Tektronix 475 repair assistance

[Specmaster]

Thats really cool, so a digital scope can be a really useful diagnostic tool on the bench then as well making easier to measure periods, voltages and frequencies then. Hmm I wonder though if any of them will still be around and fully functional in 30 years time?? 

[bd139]

Yes it measures just about everything automatically for you. It even does protocol decoding of SPI/serial etc. The analogue scopes are just interesting toys that I couldn't have afforded until they got to 30 years old. They're engineering marvels

Will it be around in 30 years? Hell no it'll be in the WEEE skip in 5-8 years.

Then again if we look at the "2017" price of a Tektronix 475 (with DM44) - US inflation, currency exchange, add VAT:

Tektronix 475: £15,599
Rigol DS1054Z: £349

I could buy a new Rigol every year and still be up on cash over a 475 made in 2017!

TBH I am supposed to be getting rid of the Rigol but the person who was going to buy it did a runner. I thought for a bit that I couldn't justify the expense but I'm less bothered now I've used it to debug some complicated things.

[Specmaster]

Maybe I'll put it on my Christmas list and see if one turns up, I think hell would freeze first though 

[bd139]

I only got mine because someone died!

[bd139]

Well replacing a few more tants has definitely fixed the HV issue. There was one periodically pulling the 15v line down. Bonus. At least the debugging methodology worked!

However time's up on this one. I have decided that I can't be bothered to fix the z-axis at high sweep speed issue on it now as I'm getting behind on a few projects so I've chucked it on ebay for the next person to deal with. I may have sinned against TEA there!   

[Specmaster]

What, you mean that there's a 475 out there on Ebay after all the work and money you spend on it, WOW I'm flabbergasted  Expect you're thinking now that you should have kept your 1740A 

[bd139]

For me, it's the journey that and the acquired skills and knowledge that counts.

I give it a week before I have another scope!

[Specmaster]

Just had a look at it, she looks great, hope you get your money back on it at least after the effort you have put into her. I doubt it will long before someone snaps her up 

[bd139]

Time will tell.

I spent total £68 so some beer money on top of that would be good

[bd139]

You know what. I can't actually point the gun at this one. I've taken it down again

[Specmaster]

Haha, I wondered if such an event might happen, you was taking it to the grave with you. 

Seemed a shame doing all that work and then letting someone else have the benefit of it. 

[bd139]

Yeah. Mental battle ensued. Plus I’m a member of the church of TEA and that would be going against the good teachings.

[tautech]

Well replacing a few more tants has definitely fixed the HV issue. There was one periodically pulling the 15v line down. Bonus. At least the debugging methodology worked!

This ^ !
Did you grab a screenshot ?

Correct me if I'm wrong but isn't this the rarely observed tantalum repetitive breakdown ?
I've heard it referred to as sputtering but according to Wikipedia that's not the right term. 

[bd139]

I think it is indeed that. And no I didn’t get a screenshot. It was a relatively uneventful affair. There was a 5ms fall from 15v to 3v and then it cleared itself.

Finding the f*cking thing was a problem. I went round all of them on that rail with the bench meter on relative ohms mode and replaced the 5 with the lowest resistance. Then goto 0 until fault cleared. There was one suspiciously low at 39 ohms, which is enough to draw some current at 15v. Whatever it was it was in that batch!

[tautech]

I think it is indeed that. And no I didn’t get a screenshot. It was a relatively uneventful affair. There was a 5ms fall from 15v to 3v and then it cleared itself.

Finding the f*cking thing was a problem. I went round all of them on that rail with the bench meter on relative ohms mode and replaced the 5 with the lowest resistance. Then goto 0 until fault cleared. There was one suspiciously low at 39 ohms, which is enough to draw some current at 15v. Whatever it was it was in that batch!

For those that have not experienced it ( I haven't) could you rig up the faulty one across a bench PSU, maybe with a series resistor so it won't fry immediately, or current limit it and take some scope screenshots ....fast timebase, slow timebase.
It's so uncommon it's worthy of a separate thread............

[bd139]

I would but it’s in the bin already. Plus when I pulled it I snipped the leads off at the body.

[tautech]

I would but it’s in the bin already. Plus when I pulled it I snipped the leads off at the body.

Bugger !

Missed opportunity to share something so uncommon with others. 

[bd139]

I’ll have to buy more scopes to see if I can reproduce it again

[Specmaster]

Maybe time to get on the M4 then http://www.ebay.co.uk/itm/TEKTRONIX-475-ANALOG-OSCILLOSCOPE-ANALOGUE-2x-200MHz-D264/292298225053 Might be good as aprts mule if nothing else?

[bd139]

Already on that one

[tggzzz]

Maybe time to get on the M4 then http://www.ebay.co.uk/itm/TEKTRONIX-475-ANALOG-OSCILLOSCOPE-ANALOGUE-2x-200MHz-D264/292298225053 Might be good as aprts mule if nothing else?

Looks as if it has been damp, and one of the other traditional "exposed knob" problems is present; see the A-trigger knob. It is significant that an electronics recycling company hasn't even turned it on.

Sounds like you are going to be in the never-ending cycle of getting scope N+1 to repair scope N

[bd139]

Been there already. Just joining the cycle again.

About 3 years ago I ended up with 5x Tektronix 465B's dotted around the house. As long as I don't get that bad again, all is good

[Specmaster]

Maybe time to get on the M4 then http://www.ebay.co.uk/itm/TEKTRONIX-475-ANALOG-OSCILLOSCOPE-ANALOGUE-2x-200MHz-D264/292298225053 Might be good as aprts mule if nothing else?

Looks as if it has been damp, and one of the other traditional "exposed knob" problems is present; see the A-trigger knob. It is significant that an electronics recycling company hasn't even turned it on.

Sounds like you are going to be in the never-ending cycle of getting scope N+1 to repair scope N

I'm not sure what it is that you mean, is that one below the power button?

[tggzzz]

Maybe time to get on the M4 then http://www.ebay.co.uk/itm/TEKTRONIX-475-ANALOG-OSCILLOSCOPE-ANALOGUE-2x-200MHz-D264/292298225053 Might be good as aprts mule if nothing else?

Looks as if it has been damp, and one of the other traditional "exposed knob" problems is present; see the A-trigger knob. It is significant that an electronics recycling company hasn't even turned it on.

Sounds like you are going to be in the never-ending cycle of getting scope N+1 to repair scope N

I'm not sure what it is that you mean, is that one below the power button?

Yes. The B-trigger knob in the top right is even more exposed; I've had to replace those in the past.

[Specmaster]

What makes you think its been damp then?