PDA

View Full Version : HQ-129X Repair Help



N3HEE
01-31-2012, 02:02 PM
I got my dead HQ-129X running good but I have a strange problem that I cant seem to solve. The receiver will work fine for random periods of time then will start to fade in volume. Sensitivity is still OK but overall volume drops quite low. Now for the strange part. If I simply touch the grid pin of the 1st IF amp with the tip of a screw driver the radio comes back to life. Nice and strong. After that it may play good for many hours or may only play good for 15 minutes. Touch the grid pin again and the radio will come back to life. I have replaced all of the IF and RF side tubes as well as the audio output tube with known good tubes. I have recapped the entire radio, all voltages look good. Nothing is getting abnormally hot. Tube sockets have been cleaned. The unit has been aligned. In my mind, this appears to be some sort of capacitance issue. Could I have a bad IF can? Has anyone seen this behavior before? Thanks for any help. I'm out of answers. -Joe

KB4QAA
01-31-2012, 04:02 PM
So, you have confirmed that you really do have The Golden Screwdriver!

KA4DPO
01-31-2012, 05:37 PM
I got my dead HQ-129X running good but I have a strange problem that I cant seem to solve. The receiver will work fine for random periods of time then will start to fade in volume. Sensitivity is still OK but overall volume drops quite low. Now for the strange part. If I simply touch the grid pin of the 1st IF amp with the tip of a screw driver the radio comes back to life. Nice and strong. After that it may play good for many hours or may only play good for 15 minutes. Touch the grid pin again and the radio will come back to life. I have replaced all of the IF and RF side tubes as well as the audio output tube with known good tubes. I have recapped the entire radio, all voltages look good. Nothing is getting abnormally hot. Tube sockets have been cleaned. The unit has been aligned. In my mind, this appears to be some sort of capacitance issue. Could I have a bad IF can? Has anyone seen this behavior before? Thanks for any help. I'm out of answers. -Joe

Replace the grid resistor, it's probably cracked.

N3HEE
01-31-2012, 05:54 PM
I hear that but the control grid is connected directly to the output of the previous (Mixer) stage's IF can. No resistor. Also, I am not applying any pressure when I touch the grid pin. The screw driver is barely contacting the pin. So I am ruling out a physical connection issue. I have re-soldered all of the connections around that area.

K9STH
01-31-2012, 06:33 PM
Have you replaced all of the paper capacitors in the receiver? If not, then I definitely suggest replacing all of them before you go any farther. It sounds like a leaky capacitor.

Also, while you are in the receiver, tighten all of the machine screws and nuts that go through the chassis. Also, tighten the contacts on the tube sockets. You can do this by pushing a probe, Xacto knife blade, etc., between the insulating material and the the contact.

Glen, K9STH

N3HEE
01-31-2012, 06:40 PM
Glen, I thought for sure it was a leaky cap as well. I replaced every paper cap in that radio and still no love. I will do the other things you suggest and report back. Thanks -Joe

K9STH
01-31-2012, 08:04 PM
KJS:

You might have to replace the mica capacitors that are used especially in coupling between stages. Also, a lot of what appear to be mica are actually "micamold" capacitors which are actually paper capacitors, not mica!

Glen, K9STH

KA4DPO
01-31-2012, 09:07 PM
That's true and it could be the resonator cap in the IF transformer but it's for sure that that problem doesn't just happen for no reason. I would check all of the other resistors in the RF amp as well just to make sure that touching the grid pin doesn't apply just enough pressure to fix it. One easy way to do it is to get some freeze spray and then just wait for the problem to happen and start selectively spraying components.

N3HEE
02-01-2012, 12:08 AM
I failed to mention that I can also resolve the problem by switching the send receive switch from receive to send and back again. This removes B+ from the screens of the IF/RF section tubes. I will probe around some more and check out other caps\resistors in the area. Crazy problem. Could this be related to the silver mica "disease" that the caps get inside of the IF cans? I read that some Hammarlund radios are plagued with that problem. However the symptoms are not the same. They say the radio starts making loud noises similar to a thunder storm.

WB5WSV
02-01-2012, 03:47 AM
The only thing I could suggest would be to take another receiver, one that can tune 455 KHZ, loosely couple it's antenna input to the beginning of the HQ-129X IF, and then see if the problem when it occurs happens on both the 129X and the other receiver. That would help you isolate the problem to the IF or RF stages.

A BC-453, BC-348, ARC R-11A, or Ten Tech 1254 are examples of sets that can tune 455 khz.

Good Luck - and be sure to let us know what you find!

Robert
WB5WSV

KA4DPO
02-01-2012, 02:54 PM
The resonator caps in the IF transformers have been known to fail and the problem you describe woul definetly point to that as a potential problem. Again, if removing B+ momentarily restores operation you have a bad cap or busted resistor. A broken or cracked resistor can heat up and expand just enough to open. If it is a cathode resistor then gain disapears. A capacitor can also break down when it reaches some critical temperature. The easiest way to find this problem is using cool spray and a non-conductive stick to gently rapp on resistors and try to get or relieve the problem. It sounds like a single component but could even be a cracked solder joint or a loose chassis ground so don't overlook the obvious stuff.

N3HEE
02-06-2012, 05:46 PM
PROBLEM SOLVED ! It turned out to be a bad connection in the T3 IF can. One of the coil wires had come loose.

ad: cq2k-1