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Author Topic: Heathkit Hw-100 repair  (Read 7032 times)
WB2JOB
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Posts: 14




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« on: July 07, 2013, 02:06:40 PM »

Just picked up a Heathkit HW-100 radio, when I got the radio the first thing I did was replace both 20 uf electrolytic capacitors, the 2 10 uf cap checked good so I didn't replace them.
Here is what I get and hope someone can help me with what I'm getting.
I'm able to set the BIAS to read 50 Ma in the TUNE position and the METER switch in the PLATE position.
In the REL PWR position I' able to adjust both the MIC/CW LEVEL, PRESELECTOR and FINAL TUNE for max out put, I'm getting 100 Watt on my MFJ antenna tuner.
When I return the MIC control and put the switch in the PLATE position and speak into the MIC while I advance the MIC control I get nothing.
I have changed 6EA8 speech amp, 12AU7 carrier osc, 6AU6 ISO Amp, 6AU6 first IF amp, 6EA8  first trans mixer, both finals.
I know it not the Mic because when I put the radio in CW mode and use key and still get no output.
Hope someone may be able to set in the right direction to get this radio working.
Thanks
Bob
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AB1MN
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Posts: 41




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« Reply #1 on: July 08, 2013, 05:56:33 AM »

DO you hear the relays click when trying to transmit? Are you using vox or ptt? Ptt should pick the relays directly while both vox and cw rely on the vox circuit to pick the relays.
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WB2JOB
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Posts: 14




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« Reply #2 on: July 08, 2013, 07:51:47 AM »

Hi
Yes when I key the mic I hear the relay kick in, I'm in the PPT mode and also talk into the mic as I increase the mic gain control but still no output.
Bob
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KD0REQ
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Posts: 849




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« Reply #3 on: July 08, 2013, 08:36:04 AM »

CW is A4 on the HW-10x radios, so it's tone-modulated instead of the mic.  same issue.

there are TWO relays in the system, and it may be advantageous to power down, spark off the B+ and B++, pop the covers, and burnish the contacts with a piece of high-cotton printing paper.  one inside the RF cage, one out.

otherwise, the tried and true clean-da-switches and checking for high resistors way, way out of value are interesting paths to follow.
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WB2JOB
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Posts: 14




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« Reply #4 on: July 10, 2013, 09:13:17 AM »

Hi
Checked both relays, the one in the high power side was a little dirty and I cleaned that one and also the small one on the top of the unit ( that one was pretty clean), check the 2 resistors going to the high power relay a 330 ohm resistor was ok ( it read 328 ohms) but the 10k Was reading almost 29K, so I will be changing that one just as soon as I can get to Radio Shack. Both relays click in as I key the Mic. but still no output, have to change that resistor and see what happens.
Hope that does it.
Bob
« Last Edit: July 10, 2013, 09:40:30 AM by WB2JOB » Logged
AD4U
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Posts: 2152




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« Reply #5 on: July 10, 2013, 10:49:15 AM »

As someone who has repaired numerous Heathkits of questionable origin and build quality, I recommend you do this in this order.

1.  Carefully go through the manual step-by-step and check for the right part in the right place and solder joints as if you were assembling the rig from scratch.  This should not take more than a couple of hours.  Correct any errors.

If everything is OK so far..........

2.  Check each and every resistor for proper value.  The last SB-102 I restored had 37 resistors that were so far out of spec they had to be replaced.

3.  Check voltages and resistances per the charts in the manual.

4.  If the rig still does not work properly replace the suspect tubes with known good ones.  Do not put much trust in a tube checker.

5.  Do a complete alignment per the manual.  Since these rigs are 40+ years old, even one that is working will probably benefit.

6.  If the rig still does not work properly go through the troubleshooting section in the manual.

Dick  AD4U
« Last Edit: July 10, 2013, 10:51:38 AM by AD4U » Logged
WB2JOB
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Posts: 14




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« Reply #6 on: July 13, 2013, 07:35:43 AM »

Thanks Dick for that info.
When I checked that 10K resistor in the unit it read about 29K, after I removed it, it read the correct value, I still replaced it with a new 10K resistor, now when I read the new resistor installed it now reads way below 10K, , but when removed it read 10K.
There is a adjustable core right were the resistor attaches to the relay, I wonder if this should be adjusted, don't know ?.
There is also a diode attached to the same point the resistor go's, don't know the value as it's not marked and having trouble finding it on the schematic.
I'll take the unit out and check all the solder joints and resistor value's as you suggested.
After I tune the unit and put it into REFEL power position and advance the mic the meter first drops below O and then pops up to the right, Still no output in that position.
Also if I adjust the mic to far CW and put it in PLATE position it go's pass the 250 ma and will pop the circuit breaker.
Going to keep going cause now it's challenge.
Bob
WB2JOB
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WB2JOB
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Posts: 14




