HQ-180A - S-Meter Issue RESOLVED

[KW4H]

I wanted to post the resolution to this in the main thread, but something happened there and no new postings are visible.  Could be something on my end, dunno -- but here we are.

OK, the fix for this isn't what I expected but it works fine.  After thinking on this some more, it became pretty clear that I was chasing a ghost with V-8.  The reason is that AVC DOES work.  Off/Fast/Med/Slow works and sounds as expected -- therefore AVC is obviously getting through.  Therefore, this issue has to be entirely focused on the meter circuit.  I found another HQ-180A schematic and there it was -- R22 had a rating of 820 ohms.  However, the rating of R20, the zero adjust pot, was 300 ohms in that diagram.  In the HQ-180A I have, R20 is 1500 ohms and R22 is 470 ohms.  Clearly, these resistances can be toyed with - Hammarlund did it.  I removed R22 and, using clip leads, experimented with some resistor values until I found pay dirt -- the circuit balanced out nearly perfectly by replacing R22 with -- guess what? -- a 820 ohm resistor.  I was also now able to adjust a 50uv signal to S9.

After all this fuss, I think the underlying cause was age.  Although I replaced all of the resistors in the bridge circuit for the S-meter, there are some things that can't be easily changed, such as the wiring itself.  The wiring from the meter circuits to the meter itself, and the AVC switch, is buried in harnesses.  I did ohm out the wiring to the AVC switch and it seemed fine, so this might be the meter connections.

I don't like modifying things from the original, but this was relatively minor and, from an electrical perspective, is mostly cosmetic.  However, as an afterthought, it might be a worthwhile modification to replace R22 with a 1.5k potentiometer and call it "Bridge Balance".  This would allow for a finer adjustment of the S-meter bridge.  Basically, you adjust the resistance so that the meter remains at the zero point when you flip the AVC switch to different positions.

The only thing left to do is a little more cleaning and to check the alignment.  The upper band is noticeably quiet.  Using K7PP's protocol, I was able to determine early-on that the 60 KHz IF is properly aligned and shouldn't need to be fooled with.  Hopefully, all I'll need to do is touch up the RF alignments and call it done.  

I sincerely appreciate the time and effort that others have put in to helping me deal with the S-Meter issue.  This was a great learning experience.

73, Steve - KW4H

[Pete, WA2CWA]

OK, the fix for this isn't what I expected but it works fine.  After thinking on this some more, it became pretty clear that I was chasing a ghost with V-8.  The reason is that AVC DOES work.  Off/Fast/Med/Slow works and sounds as expected -- therefore AVC is obviously getting through.  Therefore, this issue has to be entirely focused on the meter circuit.  I found another HQ-180A schematic and there it was -- R22 had a rating of 820 ohms.  However, the rating of R20, the zero adjust pot, was 300 ohms in that diagram.  In the HQ-180A I have, R20 is 1500 ohms and R22 is 470 ohms.  Clearly, these resistances can be toyed with - Hammarlund did it.  I removed R22 and, using clip leads, experimented with some resistor values until I found pay dirt -- the circuit balanced out nearly perfectly by replacing R22 with -- guess what? -- a 820 ohm resistor.  I was also now able to adjust a 50uv signal to S9.

After all this fuss, I think the underlying cause was age.  Although I replaced all of the resistors in the bridge circuit for the S-meter, there are some things that can't be easily changed, such as the wiring itself.  The wiring from the meter circuits to the meter itself, and the AVC switch, is buried in harnesses.  I did ohm out the wiring to the AVC switch and it seemed fine, so this might be the meter connections.

I don't like modifying things from the original, but this was relatively minor and, from an electrical perspective, is mostly cosmetic.  However, as an afterthought, it might be a worthwhile modification to replace R22 with a 1.5k potentiometer and call it "Bridge Balance".  This would allow for a finer adjustment of the S-meter bridge.  Basically, you adjust the resistance so that the meter remains at the zero point when you flip the AVC switch to different positions.

73, Steve - KW4H

In Addendum No. 9001-15-00001. for the HQ-180 series (180, 180A, 180AX, 180XE) R20 was changed from 300 ohms to 1.5K ohms. R22 was changed from 820 ohms to 470 ohms. R99 (shown on the diagram you provided) was changed from 1K ohms to 2.2K ohms.

The Addendum is two pages. I believe the manual and attached 4 schematics were issued at least 4 times during the life of the model.

Hammarlund also issued an Addendum, K41387-2, specifically against the HQ-180A. It basically targets late model HQ-180A's, with separate filament transformer, 3 position BFO switch, solid-state power supply, new accessory socket, new system socket, new voltage and resistance charts.

[KW4H]

In Addendum No. 9001-15-00001. for the HQ-180 series (180, 180A, 180AX, 180XE) R20 was changed from 300 ohms to 1.5K ohms. R22 was changed from 820 ohms to 470 ohms. R99 (shown on the diagram you provided) was changed from 1K ohms to 2.2K ohms.

The Addendum is two pages. I believe the manual and attached 4 schematics were issued at least 4 times during the life of the model.

Hammarlund also issued an Addendum, K41387-2, specifically against the HQ-180A. It basically targets late model HQ-180A's, with separate filament transformer, 3 position BFO switch, solid-state power supply, new accessory socket, new system socket, new voltage and resistance charts.

Interestingly, "R99" in my two HQ-180A's is 470k and it appears to be factory.  But it shows as R91 on the schematic, not R99. One parts list shows R99 as 2.2k, another one doesn't even list an R99, but does list R91 at 470k.  In the process of peeling this onion, I've run across multiple discrepancies -- including the diagrams, statements in the manual(s), and the resistance and voltage charts.  I love the HQ-180A for many sentimental and technical reasons, but OMG the documentation is a circus.  Hammarlund made great radios, but I wonder if they were dysfunctional with some of the details and documentation. 

Steve, KW4H

[Pete, WA2CWA]

When the last President of Hammarlund passed, a good portion of his amateur radio stuff was sold at the Gaithersburg, MD hamfest in the mid 90's. I picked up a number of original Hammarlund manuals and other information that were being sold. I do remember several HQ-170A and HQ-180(A) manuals having their schematics marked up with circuit changes (mostly minor and/or value changes) and some with notations, "send to manufacturing to implement". Evidently he liked to remove his President hat and put on his engineering hat on the weekends. How many of these changes got implemented and how many actually got into the parts lists and schematics and into manufacture, we'll probably never know.

If you look at some of Hammarlund's earlier schematics in the "HQ" line, they seem to flow left to right reasonably well. However, with the HQ-170 and 180 series of receivers, the schematics in sections seemed to be really jammed up and didn't really flow that easy to follow. 

[KB9ZOX]

Great info!  I'll now have to check my 180A (and my 170A), they both have similar S meter issues.