Date   

Re: [dead tek 485] Can i fix it ? (newbie here)

Michael W. Lynch
 

On Thu, Jan 28, 2021 at 09:21 AM, satbeginner wrote:


So posting that one would mean I have to scan it first, but I do not have my
scanner connected to a PC, also available time would be an item.
Leo,

I understand your situation. I was just hoping that someone here might already have a later version of these manual sections in their digital archives. I would be glad to scan it, I have the time and the scanner, but not the documents. Unfortunately,we are not exactly neighbors. Perhaps this will turn up eventually? I appreciate your sharing the fact that this newer information exists. Glad you got the chance to give your 485 a "tune up".

--
Michael Lynch
Dardanelle, AR


Re: [dead tek 485] Can i fix it ? (newbie here)

marcosjl31@...
 

On Thu, Jan 28, 2021 at 05:53 AM, Roy Thistle wrote:


On Thu, Jan 28, 2021 at 04:55 AM, Raymond Domp Frank wrote:


what had become clear already in this almost 140 posts-long thread.
well ... Dennis did try to put a cap on long threads, I think ... but, I don't
think people liked it. (I'm not for or against it.)
Some del.V and delxV is almost bound to occur when threads get this long.
Well, as I am the responsible for this ever ending thing, I must first of all apologize for not knowing the rules.
I'm also sorry to be such a newbie in electronics, that's resulting in many errors and wanderings..

But at the very beginning I did be honnest : is this 485 repair and calibration within my reach ? the answers were yes... but I'm not so sure right now.

I can propose to end this thread as first goal was to be able to power on the 485 properly what get done (changing a defective OpAmp)
Now the problems is "intensity adjustement not working" : I can open a new thread on this specific issue if needed .... or make a more radical decision : stop trying to do things that are behind my reach. ;o)

Hope to ear from you.
Jose
(who as already learned many thing from you guys)


Re: Tek 485: Was dead. Was fixed. Clumsy me killed it again. (from a lurker :) ) #photo-notice

Ron Rossi
 

I forget to mention that I have Ohmed out the devices near the crash site...diodes appear good, resistors appear good, caps appear good. So was asking for advice before moving on more broadly.

PS was going to edit my original message, but could not find an edit option. Sorry for the extra post.

73 es God Bless de KK1L, Ron <><


Tek 485: Was dead. Was fixed. Clumsy me killed it again. (from a lurker :) ) #photo-notice

Ron Rossi
 

Folks,
I started following TekScopes a few months ago when searching for hints on fixing my ex-IBM Tek485. I got it working in no small part to hints gleaned from this group. THANKS.

I bring up my mistake to see if one of you all might be able to say "Oh man, yeah. Been there. Done that. The confabulator was fried.", or maybe give a hint where to look first.

After getting it running I figured I would go through the calibration procedure in the manual to see if anything else was funky. I left it out of the chassis to do this figuring I would quite likely be taking it out again. I bet you see where this is going. I was pulling a coax off the A Gate on the back of the scope and the BNC dropped from my fingers landing on the high voltage ceramic stand-off / terminal things at the back of the horizontal board. UGH!! I was so excited to have it working and then in an ignasecond it was taken away.

This is where the BNC bounced off...http://kk1l.com/Tek485_CeramicStandoffTerminals.jpg

Right away the the scope started tick-tunking at a rate just faster than once a second and the beam is quite bright and sweeping from right to left in time to the tick-tunk. Of course I turned it off. Now when I power it on all seems normal for about 5~7 seconds...lights come on, beam builds in brightness...then tick-tunk, tick-tunk.

The inverter fires up, but ripple on the +/-170V rails which was not there before my clumsiness.
http://kk1l.com/170V-TP1835_TriggerOnStart.png (blue trace is 170V at the thermistor and the trigger)

The balance node has a positive 700mV blip.
http://kk1l.com/170V-BalanceNode_TriggerOnStart.png (blue trace is 170V at the thermistor and the trigger)


73 es God Bless de KK1L, Ron <><


Re: [dead tek 485] Can i fix it ? (newbie here)

satbeginner
 

Hi all,

I would love to, but... when I got my 485 (about 5 years ago from an eBay seller from the UK, I got a paper manual in a plastic binder, and a CD with a pdf.
The problem is, the pdf is the 31Mb version that can be found everywhere, and the double sided A4 paper version with the foldout schematics on A2 is that weird Frankenstein version...

So posting that one would mean I have to scan it first, but I do not have my scanner connected to a PC, also available time would be an item.

