ad: elecraft

HQ-180A IF Mystery

Discussion in '"Boat Anchor" & Classic Equipment' started by KW4H, Jan 19, 2022.

ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: Radclub22-2
ad: Left-3
ad: l-BCInc
ad: Left-2
ad: abrind-2
  1. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    After using my newly-restored HQ-180A for a while, it was clear that -- although the radio works -- it's rather noisy, the audio is a little bizarre (almost muffled at times, and a bit distorted), and sensitivity nowhere near what it should be. To make a long story short, I was able to determine that someone has fiddled with the IF alignment in the past and left their mess behind. Time to do an IF alignment.

    The behavior I'm seeing is mystifying -- please see the attached schematic. This is the 60 KHz IF section. To align, all you do is put a VTVM on the product detector output, inject an unmodulated 60 KHz signal into the grid of the 2nd converter, and peak up T6/7/8/9/10/11 (maximum NEGATIVE voltage). However, when I inject a 60 KHz signal into the 2nd converter the radio is deaf as a doornail. I'm using a SG-85 and have jammed the signal level WAY up higher than necessary, and you can barely move the needle on the VTVM. As called for in the instructions, this is with the radio in AM mode, the sideband control in USB, and the bandwidth in .5. However, if you broaden the bandwidth and set the sideband control in "both", the 60 KHz signal becomes discernible. At that point, and as an experiment, I looked for a peak with T6 and T7. I could find a peak with T6, but T7 has no peak, but it tries to find a peak when you run the slug all the way to the top or bottom of its run. Very odd and not what it should be doing.

    As a next step, I injected the 60 KHz signal into the grid of V7. This only left T10 and T11 to fiddle with. Blammo! The signal came through -- much better! However, T10 and T11 exhibit the exact same relationship as T6 and T7. I can find a 60 KHz peak on T10, but T11 behaves identically as T7 -- no real peak, but an increase in signal at the top and bottom of the adjustment.

    Anytime I see something like this -- where two different stages are behaving in the same unusual manner, I always look for something in common. In the case of the HQ-180A, what's in common are a bank of wafer switches, which Hammarlund annoyingly parked right over top of the IF section.

    Am I going down the right path with this, or have I wandered off course in diagnosing this? Even considering the wafer switches, when I look at T11 and T7, I can't really see a reason why they would both fail to find a peak. But I have more digging to do.

    Appreciate any thoughts/advice.

    Steve, KW4H

  2. K1APJ

    K1APJ Premium Subscriber QRZ Page

    Are you absolutely, positively certain that your signal generator is on EXACTLY 60 kHz?
    KA0HCP and KW4H like this.
  3. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Yup. That was the first thing I ran to. The signal generator was checked against a known good frequency counter. Also -- I have another signal generator that measures right on the money and switched to that one just for grins. No difference.

    Steve, KW4H
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    K1APJ beat me by seconds. How confident are you of the 60kc accuracy of your signal generator.

    -The test path is quite long and includes (too many) irrelevant components which could also have failures.

    --I would connect test leads directly to the input and output points of each IF section set.

    Each IF section is a 'tuned circuit". The common component among them is the IF capacitor. Other radios have had failures of the IF capacitors. This is generally driven by the quality and type of the capacitor design.

    If the IF's can't be properly aligned, then it may be necessary to open a sample can and inspect the cap for corrosion, warping or failure of plastic/mica dielectrics. Generally the caps can be replace with an modern cap placed externally after disabling or removing the internal cap.
    N8YX, KD2ACO, K7TRF and 1 other person like this.
  5. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    I wanted the accuracy of the signal generator to be off, but unfortunately that was dismissed pretty fast. I have multiple signal generators and frequency counters and the 60 KHz was right on. I kept cross-checking things looking for bad equipment or missteps on my part but couldn't find anything. To your point - the Hammarlund alignment procedure does use a rather long path, but of course the instructions were written in an era when the radio wasn't 50 years old. I'm going to have to take this in bite-size chunks and will do so. My greatest fear is having to remove and service the wafer switch assembly beneath the IF section. And if the IF cans themselves need to be inspected, removal of the switch assembly is unavoidable. That's a mess. Yikes -- just when I thought this restoration was about over with....

    Steve, KW4H
    KA0HCP likes this.
  6. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Good advice! And I have some new information. I was able to pull a sample can without actually pulling one -- I have a donor HQ-180A of the exact same vintage and pulled T-6 as an example. Beats the mess involved with removing it from the operating radio. Anyway -- I think we can move a problem within the cans themselves to the bottom of the list. The capacitor is a dipped silver mica and those very rarely go bad -- the awful ones, which almost guarantee SMD, are the mica open leaf construction. Those were apparently used in early HQ-170/180 construction, but not in the later units.

    I'm gravitating back to studying the wafer switches -- the selectors for bandwidth and sideband that are parked over top of the IF section. There's also a bunch of resistors on that switch assembly that could have drifted. I'm desperately trying to avoid pulling the switch.

    The battle we sometimes fight with these wonderful old radios is that the manufacturers never built them to last 50 or 60 years. Hammarlund's design team had no problem parking that switch assembly directly over the IF section, blocking almost all access, because they weren't designing the radio for serviceability years down the road.

    Steve, KW4H
    N2EY and KA0HCP like this.
  7. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Found this great video on removing and reinstalling the wafer switch assembly. This is for a HQ-170A, but the method would be identical for the HQ-180A. This also allows full servicing and alignment with the switch assembly outside of the radio -- which permits more complete troubleshooting and restoration.

