet it still runs way too hot so maybe the issue is on that?

This was one of two identical and dead Kenwood scopes in a job lot.

I know this PSU was working, as I tested it with the functioning main board of the 2nd scope before that one was sold on. Shame it is not still here.

Anyways, I'm about to go and touch up all the connections around the HV area so we'll see what happens?

Thanks everyone for the input

EDIT:-
Retouching the board made no difference, and also retested all the transistors on the PSU board. No failures.
Really need a HV probe, so tomorrow, I'll get some 1M resistors and knock something basic up...

[R_J]

Re: Another Kenwood CS-4035 question

2sd1666 is a totally insulated case. the 2SD613 is not so the collector is shorted to the heatsink, is the heatsink touching anything? Is the collector trace even connected to the transistor?, if not run a jumper wire from the transformer to the collector. I suspect the 2sd613 is meant for audio and not the 50Khz frequency of this circuit.

A high voltage probe likely will not help, If the circuit was working you would have the heater working. It may be that the Q8 transistor needs to be the original as it is a critical circuit, the base is feed by a winding from the high voltage transformer which is how it how it oscillates to drive the primary of the transformer.
I suspect Q12, Q13 & Q304 were on the vert./horz. board not the power supply.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

2sd1666 is a totally insulated case. the 2SD613 is not so the collector is shorted to the heatsink, is the heatsink touching anything? Is the collector trace even connected to the transistor?, if not run a jumper wire from the transformer to the collector. I suspect the 2sd613 is meant for audio and not the 50Khz frequency of this circuit.

A high voltage probe likely will not help, If the circuit was working you would have the heater working. It may be that the Q8 transistor needs to be the original as it is a critical circuit, the base is feed by a winding from the high voltage transformer which is how it how it oscillates to drive the primary of the transformer.
I suspect Q12, Q13 & Q304 were on the vert./horz. board not the power supply.

So, the 2SD613 heatsink is insulated from any circuitry, and the collector is connected with a wire. It was just removed in that photo.

So far I have replaced the op-amp, tested all the transistors and diodes on the whole board, as well as the transformer, HV coil and most resistors and caps, as well as retouching any suspect joints.
Kinda running out of things to test. I don't think U31 has any part to play in this but maybe I'm missing something?

Next step later today, will be to remove and test all the capacitors and remaining resistors. Beyond that, I'll start looking for breaks within the wires.

I wanted the HV probe to see if there was anything coming out of the HV transformer without killing my DMM.

[R_J]

Re: Another Kenwood CS-4035 question

U31? all that does is provide a square calibration waveform for the front test point, it has nothing to do with the operation of the scope.
What was wrong with the original 2sd1666? "burnt out"? what do you mean, was it shorted? if it was NOT shorted, it is likely still good but was running hot

[Crystaleyes]

Re: Another Kenwood CS-4035 question

What was wrong with the original 2sd1666? "burnt out"? what do you mean, was it shorted? if it was NOT shorted, it is likely still good but was running hot

It was shorted.

I have been to all the shops I know but none had it. One shop had the number on the tray, but long since sold out.

2SC3299 2SC3852 2SD1585 are three that come up when looking for an alternative so I'll see if I can find one in the morning?

[R_J]

Re: Another Kenwood CS-4035 question

I checked another kenwood scope (CS-5350) service manual and it uses a 2SD613, so I guess it is acceptable in that circuit.
You do have -10v on the emitter and +10v on the collector? what voltage is on the base?
I take it you have replace both C20 & C21.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

I checked another kenwood scope (CS-5350) service manual and it uses a 2SD613, so I guess it is acceptable in that circuit.
You do have -10v on the emitter and +10v on the collector? what voltage is on the base?
I take it you have replace both C20 & C21.

Emitter is -11.25v, collector is 11.08v and the base is -10.6.

At least that is where the voltages start at, for the transistor heats up too much and the voltages start to drop.

I haven't replaced those two caps, however they were pulled and tested. Both came in at just over 90uF, with negligible Vloss and ESR, so they went back in.


Anyway, looking broader at the schematic I have decided to verify all the test points, which hasn't got off to the best of starts.

TP1 for example should be +193v for example and reads 189.9v. The thing I don't understand is that the corresponding waveform shown has the vert and hoizontal knob settings as 0.5v AC and 2ms per division.
Unless the CRT is 6 feet high, then I am struggling to see how a 193v waveform should be measured using 0.5v a division?

That aside, up to and including TP 6 a clear reproduction of the waveform can be found.

TP 7 is fecked. It should be sinusoidal.

Looks like an LC wave on acid - See attachments

[R_J]

Re: Another Kenwood CS-4035 question

TP1 for example should be +193v for example and reads 189.9v. The thing I don't understand is that the corresponding waveform shown has the vert and hoizontal knob settings as 0.5v AC and 2ms per division.
Unless the CRT is 6 feet high, then I am struggling to see how a 193v waveform should be measured using 0.5v a division?

Look at the schematic. that 193 volts is the DC output of the D1 bridge rectifier, if the voltage is 3 volts low it means nothing! the 160v a/c feeding the bridge could be a couple volts low, C1 could be weak. The line voltage could be a couple volts low. As for the wave form, that is the ripple measured across C1 which according to waveform (1) is 2v p/p. Note the AC after the 0.5v

There is a problem with no high voltage, there are only a few components in that circuit two of which are .50 cent capacitors which check low in capacity, maybe they are ok, but what if they ARE weak causing the circuit not to oscillate

[Crystaleyes]

Re: Another Kenwood CS-4035 question

Look at the schematic. that 193 volts is the DC output of the D1 bridge rectifier, if the voltage is 3 volts low it means nothing! the 160v a/c feeding the bridge could be a couple volts low, C1 could be weak. The line voltage could be a couple volts low. As for the wave form, that is the ripple measured across C1 which according to waveform (1) is 2v p/p. Note the AC after the 0.5v

Thank you for that. Now I understand. (Although I hadn't actually considered the 189v to be a problem)

There is a problem with no high voltage, there are only a few components in that circuit two of which are .50 cent capacitors which check low in capacity, maybe they are ok, but what if they ARE weak causing the circuit not to oscillate

Quite true. Seems to me that the problem must lie somewhere which has already been checked. Perhaps I need to be more diligent?

[R_J]

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?

That aside, up to and including TP 6 a clear reproduction of the waveform can be found.

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.