Tektronix 475 blanking problem

Or

snipped-for-privacy@hotmail.com (Andrej Nussdorfer) wrote in news: snipped-for-privacy@posting.google.com:

First,check/adjust CRT bias. That may be all that's needed. Check for proper Z-axis waveform. Then check sweep unblanking gate signal.(real fun,475 has 3 separate sweep generators.)*Read the circuit description in the manual!* (real TEK manual) Last,check DC restorer diodes with a curve tracer,or replace.They break down under HV,so using a DMM check usually will not find bad diodes. Lastly,it could be a G-K short,although that's unusual.

As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep generators (BTW. Jim, I only found referenced in the manual two: fast and slow sweepgen, but these 2x for each A and B sweep - did I miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats section

In mine (ser# 700530) one decoup. resistor in the +15V was burned due to short in nearby tantalum cap (looks like this is often happening - it's the 28th repair case I've like this) and a bad Tran (Q 1044).

The scope is now doing fine :)

hth, Andreas

As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep generators (BTW. Jim, I only found referenced in the manual two: fast and slow sweepgen, but these 2x for each A and B sweep - did I miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats section

In mine (ser# 700530) one decoup. resistor in the +15V was burned due to short in nearby tantalum cap (looks like this is often happening - it's the 28th repair case I've like this) and a bad Tran (Q 1044).

The scope is now doing fine :)

hth, Andreas

PS: sorry for the term debugging..

snipped-for-privacy@bigfoot.com (TekMan) wrote in news: snipped-for-privacy@posting.google.com:

The third sweep gen is for delayed sweep functions,if I recall correctly. I used yellow hi-lighter to hilight the sweep gens in the manual I used when I was with TEK.It and a chart in the circuit descriptions(IIRC) were valuable in figuring out which circuit was in use when a problem occurred.

Jeez! I bought on ebay a 475 serv. manual, section in the sweep gen schematics highlighted with yellow text marker. Maybe might be preowned by you. I wonder how it made the long way to Europe.

Yes, the chart in the circuit descriptions is real helpful. Speeded up the repair a lot.

Andreas

snipped-for-privacy@bigfoot.com (TekMan) wrote in news: snipped-for-privacy@posting.google.com:

Mine will have voltages,notes and part numbers written on the schematics.Might even have my name on the inner cover. I'm pretty sure it went into the dumpster when we moved to a new location,though.

You guys would puke at the number of TEK manuals I've seen thrown into the dumpsters after several moves.If I had a place to store them,I might have kept them. AACK,the stuff I could have saved!

Hi everybody!

Thanks for all the answers! they will be quite helpfull. In the meantime I discovered another suspicious thing. Three diode rectifiers (CR1442 +15V unreg, CR1452 - +5V unreg and CR1462 - -8V) are extremely hot. Actualy too hot to touch. Has anybody else noticed something like that?

Thank you again!

Andrej Nussdorfer