Gould/ Advance OS3000A/ PO Oscilloscope 16A

[ChristianFletcher]

Hello Tim

I thought you did some great work fault finding and repairing the scope. The problem is once you have one they seem to attract one another. I have 12. Oops it’s 13 now I bought another one today a PM3127. I was looking for a valve scope for working on valve gear but it didn’t work out like that today.

Regards Chris

[Tim]

Hi Christian.
Fear not, the saga continues! Another fault has manifest!
After a few minutes the trace height deduces and y shift range (up and down) is much reduced.
Since it happens on both channels I'll be concentrating on the beam switching and Y amp.

[Tim]

Bummer. Found the emitter lead has broken off one of the y output transistors right at the body. BD529 I think. A replacement, but not a bad choice.
It must have been intermittent at the very least. Both traces blurred and at the top of the screen at the moment until I can find another transistor. Not sure if the reduced trace height and vertical shift( both channels) was caused by it or not. I don't think so as my effect is/was
quite symmetrical.

[Tim]

Well, I found what was causing the fault. A stray washer lodged under the other Y output transistor leads. I don't think it was me, as everything went back together and (believe it or not) I had no screws/washers missing. I can only suppose it must have been dropped into the works by a previous repairer, but may not have caused any trouble until I started fiddling with it!

I have found a BF336 & heatsink that I might try as a temporary replacement, but I reckon a pair of MPSA42's might do the job very nicely, as BD529's do seem to be rather pricey.

[Tim]

Oh dear. The washer wasn’t it. Despite performing well for a six hour test( the fault came on much before that) it’s now back.
Reduced trace height on both channels irrespective of channel mode, and reduced Y shift evenly at top and bottom. Y *5 seems to work, and a large input signal will clip at limits of deflection. S2 is high at about 60 volts( quoted as “ about 40” but is the same whether the fault is present or not.
Stay tuned for the next thrilling(?) intallment!

[Tim]

Solved!
Sort of.
I found the problem, but haven't fixed it as yet. All the reduced y amplitude and shift problems seem to have been caused by an intermittent short at the input of one of the delay lines. I think it was actually just inside the plastic core(dilectric?) as the wire broke off when I was trying to slide some sleeving onto it to cure the intermittent short.
Too frazzled and my eyes are too tired to focus on it tonight.
Unfortunately Mrs. T is always of the opinion that there are much more important things to be doing than silly Oscilloscopes, so I don't get much time all told to deal with it, being limited to when she is out( and I'm in) or in bed.
I still have to match up some BSW68A's for the "Y" plate output, deal with the delay line then calibrate the Y section/s as the deflection is slightly low/insufficient by the same amount on both channels, although it may well be OK once I have fixed the delay line issue.
Not sure when I'm going to be able to fit all this in, so this particular repair adventure will be paused for the time being.
Fortunately I do have a Philips PM3240 which should help to ameliorate my 'scopelessness.

[Tim]

This is the last one, honest!
Well it’s finally done, and seems to be working and stable.
The delay line that was giving some trouble was stripped back and re terminated, and both the Y output transistors have been replaced. I was going to mount a couple of BF257’s on a bit of Vero, far enough apart to accommodate some clip on heatsinks. As it was I was short of time( I can only do it when SHMBO is out) so ended up mounting a pair of BSW68a’s direct onto the pcb pillars and fitting some corrugated heatsinks. They run just too hot to hold a finger on, but seem to work OK.
Took a risk and left it on overnight and still working the next morning.

Just for a bit of fun, can anyone work out what frequency I am displaying, given that the timebase seems to be spot on accurate.

[Argus25]

Originally Posted by Tim

I'm going long sighted, which is rather inconvenient for close up work, as I have difficulty focussing in poor light. Arms length and distance, such as driving is fine, but I'll have to get it sorted or soon my arms won't be long enough.

You are not going "long sighted" you are simply becoming increasingly Presbyopic, which is normal at your age. It is not indicative of an eye disease.

Some glasses for near work would help you. You could use some ready made types around +1.5 D normally fine initially and if you want to hold objects closer and have more magnification, use +2D or higher.

It is better though to go to an Optometrist to get them, because you get an eye examination which can detect diseases, which sadly many people miss out on if they just use the ready made glasses from the shops.

Some eye diseases, especially Glaucoma, are asymptomatic, that is until it is very severe. So better detected early with an eye examination and treated early too.

[Tim]

Thank Argus. I have something to Google.