    Steve, KW4H
    WA6KNW likes this.
  8. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Today I settled on the fact that the wafer switch assembly is simply going to have to come out. I can't really see and test anything without those switches removed. As much as I like Hammarlund, it's a lousy design from a servicing standpoint. I'm going to follow the procedure in the previously-posted video. While this is going to be a pain in the rear, the end result should be a well-tuned and nicely performing HQ-180A. I fully expect to find that a number of resistors below that assembly, and on the assembly itself, have drifted. This would be in keeping with what I've seen in other areas of this HQ-180A. In fact, I found at least two resistors that drifted DOWN in value.

    Steve, KW4H
  9. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Posting this so that others with HQ-180A's that may want or need to pull the wafer switch assembly blocking access to the IF chain might find the information in the future. Per the attached photo -- looking from the rear of the underside of the chassis forward, you can see that the switch assembly is comprised of 12 switch banks. Using a fine-point sharpie, mark them A through L, starting at the top left (A-B-C-D), and then going back up to the right-top, from the top-down (E-F-G-H-I-J-K-L).

    Also attached to this posting is the complete inventory of the connections you will need to cut in order to remove the switch bank. The inventory gives you the switch bank letter (A through L), the wire color as built by Hammarlund, and a wire number. Each wire also has a "switch position" and "chassis destination". Your orientation when using this is just as it shows in the photo: the chassis upside-down, with the rear of the chassis toward you. The front panel is ahead. The "switch position" notations are indicated by hours on the clock, and whether the wire is soldered to a lug on the switch bank that's FACING you or on the BACK of the switch as you see it. Finally, the "Chassis Destination" is given, and for the tubes it's the pin numbers. For the transformers it's the transformer pins as you see them from the position in the photo -- again, that's with the chassis upside-down, with the rear of the chassis towards you and the front panel ahead.

    You will note that two of the switch banks (C and L) have no wires going to the chassis to cut.

    Those 12 wires are the ones you need to cut. Once you cut them, remove the four screws holding the switch assembly frame to the chassis, and then pull UP and BACK to remove the switch assembly. You have to pull back because of the switch rods sticking out of the front panel. Do it gently -- it will play a little tug of war with you because of a couple of components on the chassis rubbing against the bottom of that L-bracket.

    I also believe I finally figured out how Hammarlund built that switch assembly. It was most likely originally manufactured from the front to the back of the radio, installing the wafer switches in layers. It must have been quite an assembly line!

    73 - Steve, KW4H
    Switch.jpg Switch Inventory.png
    Last edited: Jan 21, 2022
    N8YX, KD2ACO and KP4SX like this.
  10. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Today I pulled the switch using the procedure posted above. Everything went as noted, but I did find one small error (but an important one) on the switch connection inventory. For switch bank B, Green wire color, the chassis destination is T-9, bottom right, not bottom left. See corrected inventory below.

    Steve, KW4H
    Switch Inventory.png
  11. W2ILA

    W2ILA Ham Member QRZ Page

    Looking forward to next steps.
  12. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Update: yesterday I tested every resistor and inspected every wire, joint, and tube base underneath that switch. Some repairs were made -- a sloppily soldered connection and a ceramic disc capacitor that was burned from that sloppy soldering. Some resistors had drifted, but not out of spec. Those are best left alone. The next step is to inspect and clean the wafer switch array. It will be much easier and thorough with the switch out of the radio.

    Steve, KW4H
    N2EY likes this.
  13. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Work is progressing on the switch array -- but for the record there's an easier way to attach the new wiring between the switch wafers and the chassis. The gentleman in the online video attaches the new wiring to the chassis first, and then to the switch. I'd recommend the opposite -- as you're testing and cleaning the switch array, attach a 12" length of 22-gauge stranded wire to each of the tie points on the switch array. Label each wire with the wire number from the spreadsheet. Then when you mount the switch temporarily on the side of the chassis, you solder the wires to the chassis (trimmed to length as you please). The result is the same, but it's easier and possibly a little less error-prone.

    Steve, KW4H
  14. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    The switch has been cleaned and prepped. And a correction: the video does, in fact, show the switch being wired before attaching the wires to the chassis. Up tomorrow -- attaching the switch to the side of the chassis and then wiring it back in. The new wires are 22 gauge stranded Remington PTFE, rated for up to 600v.

    If you have a HQ-170A/180A receiver and suspect problems in the IF chain, you may find it necessary to pull this switch and reconnect it in a way that allows the radio to function while you do further diagnosis and complete the alignment. The switch array covers up a whole string of tubes and components and makes it impossible to even get a test lead into many locations.

    Steve, KW4H

    N8YX and KP4SX like this.
  15. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    OK, folks -- the switch is mounted, wires connected, and the HQ-180A is operational again. These two photos show you what the external mounting looks like -- the switch is rotated 90 degrees from its mounting in the chassis. The knob on the right is the side band switch, the knob on the left is bandwidth.

    As you can see by the photo on the right, this arrangement allows full access to the IF section while the radio is operating, which allows for troubleshooting and repairs that would otherwise be impossible with the switch installed. The next step is to restart the alignment process. If I'm lucky (which is rare) the problem was the switch itself (it went through some intense cleaning). If any transformers are bad, I have a donor HQ-180A.

    Steve, KW4H

    hq180a_kw4h_switchoutsidefront.jpg . hq180a_kw4h_switchoutsidebottom.jpg
    KD2ACO likes this.

Share This Page