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Author Topic: re: the ft-101e i am working on  (Read 6478 times)
KC7BYP
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« on: July 11, 2013, 01:55:38 AM »

I have the receive working now on the internal power supply. everything is fine except the 600vdc line.  According to the service manual there should be 240vac across the 2 outside wires (if i am reading it right). there is 0 volts across the 2 outside wires of this secondary winding. But I get 247vac with the volt meter between ether outside wire and the center tap. that don't make any sense to me. There should be half the total voltage of the secondary winding when measuring from one outside wire to the center tap.  Just like a power pole transformer. The 2 outside wires of the secondary winding gives you 220vac, the 110vac comes from 1 outside wire and the center tap.  Does this mean I have to replace the power transformer?

Steve
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KC4MOP
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« Reply #1 on: July 11, 2013, 04:15:55 AM »

PLEEEZE be careful with high voltages.
I'm looking at the scheezo online for this transceiver. Have you disconnected the secondary wires from the power supply?...The 240-0-240 leads from the transformer? A defective component in the P.S. could be causing this weirdness. You are correct about what you should be seeing and the strange voltages might be from something gone haywire in the power supply itself. The diodes, capacitors, etc etc. I will keep the diagram in my browser as a reference and wait for your results.
Fred
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KE3WD
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« Reply #2 on: July 11, 2013, 06:10:48 AM »

Your reported voltage readings do not make any sense. 

It may be that you are measuring points other than those from the same secondary. 

That might not be your fault as these rigs have been around a long time and somebody could have changed connection points from what is in the service manual schematic to repair it long ago. 

Transformer might have been replaced with another at some point that has differing connection points. 

Time to disconnect secondary and use your Ohmmeter on the windings to asee what's really going on.  DC won't cloud the issue with the transformer effect from other windings when you are connected to more than one at the same time. 

Have a Variac? 

Disconnect all secondaries temporarily, bring the transformer up by itself on the Variac to about half the rated input voltage of 120VAC, then use your DMM on AC scale to see what the winding connection points really are. 
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KC4MOP
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« Reply #3 on: July 11, 2013, 07:24:58 AM »

Hey BYP what did you do to get the low voltage part of that power supply to work? Did you change any wires around? The schematic does not callout any colors for the various taps (14) on that transformer. There is a 120vac with no center tap. The other secondaries on that transformer each has a center tap. so I hope someone hasn't screwed up the wiring in there.
Take good notes or digital pics of the wiring, If you're going to do as suggested. Does it look like someone has done a lot of soldering??? Still look factory? The schematic does not tell what color the leads are from the transformer
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KC7BYP
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« Reply #4 on: July 11, 2013, 02:09:04 PM »

1st a bit of history on this radio.  I got it from the local cb radio repair shop asis for $100. (the shop owner is a ham operator)  He told me that he made a mistake by loaning the rig out wile fixing the persons hf rig.  By ether bad swr or miss tuning of the plate and load the final tubes and the driver tube were cooked and shorted out. The shop owner just didn't have the time to dig in and fix the rig.  I had to rebuild the rectifier board.  a number of diodes and resistors were blowin and it was blowing the 117ac fuze. The 600vdc line has all new diodes and resistors on the rectifier board.  I have manually traced all secondary winding wires back to the power transformer.  All of the wires are were they should be.  There was some monkey business going on, on the primary side of the power transformer, a solder bridge and a lousy attempt to change the rig to 220vac. All voltage readings (13.5vdc, -100vdc and 160vdc) are fine except the 600vdc. I have unsoldered the 240vac lines from the rectifier board and measured the outside wires, still 0 ac volts but I get the 247vac between ether outside wire and the center tap.  I did take an ohm reading across the 240 to 240 leads.  No shorts and reading a few ohms like 0356 ohms (I don't remember the exact amount).  Also the diagram shows the 240vac center tap going to a pare of electrolytic capacitors and resistors across them instead of going directly to ground.  That line coming off between the 2 electrolytic capacitors is supposed to have 300vdc at that point.  It has 223vdc.  All this voltage readings are in receive mode.

