HP/Agilent 6227B Q1, Q2, Q8-Q11 "Not Assigned" in service manual

[scatterandfocus]

I recently picked up a 6227B dual power supply that has one dead side.  The service manual lead me to possible opens in Q8 through Q11, a zener diode, or some resistors.   The service manual says "Not Assigned" for Q1, Q2, Q8-Q11 part numbers.  Anyone know about these parts?

This was an ebay purchase described as, everything working great 100%.  If I can possibly repair it, the seller seems willing to work out a partial refund as if it were sold for parts.  And I would really like to keep it as my first bench power supply.  If not, I guess back it goes.

[scatterandfocus]

A little more info.  These appear to be TO-3 package transistors with this printed on the cans:

4  225
RCA
RY 757540

[Tomorokoshi]

1. Is it the left or right channel that has the problem?

2. Confirm the terminal block strapping as illustrated in section 3-7, Figure 3-2.

3. Are you working through the troubleshooting table 5-3?

4. The Artek copy of the manual is much nicer than the HP (Keysight) scan:
http://artekmanuals.com/manuals/hp-manuals/

5. Fortunately, most of the Master and Slave boards are the same, so with power off, some resistance and diode check measurements can be made to compare between them.

[pbarton]

The 'NOT ASSIGNED' is on the document page 6-7 (or .pdf page 72 of 84).
The next page 6-8 lists Q1 and Q2.
The page after that, 6-9 lists Q8-Q11 and also Q7.

[scatterandfocus]

Thanks pbarton!

I haven't found anyone carrying those part numbers, but I did find this:

https://www.antiqueradios.com/forums/viewtopic.php?t=64420

The series reg. is a little trickier. In this case it is an 1854-0225, and HP provides no cross-reference in the manual. However, if one looks in the manual for the 6214B series, one finds that it is merely a selected 2n3055. Similar tricks work for all of them.

Also something to keep in mind for future searchers:

https://en.wikipedia.org/wiki/2N3055

Counterfeiting

Since the early 2000s, the 2N3055 transistor has been heavily targeted by counterfeiters, who substitute much smaller silicon dies with lesser power ratings, use inferior mounting techniques, and fake the markings. It is by now unlikely to actually obtain a genuine 2N3055 transistor when using popular sales platforms such as Amazon or Ebay; classic electronics distributors are mostly still able to properly source them. [13]

[scatterandfocus]

1. Is it the left or right channel that has the problem?

2. Confirm the terminal block strapping as illustrated in section 3-7, Figure 3-2.

3. Are you working through the troubleshooting table 5-3?

4. The Artek copy of the manual is much nicer than the HP (Keysight) scan:
http://artekmanuals.com/manuals/hp-manuals/

5. Fortunately, most of the Master and Slave boards are the same, so with power off, some resistance and diode check measurements can be made to compare between them.

1. Right (slave side) when the front panel is facing me.

2. The terminal strapping looks good.

3. Yes.

4.  I may pick up a copy of that, but for now I am able to read everything.

When this power supply arrived it had no voltage on one side and a blown fuse on the same side.  I only had a 1.5 amp fuse here (lower rated), so I put that in.  It didn't blow, but I still got no voltage from this side.  I have followed a bit into the service manual so far, up until removing and testing any components.  I'm waiting back to hear from the seller on how much he will knock off the price before I put in too much time into this because I bought it on the description of, everything working great 100%.  Also, I noticed that someone had been in this before likely looking at the same problem, as VR3 had been resoldered.

[scatterandfocus]

I'm back to looking at this power supply.  I was waiting on a soldering station so that I don't butcher the joints in this thing with my trashed pencil iron with a tip that looks like a dog chewed on it.  Where I left off in the service manual is table 5-5, pdf pg. 58.  When shorting test points 65 and 66 I get no voltage, which table 5-5 indicates an open in Q8-Q11 and/or an open in R68, R69, R73, R74, or VR3 shorted.

It looks like the frame has to be nearly completely disassembled to pull Q8-Q11 for testing (going to be a pain).

Since this is the only supply that I have at the moment and the master side is working, I'm wondering here if I could pull components from the slave side for testing and still use the master side for testing VR3.  All of these components are in the series regulator section on the slave board of the schematic, pdf pg. 4.

[scatterandfocus]

Maybe I should be posting this in the beginner section.

Got the legs lifted on the zener and resistors.

I'm not sure if resistance testing a zener diode is valid.  For VR3, I'm getting 0.67 ohms with the negative lead to cathode and infinite with negative to anode.  That at least indicates that the diode isn't shorted.

For R68, R69, R73, R74, I'm getting around 0.5 ohm, but these measurements seems sketchy, because I get 0 ohms in the lowest position/continuity, and 0.8 ohm (including test leads) in the 200 ohm position.  This at least indicates that none of the resistors are open.

