HP 3580A audio spectrum analyzer (long)

[Wirecutter]

This is a question for anyone that has the HP3580A spectrum analyzer and the manual for it.  I have the PDF version of the manual, which unfortunately is an image scan of all the pages.  That means it is not searchable.  Gaaah.  Ok, rant mode off.
My 3580A isn't working yet.  I'm trying to get there.  The -10v and the -11.5 seem to be okay, but the +10 and +11.5 are low.  I'm troubleshooting the A6 board, which is the low voltage power supply board.  At some point, I desoldered all of the transistors on the board and tested them with my cheap DMM.  The board has 2 kinds of TO-66 transistors - 2 NPN and 2 PNP, and 2 kinds of TO-18 parts - again NPN and  PNP.  When I tested the TO-18 parts, I removed all the PNPs, tested, then reinstalled.  Then repeat with the NPN parts.  This was so I wouldn't mix them up.
Page 7-31 (or pg 187 of the pdf) shows the layout of the A6 board. Q20 is shown near the upper left of the page, and the orientation tab is shown to be at about 7 o'clock. That would have the leads positioned so:
   C
B
   E
I traced the circuit, and that would have the emitter going to R37, but in fact, the collector is supposed to go to R37.  I think the orientation tab of Q20 on page 187 should be at 2 o'clock.
I know it's asking a lot, but can any of you HP3580A users or maintainers verify this?  Thanks.
-M

[Messtechniker]

There are things like image to text converters (OCR) even for free......

[factory]

How low are the voltages? Did you check the voltage setting/feedback resistors, these often drift high in older HP scope power supplies.
What part number is the transistor? Some of the house coded parts were from multiple sources and could be different lead pinouts, the leads are usually formed to have base in the middle on the PCB.

David

[Wirecutter]

When I tested the transistors on the A6 board, I didn't keep track of exactly which one went where - I just made sure to remove all of a specific part, test them, and put them back.  Then on to the next specific part.  I also briefly powered the board with the previously mentioned Q20 oriented as shown on page 7-31 (187 of the pdf).  I have since corrected the orientation of Q20 after tracing the circuit, as mentioned in my previous post.
The new symptom is that the +11.5V at F1 is reading correctly, but the -11.5V at F2 is reading about -6.5V, with a current of 550mA.  That is obviously overloaded, since the fuse rating is 500mA.  I think if I left it powered long enough, the fuse would have to be replaced.

I keep checking that the 2 fuses are not blown, and so far, they're both okay.  I'm going to disconnect J1 from the control board to disable the high voltage.  If that causes the -11.5V to read correctly, then I'll have to take a careful look at the HV.

[Kwakerman]

Hi, As it happens I've actually got two 3580A's on the bench at the moment (and an original manual)!  There are two versions of the A6 (early and late) and I've got one of each.

The position of Q20 tab is different depending on what version PCB you have (see my  posts below), I think you may be looking at wrong version diagrams.

As part of my faultfinding I measured the voltages over the 1 ohm current sense resistors on the + and - 10 v supplies.  The +10 measured 0.45V (= 450mA) and the -10 measured 0.2V (=200mA).

Would a descent picture of the component side of the PCB (both types) help you?

[Kwakerman]

Early and Late types (main difference are two TO-220 devices on heatsink), I've set them large to help you zoom in but may need to do it in two posts due to file limit restrictions!

[Kwakerman]

Late style

[Kwakerman]

Let me know what version you have and I'll try and take a clear picture of the service manual.  The late version is the first one in the manual, if you go to the back (end) of the manual (the 'Backdating' section) the early version is in there.

[Wirecutter]

That is a really good photo, thanks.  Looks like I have the late version, because I have the two TO-220 devices on the heatsink.  The relays on my board look a little different, but I'm sure the functionality is the same.  Oh, and Q20 is HP part 1854-0404.  According to the googling I did, that crosses over to a Texas Instr. AST4260.

Another random note:  When I opened the SpecAn up the first time and inspected things, I found that the magic smoke had escaped from C21 on the Low Voltage Power Supply board, and I replaced it.  That's also what led to testing all the transistors.  They all test good, but something's up because the symptoms change when I mix transistors around.  I might do some preemptive replacement of them.

However, I am a dummy on a couple of fronts.  I actually paid for the pdf off of fleabay, then discovered that I already had a free download from when I had a 3580 a few years back.  I have noticed a few discrepancies in the schematic and layout docs.  On the schematic page for the Low Voltage power supply, the TO-220 devices are both labelled Q3.  Actually, the top "U3" is indeed U3, and it's an LM317 voltage regulator.  The bottom "U3" is in fact U4, and it's an LM337 voltage regulator.

What else?  With regards to the labels for the card-edge connectors, it was not obvious to me if the lettered pins were component or solder side and vise versa.  So I traced a few of those, and found that numbered pins were on component side and the lettered pins on solder side.  I don't have adjustment pot R39 on my A13 Deflection Amp board, and my serial number is below the one mentioned, so I guess the note on page 7-28 means I have the A40 board somewhere.

I'm measuring the +/- 11.5V across the output filter caps C1 and C6 on the Low Voltage Power Supply.  If I disconnect J1 on the control board (thus disabling the HV), the -11.5V previously measured at -6.5V will jump to -18.5V.  So something about running the HV seems to be overloading the -11.5V rail.

[Kwakerman]

Good spot with U3, hadn't noticed that but then again I'm currently working on the early version which doesn't have U3 & U4 (but does have a low +10V at 9.6V).

Just let me know if you need any info, my late version A6 is working so can do some comparison measuring on it if you need.

[Wirecutter]

Thanks, Kwakerman.  I'll ask more questions as I come up with some that are not ridiculous.  Fortunately, I have a good soldering/desoldering setup, and I know how to use everything.
I think I'm going to start replacing transistors one at a time and see how symptoms change.