Iwatsu SS-5711

[Sinewave]

Hi there.

I have an Iwatsu SS-5711 scope, which has just developed a focus issue.

It's not had much use in recent years. Othewise, appears to work just fine apart from keeping a trace in focus.

It'll start sharp, then go out of focus, I can 'chase' it into focus, but it'll wander again. Have tried the astigmatism but it'll go out of focus again.

I think somewhere I may have the manual for it, but I don't think it'll be a service manual.

Thanks.

 

[(*steve*)]

I would be looking very critically at the electrolytic capacitors inside the unit.

 

[Sinewave]

I just found this, couldn't reply to it to ask him how he got on.

https://www.electronicspoint.com/iwatsu-oscilloscope-ss-5121-a-t39427.html

 

[(*steve*)]

That's a newsgroup posting from 2003. Newsgroups are read-only here, and the chances of getting back to him are slim.

Here are a few links that may be useful:

http://www.eevblog.com/forum/reviews/iwatsu-ss-5705-40mhz-oscilloscope-tear-downrepair/30/

http://www.cjs-services.co.uk/?p=101

The second one is especially interesting because:

a) the problem is related to focus (but way more extensive than yours -- unlikely to be the same cause)

b) It mentions extensive issues with electrolytic capacitors (my first guess)

c) describes how he go the technical details needed to repair it.

 

[Sinewave]

Thanks Steve, I'll take a look at those.

 

[Sinewave]

Found one!

The manual has service and maintenance instructions and schematics.

So pretty much now, between myself and any help I can get here, I'll hope to get it sorted.

In the CRT schematic there's the circuits for intensity, focus and astigmatism.

The astigmatism affects focus also, so perhaps it's best for me now to try and trace around the focus and astig circuits and check components.

 

[(*steve*)]

Be careful, the voltages around there can bite.

I'd have a close look at electrolytics in the power supply, and the sections of the circuit you're working on first. As I advised, I'd probably check all of them. Do you have access to an ESR and capacitance meter?

 

[Sinewave]

Hi there.

Well my Fluke 179 measures capacitance but not ESR. I had a glance at the caps, nothing looked odd, but the values may not be as they should.

 

[Sinewave]

So doing a spot of research suggests that with my capacitance meter, it may show a cap to appear to be fine, yet the series resistance may actually show that it isn't.

I may have to invest in an ESR meter.

Thing is at the moment I'm working in cramped areas, moved house a year ago and it still looks as though I moved in last week

I need to invest in a plastic fold away table and antistatic mat to really take this thing apart.

 

[Sinewave]

Another update, which may point me in a certain direction, is that the calibration point which should read 0.6v is reading 0.28v.

 

[Sinewave]

Can I test the caps with an LCR meter in the absence of an ESR?

I've found a poly cap with a crack in it, otherwise, physically things appear ok, but I've no other way of testing the caps apart from my capacitance meter, which shows them as fine, but as we both know they may have developed a resistance.

I'll pop some photos up in a bit, I'll see if I can get a good photo of the cracked cap.

 

[Sinewave]

Here we are on the bench

Power supply board out

Cracked cap

 

[(*steve*)]

Well, replace it. Where was it? Anywhere that might be connected with the problem?

No, ESR can't be checked with an LCR meter.

Have you had a look at all the electrolytic capacitors for signs of problems (leaking electrolyte, bulging tops/ends, etc)? If you find *any* then there may well be more you can't see.

Are there electrolytic capacitors that are near heatsinks or other hot parts?

I'm concentrating on this because it has been reported as a known issue, and is a simple one that you should try to eliminate first.

If you were around the corner I'd come over with my ESR meter.

 

[Sinewave]

Well, replace it. Where was it? Anywhere that might be connected with the problem?

No, ESR can't be checked with an LCR meter.

Have you had a look at all the electrolytic capacitors for signs of problems (leaking electrolyte, bulging tops/ends, etc)? If you find *any* then there may well be more you can't see.

Are there electrolytic capacitors that are near heatsinks or other hot parts?

I'm concentrating on this because it has been reported as a known issue, and is a simple one that you should try to eliminate first.

If you were around the corner I'd come over with my ESR meter.

Indeed, yes it'll be replaced, this one is in the power supply circuit. Yes I've been looking and physically things appear ok, checked the electrolytic caps for any signs but couldn't see anything.

I'm following your advice to eliminate them first, but as I don't have an ESR meter all I can do at the moment is look at them. I could either just replace all the caps or get a meter and test them first.

If you were around the corner I'd put the coffee on and wait for you to come over with your meter

 

[Sinewave]

Ok, well have been doing what other tests I can to the caps until I get my hands on an ESR meter.

With my multimeter set to read capacitance, I'm getting between 4550 and 4800 mic farads for a 4700 mic farad electrolytic cap - so reads ok.

But on an LCR meter, at 120Hz, it's reading 03.61 milli farads - so maybe a bad cap found so far but without an ESR reading, until I can get an ESR meter?

 

[(*steve*)]

At the very least, I'd compare the readings of your LCR meter with your capacitance function using a known good capacitor.

I presume both of these measurements have been taken out of circuit?

Do you have another scope? Here is a method of testing ESR. It's essentially what the ESR meters automate.

 

[Sinewave]

Hi yes I took some readings in the same manner from a known good cap.

Readings were done with one end desoldered out of circuit.

I can get access to another scope, but if I feel it's worth me having my own LCR meter, I've got my eyes on one which also has an ESR function.

http://www.agilent.aspen-electronics.com/media/pdfs/5990-7778EN.pdf

 

[Sinewave]

I've got a diode measuring (Fluke 179 on diode range) 2.4v one way and 0.26v the other way, so I assume that's shorted. I think it's a Schottky diode, manual says 1SS16, but I can't find one or cross reference one. There's no other specs in order for me to find one myself.

Any idea? Thanks.

 

[Sinewave]

That's the one, sticking up. Service manual only says its a 1SS16.

 

[(*steve*)]

Do you have the schematic? What symbol does it show for this device? (normal diode, schottky diode, zener diode, etc...)

That meter looks like a good tool. Probably out of my price range though