Very Inexpensive 7623A, but Problems


 

I bought a very inexpensive 7623A on the auction site and it just arrived. The aluminum cover on the back was dented in, and there was some damage to the low voltage regulator board (the fuse was shattered and one ceramic capacitor was cracked). I replaced the fuse with the lowest amperage fuse I had (0.5A, but what was required was 0.15A, I've got the correct fuses, and replacement capacitor on order from Mouser), just so I could see if it would power up.

It does power up, but the image that appears on the screen is badly distorted, and does not seem to respond to horizontal of vertical position controls. I have put a picture in the following album: https://groups.io/g/TekScopes/album?id=260677

Any opinions on how boned I am? Is this fixable, or am I looking at a CRT replacement?

-- Jeff Dutky


Bob Albert
 

Off the top of my head I would guess the CRT is toast.  I worked on a Leader scope with a somewhat similarly distorted display and there also I felt something awful had happened to the deflection plates.  Perhaps the unit has been dropped.
Bob

On Friday, February 12, 2021, 10:14:17 PM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:

I bought a very inexpensive 7623A on the auction site and it just arrived. The aluminum cover on the back was dented in, and there was some damage to the low voltage regulator board (the fuse was shattered and one ceramic capacitor was cracked). I replaced the fuse with the lowest amperage fuse I had (0.5A, but what was required was 0.15A, I've got the correct fuses, and replacement capacitor on order from Mouser), just so I could see if it would power up.

It does power up, but the image that appears on the screen is badly distorted, and does not seem to respond to horizontal of vertical position controls. I have put a picture in the following album: https://groups.io/g/TekScopes/album?id=260677

Any opinions on how boned I am? Is this fixable, or am I looking at a CRT replacement?

-- Jeff Dutky


Tom Lee
 

The readout seems basically ok, so the CRT is being deflected properly both horizontally and vertically. Were the plug-ins part of the unit, or are they known good ones from your collection?

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/12/2021 22:13, Jeff Dutky wrote:
I bought a very inexpensive 7623A on the auction site and it just arrived. The aluminum cover on the back was dented in, and there was some damage to the low voltage regulator board (the fuse was shattered and one ceramic capacitor was cracked). I replaced the fuse with the lowest amperage fuse I had (0.5A, but what was required was 0.15A, I've got the correct fuses, and replacement capacitor on order from Mouser), just so I could see if it would power up.

It does power up, but the image that appears on the screen is badly distorted, and does not seem to respond to horizontal of vertical position controls. I have put a picture in the following album: https://groups.io/g/TekScopes/album?id=260677

Any opinions on how boned I am? Is this fixable, or am I looking at a CRT replacement?

-- Jeff Dutky




 

The plug-ins came with the unit, and they all have some damage, especially the horizontal plug-in, whose TIME/DIV knob is badly bent (is that visible in the picture?). So, no, the plugins are NOT "known good".

This scope comprises the entirety of my 7000-series collection.

Also, I was wrong about the traces not responding to controls: I can get those wiggly radial traces to shimmy a little bit by adjusting the horizontal position knob.

The plug-ins, aside from the knob damage, appeared good to a cursory inspection (I gave the scope a once over before I plugged her in. I'm fool hardy, but I'm not completely reckless).

I would be very happy if the problem were just the plug-ins.

I'm waiting on the replacement fuse and capacitor (though, I guess they're not strictly necessary).

I tried connecting a probe and seeing if I could get any kind of trace from the calibration signals, but got nothing. Then I put the probe back on the scope it came from, and checked the 7623A's calibration signals and they look kind of wonky: the 2236 couldn't get a stable trace on them (I'll put pictures in the album).

Clearly this is a sick little scope. What fun!

-- Jeff Dutky


Tom Lee
 

Ok, so you have several possible points of failure, then. That makes troubleshooting extra fun.

Out of curiosity, does the readout properly reflect the states of the corresponding plug-ins' settings?

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/12/2021 22:50, Jeff Dutky wrote:
The plug-ins came with the unit, and they all have some damage, especially the horizontal plug-in, whose TIME/DIV knob is badly bent (is that visible in the picture?). So, no, the plugins are NOT "known good".

This scope comprises the entirety of my 7000-series collection.

Also, I was wrong about the traces not responding to controls: I can get those wiggly radial traces to shimmy a little bit by adjusting the horizontal position knob.

