Oscilloscope help

[Eastham]

I bought my first Oscilloscope today for £33! It's a Gould OS 4000, on channel 2 I can get a sine but channel 1 is completely dead, probing around with my meter I found that the collector voltage on TR307 on the pre-amp board is low at 1v, it should be at 5.8v, if anyone could help me trace out the schematic I'd be very great full as I'm still kinda crap at reading schematics. Thanks.

 

[Alan0354]

You bought it new? Don't do anything if it is under warranty. You need to post the schematic.

 

[Eastham]

Nope, used.

 

[nj pheonix]

£33?
Forgive my ignorance.
That would be 33 British pounds?
Did i come with the understanding that it was completely functional?

 

[Eastham]

Yep, pounds, it came as powering on but "unable to test further".

 

[petehall347]

http://www.vintage-radio.net/forum/showthread.php?t=51478

 

[Eastham]

Thanks for the link Pete, just looked at R751 is burnt pretty badly, guess I'll look around in my part's drawers see if I have any 22ohm resistors laying about, makes me wonder what caused it to light up in the first place though. ghetto rigged a test lead using an allen key and a crocodile clip lead, got some nice probes on the way.

 

[Eastham]

Welp my scope leads came today, so I decided to test the output power of my Yammie, 20.8v or 54 watts at 1KHz, not bad considering it's rated for 35WPC, I just experimented with that resistor jumping it with my multimeter set to mA and I got a trace from channel 1, new 22ohm resistors should be here tomorrow, I'm so happy especially after playing with it all day.

 

[for_p1]

Yep, pounds, it came as powering on but "unable to test further".

Unfortunately you wasted these 33 pounds. When you buy measurement devices, you should trust them 100%. Otherwise they serve no purpose. If you need scope, get Rigol 1054z from China - you will not be disappointed.

 

[Eastham]

I'd love to buy a bran new 'scope like that but my hobby is stuck to a tight budget, a family member is coming to visit from Scotland he used to do alignments on test gear as his job so he said he's gonna bring some equipment with him and help me make sure everything's working within spec.

 

[BinaryMike]

Good show! For people with an interest in electronics, getting a scope is like removing a blindfold. If you can pick up a function generator or sine/square audio generator, then you have the tools to teach yourself all the basics of analog electronics.

 

[Eastham]

Good show! For people with an interest in electronics, getting a scope is like removing a blindfold. If you can pick up a function generator or sine/square audio generator, then you have the tools to teach yourself all the basics of analog electronics.

No kidding, I'm sure this 'scope is going to serve me well. I've already used it to fix my Sansui 310 "Shed receiver" which was distorting the right channel heavily at half volume. A function gen is next on my list, my PC will suffice for now but a legit piece of tech would be nice, slowly building my lab!
The 22ohm resistors came today, I was originally going to hack one in by tacking it to the leads of the old resistor I cut out because I didn't want to remove the CRT. Well I decided I couldn't live with myself doing that so I discharged the fly back with a screwdriver and a alligator clip lead, two screws let you pull the CRT back, up and gently rest it out the way and then you have access to the other side of the A.D.C board.



Danger? High Voltage!? Why, that's the best kind of danger!



Gentle don't break the CRT wires...



Annndddd WORKING! all the voltages are fine, current draw across the resistor seems fine, pretty stoked, just need my uncle to do a "quick alignment" on it for me and I'll be good to go!

 

[ghazzer]

Mike: What do you think about a small SS signal generator like this: http://www.ebay.com/itm/321210132360?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT ?

It only outputs ~9V p-p, but that has not been a problem, so far. I would have gotten one with more capabilities, but I don't use it often. I have been pleased with its performance, but I do remember that 'ignorance is bliss'.

Nice work Eastham! Repairing your gear is a significant accomplishment, and a morale booster.

Enjoy - - -

 

[Eastham]

Well guy's, looks like Murphy has come and bit my bottom, I had the scope idling with no probes attached both channel traces on the screen just running to test my repair and everything was going great then suddenly the display just went blank, no traces, everything was still powered up and working, the CRT just went blank, I've checked all of the voltages and even my repair all fine and within spec, I can hear something rattling around inside the CRT, I think it just blew...

 

[petehall347]

what tube does it use ?

 

[Eastham]

A D14/180GH, it's glass that's rattling inside it so I guess it's lost it's vacuum.

 

[Eastham]

I've gotten it to do something, it's now displaying something again just a dot and the heater is definitely working.

 

[BinaryMike]

Mike: What do you think about a small SS signal generator like this: http://www.ebay.com/itm/321210132360?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT ?

I would be strongly tempted to give it a shot if my budget was constrained. Sinewave distortion is pretty high, and I didn't see any evidence that it has an output level control, but that's a fairly easy thing to add if necessary. What I had in mind was something more like this, with quoted sinewave distortion of -55dB max (<0.18%) in the audio spectrum. That's good enough for rough amplifier distortion measurement purposes, which may be important to folks here at AK.

 

[BinaryMike]

A D14/180GH, it's glass that's rattling inside it so I guess it's lost it's vacuum.

It's not terribly unusual to discover loose particles inside big tubes. They won't necessarily cause trouble unless they scrape phosphor off the screen or come to rest in a critical location. Your symptoms suggest failure of one or more power supply rails instead.

 

[Eastham]

That's what I initially thought, but all the voltages are there, and I seem to be getting high voltage though I have no true means to test it.