BTW, the repair Jose is performing led me to opening my 485, only to find it had several noisy potmeters, and also calibration was off.
So (in Dutch: get the cow by the horns, de koe bij de horens gevat) I cleaned the potmeters and performed a calibration, so I'm happy again.

The potmeters who were the noisiest ones, were Ch1 and Ch2 Vertical position, and the Horizontal position, but these are all the square, completely closed versions.

My dirty way of cleaning was: I used a manual 0,8mm hobby drill to make a small hole just next to a corner of that brown little rectangle you can see on one side of the potmeters.
To do that, I only needed to temporarily unscrew the Horizontal Position one, the two Vertical Position ones I could reach and drill while in place.
After that I used the little hole to squirt some cleaner into them.
Quick-and-Dirty, I know, but very, very functional :-)

I added a picture of it here: https://groups.io/g/TekScopes/album?id=259874


Leo


Re: Tek 576

Michael W. Lynch
 

Dirty switches are a common and ongoing problem for these instruments. I have a 577 and 2 576's and they all have a periodic glitch, generally due to a dirty mechanical switch contact. A little cleaning and exercise and they generally come back good as new.


--
Michael Lynch
Dardanelle, AR


Re: Tek 576

Eric
 

I also recommend cleaning the switch first one of my was marked "dead
destroy" there was no trace at all cleaning the invert switched brought it
back and working normally.

Eric

On Thu, Jan 28, 2021, 9:35 AM Michael W. Lynch via groups.io <mlynch003=
yahoo.com@groups.io> wrote:

Those switches typically need to be cleaned. I have used both Deoxit and
IPA, along with some gentle compressed air to clean and dry these.
Exercising the switch while the DEOXIT is "soaking in" also helps loosen
the crud.

--
Michael Lynch
Dardanelle, AR






Re: Tek 576

Michael W. Lynch
 

Those switches typically need to be cleaned. I have used both Deoxit and IPA, along with some gentle compressed air to clean and dry these. Exercising the switch while the DEOXIT is "soaking in" also helps loosen the crud.

--
Michael Lynch
Dardanelle, AR


Tek 7T11A issues

n49ex
 

I'm a new member, but have been an avid Tek scope user/collector/fixer ever since my extensive time using them as a former, now retired Bell Labs engineer.
But my ability to fix has recently been challenged with some problems in my 7S11/7T11A pair:

The 7T11A and 7S11 are situated in my 7904A scope, and the problem I am having with it is that I can’t get a stable trace. In fact, (and I think it is all set up correctly) with a square wave input (from my PG503) I get either a splatter of dots on two lines representing the top and bottom of the signal, but not triggering on a transition, or in some settings just a splatter of dots on the screen. And in some settings, from 50uS on down - non real time, you see nothing at all.

Any suggestions on how to proceed with diagnosis/repair would be appreciated.


Tek 576

lew tyler
 

tek 576 curve tracer #B283924; the screen trace is intermittent when Display (Invert ) switch (467A) is in the released position. In the pressed position, the trace is normal (I am using it
in the pressed (invert) position). the switch is located on the Display Switching Ckt. Bd. (4-29,5-12). Does anyone know of a quick fix/tips to clean/replace this switch???????????
Lew


Re: Tek 465B ch 2 var broken coupler repair

quad@...
 

The 3x3mm flexible couplings from ebay might work too with a bit more needle file work - cheaper.

https://www.ebay.com/itm/162691768380

https://www.ebay.com/itm/323891445851


Re: [dead tek 485] Can i fix it ? (newbie here)

Michael W. Lynch
 

On Thu, Jan 28, 2021 at 07:29 AM, Michael W. Lynch wrote:


This can give a more accurate idea of when the unit was produced.
I meant to include the word "sometimes" in the sentence in the previous post. Using IC date codes is just one way to get a semi-close approximation of the era of the instrument.

--
Michael Lynch
Dardanelle, AR


Re: [dead tek 485] Can i fix it ? (newbie here)

Roy Thistle
 

On Thu, Jan 28, 2021 at 04:55 AM, Raymond Domp Frank wrote:


what had become clear already in this almost 140 posts-long thread.
well ... Dennis did try to put a cap on long threads, I think ... but, I don't think people liked it. (I'm not for or against it.)
Some del.V and delxV is almost bound to occur when threads get this long.