The plug-ins, aside from the knob damage, appeared good to a cursory inspection (I gave the scope a once over before I plugged her in. I'm fool hardy, but I'm not completely reckless).

I would be very happy if the problem were just the plug-ins.

I'm waiting on the replacement fuse and capacitor (though, I guess they're not strictly necessary).

I tried connecting a probe and seeing if I could get any kind of trace from the calibration signals, but got nothing. Then I put the probe back on the scope it came from, and checked the 7623A's calibration signals and they look kind of wonky: the 2236 couldn't get a stable trace on them (I'll put pictures in the album).

Clearly this is a sick little scope. What fun!

-- Jeff Dutky




Stephen Bell
 

The CRT can't be all that bad given that the readout is displaying recognizable albeit blurry characters.

Can you improve the focus of the characters? Try turning the brightness down a little to see if that improves the focus.

The traces of the calibrator waveform would seem to indicate a problem with the timebase module. The time/div knob looks bent and it could be stuck in the mixed timebase mode which might give the display you are seeing.Try pushing the time/div knob into disengage mixed mode sweep.

Do you have another timebase plug-in you could substitute to verify whether the timebase module is faulty?


 

Tom,

Extra fun indeed.

Yes, the readouts do appear to reflect the control settings. Parts of the readouts come and go in unpredictable ways, however, and this intermittence is affected by vigorously wiggling the main knobs on the plugins, but not apparently by tapping or knocking on the case, which I take to imply that the malfunction is not due to something loose in the CRT, but may be confined to the plugins. (EDIT: it's NOT confined to the plugins, the radiating twisted traces are still there with all plug-ins removed)

Stephen,

Yes, the timebase has been sorely abused and the main knob is bent out at about a 15 degree angle. I am able to take the timebase into and out of mixed mode, but I fear that there is some internal damage from the force that bent the knob. It looks like the outer shaft that is engaged by the large knob, has sheered off, and the outer knob is jammed in a position that prevents me from removing the cal knob.

I have ordered an entire new timebase plug-in, but it will be a week or so before it arrives. I'm just assuming that the timebase is borked, and a replacement was pretty inexpensive.

I tried powering the mainframe without the plug-ins, and I still have the twisted radiating lines. Only the readout intensity knob has any effect on the display. I tried working the storage controls but couldn't get anything recognizable to happen.

I guess I should begin at the beginning: take off the sides of the case, do a full visual inspection, and then check the power supply levels. That's probably the best I can do until the new horizontal plug-in arrives.

-- Jeff Dutky


Jean-Paul
 

Jeff definitely check PSU and HVPS/CRT voltages first, also check for loose or disconnected CRT deflection leads.

You can run these with Vert modules in the Hor socket, for testing.

With no plugin in the H position you will get a vertical line and visa versa.

With no plugins at all just a single spot, centered and undeflected (keep intensity low)

Kind Regards,

Jon


 

The readout looks correct, so I think the CRT is probably OK.

D.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff Dutky
Sent: 13 February 2021 06:14
To: TekScopes@groups.io
Subject: [TekScopes] Very Inexpensive 7623A, but Problems


am I looking at a CRT replacement?


 

Jean-Paul,

I've had a little fun swapping the plug-ins around, but it hasn't made much difference in the display (it's made some difference, but I'm still not getting anything like real horizontal or vertical deflection). The twisted radiating lines are a constant feature, no matter which slots which plug-ins are in, or even if there are no plug-ins installed. Those lines only respond to the readout intensity control, the main intensity control seems to have not effect at all.

David,

Thanks for chiming in; every reassurance that I don't have a busted CRT raises my spirits. I was really excited to have an analog storage scope to play with, and I had been holding off because I was scared that either a lot of scopes I saw on the auction site seemed to have malfunctioning CRTs (or the people taking the pictures had no idea how to set the intensity properly), or that a good CRT would arrive demolished in transport (that happened to one scope, already).

I'm going to do a full visual inspection of the mainframe, and then check all the power rails, but not tonight. I need all my wits about me for an operation like that.

-- Jeff Dutky


 

I came across this video (https://youtu.be/H-9YdqiptDM?t=1013) and it shows something that looks very much like what I am seeing. The caption, just before it shows the radiating twisting traces says "This is how it looks with the defective capacitor inside..."

This fills me with hope.

