Another Kenwood CS-4035 question

[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

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

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

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

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

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

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?

[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

1N4007's in series made no difference

[stj]

Re: Another Kenwood CS-4035 question

maybe - if they are fast enough
compare speed

[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?

[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.

[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

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?

[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?

[R_J]

Re: Another Kenwood CS-4035 question

Without the heater working you will not get a display Check R52 (7.5Ω) but it is likely ok, Since the heater is supplied by the same transformer as the high voltage, That is likely missing as well. Check the circuit around Q8.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

Does the heater light up in the crt? it may be hard to see in a bright room. Also check the intensity control, this button should be IN to adjust the crt intensity and pulled OUT to adjust the scale illumination.
On page 30, P12 pin14 is the INT pin, this should vary when the intensity is adjusted.

No, no light at all in the CRT - either end.

And yes, checked the intensity control already.

Off to bed really as it's midnight here but shall check the pin 14 and report back...

EDIT:-

It does vary when the intensity is adjusted

[R_J]

Re: Another Kenwood CS-4035 question

Does the heater light up in the crt? it may be hard to see in a bright room. Also check the intensity control, this button should be IN to adjust the crt intensity and pulled OUT to adjust the scale illumination.
On page 30, P12 pin14 is the INT pin, this should vary when the intensity is adjusted.

[Crystaleyes]

Re: Another Kenwood CS-4035 question

This scope is just down to it's bare skeleton. There is no front panel nor any knobs or buttons connected.

Having a better look, the channel 2 selector (which governs U4) was not where the manual stated for testing. When set properly, the temperature on U4 dropped significantly.

Have you checked the input and output voltages of U4? they should be 0v with no input signal.

Pin 1 is 0.001v whilst pin 8 is 0.102v

Also check the -1.2v (9) and (10)

(9) reads -1.31v and (10) is -1.17v

The sweep circuit may be working but it is sweeping off the crt face due to the vertical deflection not being 37.5v on both plates.

After having a good play around, both plates are now as near as damn it to 37.5v and the DX+ and DX- are also at +68v.

When the DX+ and DX- are each at 68v the beam would be in the center (left to right) this voltage will change as the crt beam is swept across the crt face.

There is still no life on the CRT, so I'm just about to see if there is any HV is present on the TP12.
I don't have a proper HV probe so can't test the -1500v however TP 12 should be between -300 and -650v.

Let's see?


EDIT:

So... no high voltage whatsoever at the TP (R44 - R43). Only 684mV

At least there is some kind of progress now...

Including the schematic below

I'll check the Op-amp and transistors tomorrow

[stj]

Re: Another Kenwood CS-4035 question

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