Manual for a late-revision HP 141T? (SN 2233- or higher) [Solved] - Page 1
Forum section: electronics / repair

author: JLNY
author_rank: Regular Contributor
timestamp: July 09, 2017, 09:56:52 pm
content: All,I was recently doing some work on a HP 141T spectrum analyzer, and while I was debugging it the display started gradually flickering and jittering. (see my thread here about trying to fix a 8553 plugin:https://www.eevblog.com/forum/repair/blown-input-on-hp-8553b-sa/)Looking at the power supply, all of the rails are reading low. The 141T uses a series regulated PSU that uses a +100V rail as its master reference, so I suspect that something on the +100V rail is starting to fail.I have already tried swapping out the Q2 power transistor-- no change. I also tried connecting another capacitor in parallel with the C3 filtering cap, no change. I tried swapping the plugins out for a set of known good plugins, no change. so I do not believe there is any fault with the plugins, and I am guessing that the fault is after the regulator transistor?Normally, this wouldn't be the first time that I have debugged power supply issues on a 141T, but the issue here is that this is an unusually late revision 141T (SN 2233-, so mid-1982), but the only manuals I can find online only cover up to 1977. It seems that sometime in between these dates they revamped the power supply board so that it doesn't use a neon regulator as the voltage reference, and eliminates the 10V oscilloscope calibrator rail. It has a completely different board layout from any of the manuals I have been able to find. a lot of the resistor values look to be different as well.Another quirk of these late 141Ts is that they have a protection relay mounted above the CRT that prevents the unit from powering up without any plugins in, which is actually a bit frustrating given that I would prefer not to risk the safety of my plugins while working on the power supply. I have seen one other 141T from 1985 and it also had this feature.Does anyone know where I could find a manual that would cover this unit? Ideally, I would even like to find a manual to cover my 1985 141T (SN 2506-), but the power supply board looks to be largely unchanged from the 2233- unit.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 09, 2017, 11:38:09 pm
content: Have you gone through the sites listed here?https://www.eevblog.com/forum/repair/repair-documents-and-links-sticky-me-please-mods/Ed

author: JLNY
author_rank: Regular Contributor
timestamp: July 10, 2017, 01:34:56 am
content: Yes, I have gone through many of those sites, but it seems nearly all of them are copies of the same few scans from about 1976 and 1977.Fortunately, I asked around with a few eBay manual sellers, and it turns out that Artek Media's scan covers SN 2205, so hopefully it will have the later power supply revision I need. fingers crossed.

author: alm
author_rank: Super Contributor
timestamp: July 10, 2017, 01:41:27 am
content: Depending on the extent of the changes, all you may need is the change notice pages that would be added to the back of later printings. But if Dave says he has the correct version, then that should serve you fine. If it does not, then you should at least easily get a refund from him.

author: JLNY
author_rank: Regular Contributor
timestamp: July 10, 2017, 02:01:21 am
content: From comparing my unit to the 1977 manual, it seems like they did some re-working on the power supply to eliminate the specialized A2V1 neon lamp regulator that they were using as a voltage reference for the +100V rail, and possibly a few other things. The changes to the board on this later revision board look to have eliminated and/or moved a few things around, so I'm having trouble locating some of the components, and some of the component values look to have changed as well.I exchanged a couple messages with Dave from Artek on eBay. He said that his scan does not have the V1 neon lamp regulator that the 1976/7 scans show. It seems like he had looked at the schematics and knew what he was talking about on the technical side, so I'm optimistic that the manual will work.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 11, 2017, 12:38:28 pm
content: JLNY,I've just uploaded the HP manual changes supplement that covers 141T S/N prefixes 1850A, 2020A and 2101A, to KO4BB's manual site. It's currently under Recent Uploads, until review.This change notice does indeed show the newer zener-referenced 100 Volt power supply. As the file is a mere 827 kB, I've attached it to this message.Glad to be of assistance,RF+ Tech

author: JLNY
author_rank: Regular Contributor
timestamp: July 13, 2017, 11:28:13 pm
content: Found the fault in one try.The CD with the Artek manual arrived today. I took a guess that the fault might be from a leaky C4 capacitor. I tried replacing it, and, in line with my initial suspicions, it immediately started working again.It is worth noting that C4 is a different value, connected differently, and in a completely different location on the newer board revision, hence why I was having trouble finding it earlier. Also, a lot of the other values and components have been changed around, especially on the +100V rail. Having the right manual revision made a big difference here.With the capacitor replaced, the flickering is gone and all rails are reading the correct voltages.That said, it looks like the trace rotation and geometry adjustments are a bit off, so I'll probably go in and tweak it a bit before closing it up.Also, sorry I didn't see your reply sooner RF+Tech! That schematic seems to match up with the newer board revision, so thanks for posting it. Hopefully that can help out anyone else doing work on their 141Ts, although I will give Dave credit and say that the Artek manual is a pretty good quality scan if you want to spend the extra few bucks to buy the CD.

author: alm
author_rank: Super Contributor
timestamp: July 13, 2017, 11:30:12 pm
content: Or just buy directly fromhttp://artekmanuals.com/and get the download link in a couple of hours after payment.