Lafayette HA-230: I couldn't help myself!

specops56 · Posted: Nov Wed 04, 2009 3:10 am

I just had to crack open that free Lafayette HA-230! The gentleman that gave it to me said that he picked up some broadcast stations but when I powered it up I got nothing but low power supply hum. Not enough to indicate bad filters though. You have to hold the speaker up to your ear to hear it. Besides, I clipped in subs for all the filters and no difference. This set requires an external speaker so I clipped one on the terminals on the back of the chassis. I learned a lesson today. I learned that a filament transformer looks a lot like an audio transformer. To check to see if the speaker terminals were bad I touched the clip leads to the terminals on what I thought was the audio transformer. Blew the fuse and a big hole in the speaker cone! Good thing it was a cheap and expendable speaker. But it did allow me to learn that a previous owner had replaced what was supposed to be a 2 amp fuse with a 1 amp fuse. The closest I had was a 1.5 amp so I put that in for now just for testing purposes. I subbed the rectifier tube, the 1st audio tube and the output tube with no change. I subbed the .005 cap that's across the audio transformer (the real one this time) and no change. So I believe I've narrowed it down to the RF section. I'm going to try to make some voltage readings on the tubes and do some signal tracing. My problem is that all I have is a schematic and no parts layout pictures so it's going to be a challenge for me. If anyone has worked on this model has any advice to give me I'd certainly be grateful!

Terry
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Peter Bertini · Posted: Nov Wed 04, 2009 1:49 pm

Terry

On the back apron, is there a five-pin accessory socket?

Is the black accessory plug installed? I believe it is needed to operate the receiver. The plug has a jumper that controls the external muting for the receiver.

Pete

specops56 · Posted: Nov Wed 04, 2009 4:30 pm

Peter:
The answer to both your questions is yes.

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

Dave Doughty · Posted: Nov Wed 04, 2009 4:42 pm

Is your set filled with gray Japanese paper caps? These are notorious for shorting and taking out other components like screen resistors.

Dave

specops56 · Posted: Nov Wed 04, 2009 6:00 pm

Well, I figured out the problem and it's not good news. The power transformer stays cold when the set is turned on. The filaments get power from the separate filament transformer which is what threw me off. I've never worked on one that had this arrangement before. Now that I figured it out it makes sense that I'm not getting any signal since there's no operating voltage for the tubes. The transformer has had some heat before but it didn't look all that bad so I never connected it in my head. I take solace in the fact that it looked the same and had the same symptoms before I blew the fuse so it wasn't me that fried it! Here are some pics:

I've never had a bad power transformer before so I have no idea how to test it to see if it can be saved. HELP!

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

Dave Doughty · Posted: Nov Wed 04, 2009 7:22 pm

The complete manual for this set is available here:

http://bama.edebris.com/manuals/lafayett/ha230/

I have one of these sets but I haven't restored it yet. The schematic shows the separate filament transformer powers the mixer and oscillator tubes at all times, even when the power switch is off. This is probably an attempt to minimize drifting from a cold start. The other tube filaments get powered from the main transformer. I wouldn't assume the main transformer is bad until you take some voltage measurements on it's primary and secondary terminals. The problem may be as simple as a bad power switch.

Dave

specops56 · Posted: Nov Wed 04, 2009 8:39 pm

All tubes light when the switch is turned on and they draw about .25 amp of current when they warm up. I also noticed that the 2k power resistor, the reddish one at the transformer does get hot but it measures well within specs. I will take the voltage readings and report the results. BTW, I have subbed all the tubes, one at a time and it made no difference so the tubes seem good.

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

Dave Doughty · Posted: Nov Wed 04, 2009 8:50 pm

That resistor is the B+ filter. It should run warm but not overly hot. Seems like the power transformer is good but there is a short somewhere. Maybe a bad filter cap or one of those bypass caps I mentioned earlier which look like small electrolytics but are actually paper caps with a gray plastic covering. At some point, the Japanese began using disk caps for bypass so it is possible your radio doesn't have these paper caps.

Dave

Arnie-AE · Member Joined: 18 Aug 2009 Posts: 110 Location: Berlin, MA

Hi Terry. It seems like you have an interesting project. I'm wondering what you have for test equipment besides a meter. If you have an audio generator, you can insert an audio signal after the detector to see if the audio amp will work.

I also have a good RF generator and like to inject a 455Khz signal right after the mixer and so on back to the RF section. Even if the IFs have been badly mis-aligned, if you crank up the output level on the generator, you can usually hear something.

If the radio has a crystal calibrator or if you have an external one, that makes a good signal source to put into the antenna jack.

good luck with the investigation.

arnie - W1GCI

specops56 · Posted: Nov Wed 04, 2009 9:09 pm

Dave:
Yeah it does have a bunch of those gray caps. I did sub all the filter caps and it made no difference so they seem to still be good. I also subbed the .005 cap thats across the audio tranny and again, no difference. I think I'll go ahead and sub all the rest of those gray caps and see what develops.

Arnie:
I got test gear coming out of my ears! Much of it I have no clue how to use but I got it. I do know how to use my siggen though.

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

specops56 · Posted: Nov Wed 04, 2009 10:48 pm

I decided to try subbing those gray caps and see what I got. When I subbed C23, the .01mf cap connected to pin 1 of the 6AV6 1st audio, I suddenly got loud filter cap hum out of the speaker. So I think a recap is in order before going any further.

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

Dave Doughty · Posted: Nov Thu 05, 2009 1:07 am

Have you taken voltage measurements yet?