Re: [dead tek 485] Can i fix it ? (newbie here)

Roy Thistle
 

On Thu, Jan 28, 2021 at 05:29 AM, Michael W. Lynch wrote:


That BAMA manual is the older version. I have already downloaded that one. I
would like to have a copy of that "Frankenstein" manual that was mentioned
earlier. It seems to have more modern parts list and possibly revised
schematics included.
Yes... I would like that too. Is it possible to post "Frankenstein" to TekWiki? ... so we can all have a look.


Re: [dead tek 485] Can i fix it ? (newbie here)

Michael W. Lynch
 

On Thu, Jan 28, 2021 at 03:28 AM, <marcosjl31@gmail.com> wrote:


I have a PDF of the User and Service Manual Ref. 070-1193-00 / REV.B March
1976.

I downloaded the PDF from http://bama.edebris.com (link available in the 485
page of tekwiki

Talking of serial number, my 485 has b143403 - probably from 1974/1975 .
Jose,

That BAMA manual is the older version. I have already downloaded that one. I would like to have a copy of that "Frankenstein" manual that was mentioned earlier. It seems to have more modern parts list and possibly revised schematics included.

Regarding your Serial number, that is a "later" serial number. Remember that TEK S/N sequence starts at B010100, so yours is way up the S/N range from there. There were a host of running parts changes made over the 14 year production run of the 485, some components changed multiple times, depending on the serial number of the unit.

Have you looked at the "Date Codes" on the IC's installed in this instrument? This can give a more accurate idea of when the unit was produced.

It is very important to be using the correct schematic and parts list to determine which parts were originally installed in your instrument. If someone has made past repairs using parts that were not applicable to your instrument, then this could lead to a malfunction.

--
Michael Lynch
Dardanelle, AR


Re: [dead tek 485] Can i fix it ? (newbie here)

 

On Thu, Jan 28, 2021 at 06:11 AM, Mark Vincent wrote:


I stated what I have experienced. In no way was I attempting to imply what I
have seen is the only solution. I hope I did not offend anyone by posting what
I experienced or suggested.
Hi Mark,
In threads like these, an effort is made to find solutions to one or more specific problems that someone, usually the OP, experiences with their Tek instrument. If all goes well, efforts converge to one or more probable culprits.
Your recent contribution had a much wider scope, to a large degree foregoing what had become clear already in this almost 140 posts-long thread. That was the reason for my detailed reaction. I admit it's not my role to police threads and I apologize for that aspect of my reaction.

Raymond


Re: 465 - Successfully Replaced HV multiplier

Dave W1BVV
 

Working on the writeup and editing the pics.

Dave, W1BVV


Re: Tek 465B ch 2 var broken coupler repair

Keith
 

And the coupler arrived in the post this morning. It's smaller in outside diameter that the Tek original, which is fine. The inner diameter at 0.125 inch is 2 thou smaller, which meant a few gentle strokes on the shafts with a needle file for it to fit. And fit it does nicely.


Re: Tek 465B ch 2 var broken coupler repair

Keith
 

If this is the flexible coupler, part number 376-0051-00, they are used in many Tektronix instruments. I had one break in a similar fashion on a SG505 oscillator. Tried to glue it and wrap it with heatshrink sleeve, but that didn't hold. The part is basically very flimsy and even a little overtightening will crack the aluminum body.

I have found a brass 0.125 inch flexible coupling made by Huco that looks like it might do the job. The manufacturer will sell direct (https://www.huco.com/shop/couplings/oldham-coupling-1/oldham-coupling-2/500-06), so I've ordered one to see if it's any good.


Re: [dead tek 485] Can i fix it ? (newbie here)

marcosjl31@...
 

On Wed, Jan 27, 2021 at 02:03 AM, satbeginner wrote:


https://groups.io/g/TekScopes/topic/7645269?p= ,,,20,0,0,0::,,,0,0,0,7645269
Leo
interesting thread !
I've been checking the voltages at C1660 and TP1665 when tweaking R1660 pot as per :
"When adjusting R1660 the voltage (call it V1) on C1660 shall go from +80 to +120V. Set the scope in XY mode and adjust the intensity back and forth. The voltage at TP1665 (call it V2) shall go from +10 to +60V (I am now guessing). V1 shall be higher than V2, always."

In my case, V1 goes from +79.95(ok 80V) to 119.22V : this looks correct to me. Let me point out, that I measure the voltage at the capacitor lead connected to R1660...
And if I adjust intensity knob from CCW to CW, voltage at TP1665 goes from ~9V to ~69V

I cannot measure Cathode and grid voltages (> 2900V) as I lack proper tool.

Jose

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