-- Jeff Dutky


Eric
 

Take LOTS of pictures. The harmonica connectors have many different voltages on them as low as 5.5 to as high as 130. I quicky turned a 7603 in to a parts unit one when I switched 2 of them. Sent 130Vdc to all the wrong places. Ended up with too much damage to save it so now I at least have a spare CRT.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff Dutky
Sent: Saturday, February 13, 2021 6:34 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Very Inexpensive 7623A, but Problems

I came across this video (https://youtu.be/H-9YdqiptDM?t=1013) and it shows something that looks very much like what I am seeing. The caption, just before it shows the radiating twisting traces says "This is how it looks with the defective capacitor inside..."

This fills me with hope.

-- Jeff Dutky


Jean-Paul
 

Jeff beware:

The "harmonica" multipin ribbons have a plastic that deteriorates and easily breaks when removing or inserting the connectors onto the PCB pins.

The polarization marks are not very obvious.

We use a painter tape to mark connector polarity and J number before touching them.

Finally, may we know what you paid cost + shipping? Just out of curiosity.

Bon Chance,

Jon


Michael W. Lynch
 

I have a 7623A that initially had some issues related to those notorious TI IC sockets. Several IC's were loose or partially seated when it arrived. Since yours has been treated to rough handling, anything is possible. Just something else to verify if yours is equipped with socketed ICs.

--
Michael Lynch
Dardanelle, AR


 

Jean-Paul,

Thank you for the warning.

I paid $60+$35 shipping. It's not quite peanuts, but it's also not quite dinner out with the family.

Eric,

I will be taking lots of pictures.

Michael,

There are lots of socketed ICs (and transistors) to be sure. I will check those after I've done my visual inspection and read the manual a bit (there's lots of warnings, printed on the frame it RED LETTERS, about high voltages. This is an entirely different beast than my 475s and 2200s).

-- Jeff Dutky


Eric
 

Jeff

If yours is a storage scope the HV is really in the HV supply and on the storage board as far as I know. The main 7000 series goes up to a 130 V supply but there is a -4Kv supply for the tube which if I remember correctly is fed in to a voltage tippler which will give you an acceleration voltage of about 12Kv on the fat red wire. Not a tone of current there but it is still jumpy and nothing to mess with. My storage experience is limited to the 577 curve tacers but in there the storage flood guns get a 300 ish volt supply and the deflection plates are driven by 200 odd volts. I do recall that in one of my 7603's there was a bad driver transistor in the LV supply for the pass element. This caused my 130V rail to be off in the weeds at about 149V all because the pass transistor was not being told what to do. There are a couple of power supply design changes the very original 7603's were fan less and had a plastic cover. The metal ones I think have the fan.

Good luck with the restoration.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff Dutky
Sent: Saturday, February 13, 2021 1:33 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Very Inexpensive 7623A, but Problems

Jean-Paul,

Thank you for the warning.

I paid $60+$35 shipping. It's not quite peanuts, but it's also not quite dinner out with the family.

Eric,

I will be taking lots of pictures.

Michael,

There are lots of socketed ICs (and transistors) to be sure. I will check those after I've done my visual inspection and read the manual a bit (there's lots of warnings, printed on the frame it RED LETTERS, about high voltages. This is an entirely different beast than my 475s and 2200s).

-- Jeff Dutky


 

Eric,

Wow! It's a good thing I got myself a brand new HV probe for Christmas (rated to 40KV)! And here I was jumpy about the 2.5KV on the 475! Good times.

-- Jeff Dutky


 

Jean-Paul,

I also splashed out $18 for replacement knobs for the vertical plug-ins (they look the same as the trigger slope knobs on the 475/A, but their inner diameter is different), $50 for a replacement 7B53A, and a couple dollars for fuses and capacitors from Mouser. I'm sure that there will be another Mouser order, once I've figured out what's causing the display misbehavior, but I'm betting it won't total more than $30.

If I get a working 7623A out of this for less than $200 I'll call that a bargain.

-- Jeff Dutky


 

Other minutia:

The serial number is B183764.

The date codes on the ICs range between 77 and 78, so this scope looks like it's about 42 years old.


Eric
 

The good news is you check pre trippler not post so you only need to measure -4Kv. If you have any image it is safe to assume the trippler is working.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff Dutky
Sent: Saturday, February 13, 2021 2:22 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Very Inexpensive 7623A, but Problems

Eric,

Wow! It's a good thing I got myself a brand new HV probe for Christmas (rated to 40KV)! And here I was jumpy about the 2.5KV on the 475! Good times.

-- Jeff Dutky