So it seems likely that I should have an open transistor, according to the service manual.  I got the frame partly disassembled to get at the transistors, but I will have to finish that tomorrow.

[scatterandfocus]

I got the frame apart and slave side Q8B-Q11B transistors out as well as master side Q11A out (a known good transistor for comparison) and did some simple resistance testing.  The highest setting on my meter is 20M ohms range.  I tried all manners of resistance testing, but this is what seems notable to me:

For reference, the known good Q11A shows:
+ emmiter, - collector, rapidly goes out of range
- emitter, + collector, slowly goes up to around 20M ohm

Q9B and Q10B:
+ emmiter, - collector, rapidly goes out of range
- emitter, + collector, rapidly goes out of range

Q8B and Q11B:
+ emmiter, - collector, rapidly goes out of range
- emitter, + collector, slowly goes up to around 14M ohm

So it seems likely that Q9B and Q10B are open, which is also in line with what the service manual says.

One thing that I am wondering about here is the HP 'selected' RCA 2N3055's used in these old power supplies.  If I just grab some ON Semiconductor 2N3055's, will there likely be any issues?  I'm also wondering what might have caused Q9B and Q10B to go open.  Are transistors just prone to fail over time for no particular reason?

If anyone is reading this muckaruck, any thoughts are welcome.

In post #10 over here, there were some pages from the 1977 RCA data book on the 2N3055 data:  https://www.vintage-radio.net/forum/showthread.php?t=138407  So as best as I can tell, I should be looking at the ON 2N3055AG for a modern manufactured replacement.  So I guess continuing with trying to get this thing working will be on hold until I get the parts.  And I might as well see what I can figure out on a 465B that has issues before ordering my parts.  Maybe I can order what I need at the same time.

[scatterandfocus]

I'm thinking that I should put this thing back together and start back from square 1, looking back over the manual on the series regulator and comparing voltages in the series regulator sections of the master and slave sides. 

[Ordinaryman1971]

I think you could use 3055 for the NPN transistors in TO-3 packages. Those are pass transistors and it would be good replacement.
Talking about fixing it....
Yes, put it together. You do need a multimeter and soldering iron and copy of manual... readily available on web.
Try to read about the theory of operation, and understand how it works. I know it's not all clear at the first read, don't worry.
There is a block diagram of how the things are tied together. Just look and understand what was is the relationship between all the modules....
Describe starting condition you are in.
Do you have any output?
Can you adjust it, whatever that is?
Is there anything getting hot?
Check all the power rails... follow the troubleshooting in the manual, you can compare with the other channel if it's working right, they are identical.
Then... if all the power rails and reference voltages are right get deeper in troubleshooting.

[Ordinaryman1971]

The normal strapping for the supplies has to be exactly how it is shown in the manual. Make sure you have it the way it's shown in manual, otherwise... it won't work.
Please double check, you will troubleshot and put hours in checking everything just to go back and find that the strapping was off.
Tight all the screws on terminals, you can buzz them through with your continuity check to make sure they are "there".

[Ordinaryman1971]

And... did you check fuses? There are two fuses on the bottom of the supply.. Open the bottom cover and they will be right there on the edges of the board. They are 3A 250V. Make sure they are ok.
Sorry... just read through you comments and found you've changed it already.

[scatterandfocus]

Thanks Ordinaryman71.  When I got this thing, there was no output on the slave channel and nothing showing on the panel meter.  The strapping looked to be correct according to the service manual.  Opening it up, there was a blown fuse on the slave side.   I replaced the fuse with a lower value fuse (all I had on hand), and it did not blow.  It was also obvious that someone had pulled a leg of VR3 to test it (and soldered it back).    I followed the troubleshooting tables in the service manual to table 5-5, which indicated an open in Q8-Q11 and/or an open in R68, R69, R73, R74, or a short in VR3.  All resistors and the zener checked ok.  Diode testing the transistor junctions also looked ok.  Resistance testing junctions of the transistors showed a couple of them to have much higher resistance than others (including a known good resistor from the master side), but I don't know if that really indicates a fault in those transistors.  They aren't fully open, but at room temperature they are showing to be in the 100M ohm range, where others are in the 15M-20M ohm range.  At that point, not knowing if the transistors are bad or not, I have decided to put it back together and check some voltages.  Today I have been reading over the theory of operation to get a better idea of how everything works.  It has been as you described, not understanding everything that I read, but parts of it are coming together, at least in a sense of how the various blocks interact.  I'll continue reading over the service manual, get the thing back together, and see what I can figure out.

Also, it has been helpful to print out some sections from the service manual to look at while reading from the pdf, such as the schematic at the top of the manual.  Trying to read schematics from a pdf is a pain.  I may just see if I can get away with printing the whole manual at work tonight.