Tek 2235 and Fluke 1952A - Page 1
Forum section: electronics / testgear

author: GreyWoolfe
author_rank: Unknown
timestamp: October 13, 2013, 12:18:14 am
content: I was at a Hamfest today and picked up a couple of toys. The first is a Fluke 1952A that powers on but I can't seem to find a manual online. Could anyone help? The second is a bit more challenging. I picked up a Tek 2235 100 MHz scope. I just powered it on and both channels exhibit the same issue. instead of a trace going horizontally across the screen, there is a vertical line about 4 divisions in height with dots at the top and bottom. Manipulating every button and switch doesn't change anything. Hooking up a probe to get a cal waveform doesn't change anything nor does connecting a signal generator. After a few minutes the display fades out. If I press the beam find, the trace will reappear but disappear when I release the button. My 2 questions are-where to start looking and does anyone have a copy of the service manual? I can find the operator manual but not the service manual. I only paid $40 USD for the scope and $10 USD for the counter so I am not out a lot of money. I would like to try to fix the scope to use with an octopus that I plan to build. I went to ITT Tech back in the late 1990's and ended up working as a field tech repairing computers and printers. Most of what I learned, I have forgotten, but the bug has bitten me again and I want to start relearning. Unless the scope is well and truly hosed, I want to make this my first repair project if possible. I would appreciate any help the great people on this forum can give me.Tom

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 13, 2013, 12:35:12 am
content: Goto K04bb for the manuals:http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_2235There's a service manual (sm) and I think some large format schematics available.The very first thing to check are all of the low voltage levels. A fault on any one of them will severely impact the operation of the scope. I haven't worked on any of the 22xx series, but I think there's a switcher power supply in there. There's also the possibility of a shorted tantalum somewhere.Once you get the manual and get some more info, you might want to check out the yahoo tekscopes group. Lots of tech advice available there.

author: Vgkid
author_rank: Super Contributor
timestamp: October 13, 2013, 02:31:41 am
content: I have a manual for a fluke 1952B, I will try to get it uploaded.

author: GreyWoolfe
author_rank: Unknown
timestamp: October 13, 2013, 04:32:45 am
content: Paul, thanks for your help. I will still need a magnifying glass to view the large scale drawings! Do you know if they are actually larger than 8.5 x 11? I can always go the Office Depot and have them print them out larger. I already checked a couple of marked voltage points. The 8.6VDC was 8.674VDC, the 5VDC was 5.191VDC, the -8.6VDC was -8.591VDC and the +100VDC was 101.71VDC. Now, I can look for test points and all the other low voltage points and see what I can find. VGkid, that would be wonderful if you could upload a copy of the manual.Tom

author: Vgkid
author_rank: Super Contributor
timestamp: October 13, 2013, 07:06:09 am
content: Do you need anything specific(and pronto), it might take me a couple of days.

author: GreyWoolfe
author_rank: Unknown
timestamp: October 13, 2013, 01:37:50 pm
content: Vgkid, there is no rush. I just want the manual to learn how to use it and see if it is fully functioning. Paul, the service manual on KO4BB's site is not actually a service manual but a user manual. The sm stands for small print. I included 2 photos of the screen, the first just with the scope on and the second with the find beam button pressed.

author: GreyWoolfe
author_rank: Unknown
timestamp: October 13, 2013, 02:25:20 pm
content: So far, I found these caps measured open, C975, C976, C979 and C855. These caps are marked TRW-8614 .01uF +/- 20% 3K VDC. I can't seem to source these. I found Panasonic film capacitor, part # ECW-HC3F103JD on Digi-key. Would this be a suitable substitute?

author: GreyWoolfe
author_rank: Unknown
timestamp: October 13, 2013, 02:34:02 pm
content: Let me clarify to make sure that I am doing this right. When I probe these in circuit, my meter reads infinite resistance immediately, there is no build to infinite. Should I be cutting a lead and measuring the resistance? I don't yet have an ESR meter to test the ESR.

author: Unknown
author_rank: Unknown
timestamp: October 13, 2013, 02:55:25 pm
content: Depending on the speed of your DMM, the auto-ranging and the current it uses to measure resistance, 100 nF may very well be too small to measure using this method.Assuming you don't have a meter that measures capacitance, two approaches that come to mind is putting the suspect cap in series with a known-good 100 nF cap, and feeding an AC signal (for example a 60 Hz sine wave) through them. The ACV voltage across both of them should be approximately equal. This uses the cap in a capacitive voltage divider. Another approach would be to put your DMM in DCV mode in series with the unknown cap, and apply a DC voltage (from a power supply or battery) to this circuit, for example 5V. The DMM should initially indicate the full 5V, drop to about 35% of this voltage (1.75 V) in 1s, and to about 0V after a few seconds. This uses the DMM as a 10 Mohm resistor in a series RC circuit (RC time = 1 second). This approach is somewhat similar to the approach used by many DMMs to measure capacitance. Both approaches would require desoldering of the caps.In general you only expect an increase in ESR in electrolytic caps. Film caps rarely fail, but I would expect them to fail either shorted or to decrease in capacitance.

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 13, 2013, 03:31:07 pm
content: Pick the 4th link down on the K04bb 2235 page labeled 2235_sm, it's the full service manual with board layouts, schematics, theory, etc.For large drawings, I blow up the page in a pdf reader, capture the window with an image editor and print it in sections. Then I cut and tape to get a large layout.

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 13, 2013, 06:28:46 pm
content: Those caps are part of the CRT power supply. Since you're seeing something on the screen, it's unlikely those are the problem.

author: markce
author_rank: Regular Contributor
timestamp: October 13, 2013, 09:50:50 pm
content: To support statement made by Paul, it's highly unlikely the 10nF HV caps failed.Don't make any assumptions unless you can measure the HT acc. voltage (special probe).

author: GreyWoolfe
author_rank: Unknown
timestamp: October 14, 2013, 12:01:17 am
content: I am going to take Paul's suggestion and do an expanded print on the schematics. I also am planning to make an octopus component tester. I should be able to test all the caps and diodes in the power circuits with it, am I correct? I will also look at the vertical and horizontal amplifiers and see if there is any failings there. I am in no big hurry to get this working but I will pick at it and post back my findings. I do have my BK Precision 5100 100 MHz combiscope to help and for other learnings. I appreciate all the feedback. It has been VERY long time since last component troubleshooting took place. I can guaranty that I will be asking lots of questions on lots of different topics to help me comprehend better.Tom