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« Reply #7 on: July 31, 2013, 02:42:08 AM »

Hi Dick
IF nothing else works would you be open to working on my HW-100, at my age (77), it get hard to to work on things any more.
I would be willing to pay you for your time of course .
I would also pay shipping to and from you,any reasonable amount would be ok with me and when I say reasonable a couple $100.00 dollars would be ok.
If this is ok please let me know.
Bob
WB2JOB

P.S. I have a complete manual for the radio, and Power supply and mic.
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KH2G
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Posts: 238




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« Reply #8 on: August 10, 2013, 04:47:26 PM »

Something not right here. You said the 10K resistor read 29k in circuit but 10k out of circuit. Something wrong with that. In circuit it should read 10k or less as there would be other things affecting it but nothing could cause the resistance to increase while in circuit. Smiley
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KE3WD
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Posts: 5694




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« Reply #9 on: August 10, 2013, 05:38:51 PM »

Something not right here. You said the 10K resistor read 29k in circuit but 10k out of circuit. Something wrong with that. In circuit it should read 10k or less as there would be other things affecting it but nothing could cause the resistance to increase while in circuit. Smiley

An old carbon resistor suffering from carbon clumping due to absorbed humidity can. 

Assume the person desoldered said resistor after taking the high in-circuit reading. 

The heat from the soldering iron could have been enough to dry out the carbon and thus it now reads in tolerance. 

Yes, I have experienced this from time to time in old gear of all stripes. 

But such resistor should be replaced anyway, as it would likely start re-absorbing humidity darn near immediately and would be back to the clumped condition shortly. 

And, it would also be quite the generator of thermal noise, too. 


73
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WB2JOB
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Posts: 14




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« Reply #10 on: August 11, 2013, 02:59:31 PM »

I replaced the old resistor with a new one and this also read 29K when it was installed in the radio, when I removed the new resistor is then read 10K.
Both the new and old resistor both read 29k when installed in the radio, but both read 10k when removed.
Bob
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KE3WD
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Posts: 5694




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« Reply #11 on: August 11, 2013, 05:37:02 PM »

I replaced the old resistor with a new one and this also read 29K when it was installed in the radio, when I removed the new resistor is then read 10K.
Both the new and old resistor both read 29k when installed in the radio, but both read 10k when removed.
Bob

The only way I could see that happening is if the ohmmeter probes were encountering some sort of resistance where you connected them.  This is entirely possible, sometimes old flux, corrosion, that sort of thing, can make the reading higher, acting as a series resistance. 

But there is absolutely no way that a proper measurement across a 10K resistor could be higher than 10K. 

Other things in the circuit can only reduce the figure, never add to it.  Kirchoff had plenty to say about that, by the time he got done, we had to call it a Law...


73
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KA5N
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Posts: 4380




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« Reply #12 on: August 12, 2013, 04:55:34 AM »

You can't get an accurate reading on a resistor when it is in-circuit.    The results you are
getting sound peculiar, but who knows what you measuring when it is in circuit. 

I really question offering to pay $200 to get a HW-100 repaired.  There are many more
radios out there that will outperform the HW-100 at a low lower (used) price.  I would sell
the HW-100 and start looking for a dependable good working rig.     
If you happen to have a sentimental attachment for the HW-100, then good luck.

73 Allen KA5N
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KD0REQ
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Posts: 849




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« Reply #13 on: August 13, 2013, 11:26:02 AM »

consider this HW-100 a training radio.  it's training you.  by the time you're through, you will think like a proper debugger of all things old and hollow-state.

if you don't already have the schematic, get it.  check the socket voltages keyed and unkeyed.  where you find wacko voltages that are off more than 10 percent, you have an issue to resolve.  suspect all parts at that stage, including the tin-plated tube socket.  they oxidize.

lots of these rigs have the signal conductor of interboard coax connected to a ground or a bias point instead of the takeoff point of the previous stage.  an oscilloscope is a useful tool for debugging lost AC signals.  just make sure the input circuit can take the voltages expected, both really expected and "oh, look what the golden screwdriver did" expected.  if yours can't, a small disc ceramic rated for voltage-plus, like a 1000 pF, should be your probe, with the scope on the other side.

oh, yes... a kit... look for cold solder joints or rosin joints that insulate the wire from the board.

this is a SSB radio, in which two crystals feed signals to the product detector, and if either marker or sideband crystal is defunct, you will have no signal out of the PD to feed elsewhere.  check for signal, check for PD output.
« Last Edit: August 13, 2013, 11:29:32 AM by KD0REQ » Logged
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