DAve

specops56 · Posted: Nov Thu 05, 2009 3:35 am

Okay, here's what I've measured so far (I'm working on it off and on between Honeydos!):

Input voltage is 117 vac

I measured dc volts across all the filter caps: The can has C26 and C27 which measured 123vdc and 219vdc respectively. C24 measured 7.8vdc.

The 5Y3 rectifier measured as follows referenced to chassis:
Pin 2= 218vdc
Pin 4= -17.5vdc
Pin 6= -17.5vdc
Pin 8= 217.4vdc

That's all I've got so far. I don't know what the voltages are supposed to be because it's not marked on the schematic and that's all I have. Please help me to interpret these readings. Confused

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

Mbird97x · Member Joined: 01 Jan 1970 Posts: 1854 Location: NE Fla.

Dave Doughty · Posted: Nov Thu 05, 2009 12:05 pm

Using ohms law, I calculated that the current being drawn from the power transformer is about 50 ma and the power being dissipated in the filter resistor is about 4.5 watts. This seems OK because the power transformer says it can do 70 ma and the resistor is stated in the schematic as rated at 10 watts. The voltages you measured across each filter cap seem about right.

You should be seeing about 200 volts AC on pins 4 and 6 of the 5Y3, not DC.

When you said you "substituted" the caps, do you mean you replaced the caps?

Next, I would recommend taking voltage measurements on the plates and screens of each of the tubes.

You can then test the audio stages by connecting the audio ouput from your signal generator to the "high side" of the volume control and the chassis.

Dave

specops56 · Posted: Nov Fri 06, 2009 1:42 am

Jack Shirley · Member Joined: 14 Mar 2008 Posts: 2459 Location: SE USA

specops56 · Posted: Nov Sat 07, 2009 12:43 am

Okay, I just spent the last few hours making tests and my results are below. For the voltage readings I set the controls just as the OM instructions said and set the variac to 117vac. First, here is a copy of the manual page with what the readings are supposed to be:

And now my readings ( I forgot to to measure V4 the BFO/Q multi. tube so if it's important I can go back to it.):

V1/6BA6/RF amp:
P1= -205 mvdc
P2= 0
P3= 6 vac
p4= 0
P5= +137.6 vdc
P6= +135 vdc
P7= +4.5 vdc

V2/6BE6/Mixer:
P1= -7.5 vdc
P2= +4 vdc
P3= 5.9 vac
P4= 0
P5= +127 vdc
P6= +126.8 vdc
P7= +364 mvdc

V3/6BE6/Osc:
P1= -7.7 vdc
P2= +6.8 mvdc
P3= 5.9 vac
P4= 0
P5= +127.1 vdc
P6= +127.1 vdc
P7= +127 vdc

V5/6BA6/1st IF:
P1= -224 mvdc
P2= 0
P3= 6 vac
P4= 0
P5= +137.6 vdc
P6= +137.5 vdc
P7= +16.8 vdc

V6/6BA6/2nd IF:
P1= 0
P2= 0
P3= 6 vac
P4= 0
P5= +138.3 vdc
P6= +138 vdc
P7= +17.2 vdc

V7/6AV6/Det-1st AF:
P1= -666 mvdc vdc
P2= 0
P3= 6 vac
P4= 0
P5= -478 mvdc
P6= -716 mvdc
P7= +63.5 vdc

V8/6AQ5/AF output:
P1= +4.6 vdc
P2= +10.2 vdc
P3= 6 vac
P4= 0
P5= +211.5 vdc
P6= +136.7 vdc
P7= +4.9 vdc

Most of these voltages are a bit high it seems to me. I'm thinking this would be an indication of some bad caps?
I next hooked up, through a .01 cap. a probe to the high side of my siggen and the low side clipped to chassis. I proceeded to start injecting a 500khz audio signal into the set. Starting at the volume control I got a loud, clear signal from the speaker which varied with the control as it should. That indicates to me that the audio section is working fine. I then switched to modulated RF at 800khz and turned the dial to 800khz. I first touched the probed to the tuning capacitor gangs. The rear and middle gangs gave me a loud and clear tone, the front section gave nothing.
I then touched VI/P5, V2/P2 and V3/P7 (I might have V2 & V3 reversed) and got loud and clear tones each time. This would seem to indicate to me that the RF section must be working fine too. So right now I'm stumped! I never have been able to interpret voltage readings worth a horse apple. At this point I'm thinking I should go ahead with a recap and see if anything improves as I replace them one by one.

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!

Dave Doughty · Posted: Nov Sat 07, 2009 2:19 am

The voltage readings look fine except the grid reading on the 6AQ5 (pins 1 and 7). But since you have audio, it's working. At some point you will probably want to change the coupling cap and perhaps the tube.

If the front section of the tuning gang is the oscillator section, you should hear nothing with the signal generator connected.

Do you have the IF gain control turned fully clockwise and a good antenna connected?

Dave

specops56 · Posted: Nov Sat 07, 2009 2:29 am

Dave:
One of the first things I did was to sub another 6AQ5 and it made no difference so I believe the tube is good. The manual said to turn IF gain to minimum and jumper the antenna connection before taking the voltage readings so I did. But I removed the jumper and turned the IF back to maximum for all other testing. I did have a good antenna attached for all my earlier testing. As for the coupling cap I assume you mean C23? I do plan to change that. I intend to start recapping this thing tomorrow.

Terry
_________________
Always bring more ammo than you think you will need because you will always need more ammo than you brought!