Steve


 
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KC4MOP
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« Reply #5 on: July 11, 2013, 03:52:39 PM »

I'm thinking that some loser was really jerking that PA final to death and destroyed the tubes and probably put a 20 amp fuse in the primary and continual abuse may have damaged the power transformer. OR someone actually attempted to shoot 220vac to make it put out more power and ...pooof! Gone! Sounds like the transformer windings are shorted out inside. If you bought it as-is then you have a big problem on your hands. I can not make other suggestions. There was another here who was interested with a reply, he might have another thought. It just doesn't read like good news for that poor radio.
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KE3WD
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« Reply #6 on: July 11, 2013, 04:28:36 PM »

...I have unsoldered the 240vac lines from the rectifier board and measured the outside wires, still 0 ac volts but I get the 247vac between ether outside wire and the center tap.  I did take an ohm reading across the 240 to 240 leads.  No shorts and reading a few ohms like 0356 ohms (I don't remember the exact amount)....


Reading that 247V between each outside wire and center tap should mean that there is twice that on the two outside leads.  

By chance, is your voltmeter on a scale low enough to read 250V but not high enough to read twice that and therefore not reading the higher voltage?   A DMM might read dashes then, or? 

« Last Edit: July 11, 2013, 04:30:55 PM by KE3WD » Logged
KC7BYP
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« Reply #7 on: July 11, 2013, 04:55:58 PM »

I have a fairly new digital vom Ideal model 61-340.  You were right on the vom range setting. I am now getting 502vac on the 2 outside leads but still 0 dc output on the 600vdc line.  The 600vdc line has all new diodes and resistors installed on the rectifier board. And i dbl checked the polarity of the diodes again. They are installed right.

Steve
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KE3WD
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« Reply #8 on: July 11, 2013, 06:48:10 PM »

The "600"V being measured could be above whatever the range on the meter can read and here we go again...

Typically there will be a higher DC range, you might just move to just past the rectifiers, like at the filter cap, and measure the DC.  If the DC is fine, then the AC is nothing to be concerned about. 
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KC7BYP
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« Reply #9 on: July 11, 2013, 07:12:30 PM »

I also when up line and checked the voltage there.  There is nothing,  0 volts on the 600vdc line.  I checked the vom's manual it can handle up to 1,000 volts ac or dc providing I have the right high voltage prob.  But I am not testing anything like an old tv that needs the high voltage prob.  I have again gone over the rectifier board with the vom and a magnifying glass.  I can't find anything wrong with the rectifier board.


The "600"V being measured could be above whatever the range on the meter can read and here we go again...

Typically there will be a higher DC range, you might just move to just past the rectifiers, like at the filter cap, and measure the DC.  If the DC is fine, then the AC is nothing to be concerned about. 
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GW3OQK
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« Reply #10 on: July 12, 2013, 01:11:07 AM »

I have an FT101ZD. Some tracks were broken underneath a power pcb, open circuiting some connections. I traced with ohm meter and bypassed on the top side with wires. Sounds like that may be your trouble.

I DO NOT LIKE the 900v being present all the time its on, even with heaters off, and the 900v takes a long time to decay.

Andrew
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KC7BYP
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« Reply #11 on: July 12, 2013, 01:30:56 AM »

What do you mean by a "broken track underneath a power pcb"  and bypassed what on the top side?  The finals compartment on any tube radio is no place to be jary rigging anything when you have those kinds of high voltages persent.

Steve

I have an FT101ZD. Some tracks were broken underneath a power pcb, open circuiting some connections. I traced with ohm meter and bypassed on the top side with wires. Sounds like that may be your trouble.

I DO NOT LIKE the 900v being present all the time its on, even with heaters off, and the 900v takes a long time to decay.

Andrew

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G3RZP
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« Reply #12 on: July 12, 2013, 03:05:37 AM »

There's a lot to be said for the old fashioned VOM when working with these voltages and RF. Bring out the Simpson in the US or the AVO in the UK!
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KC4MOP
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« Reply #13 on: July 12, 2013, 03:40:23 AM »

What do you mean by a "broken track underneath a power pcb"  and bypassed what on the top side?  The finals compartment on any tube radio is no place to be jary rigging anything when you have those kinds of high voltages persent.

Steve

I have an FT101ZD. Some tracks were broken underneath a power pcb, open circuiting some connections. I traced with ohm meter and bypassed on the top side with wires. Sounds like that may be your trouble.

I DO NOT LIKE the 900v being present all the time its on, even with heaters off, and the 900v takes a long time to decay.

Andrew

He's talking about the traces on the circuit board, where the diodes are located. The power supply PCB. If there were overloads from operator error or failing tubes, it may have actually burned a trace open... Sorta like a fuse. If these terms are unfamiliar google printed circuit board. A resistor may have opened up that is preventing the HV from being distributed to the finals. I hope you did spring for some new finals for that TX.
And I keep an old RCA Senior Volt ohmist around for the HV stuff. I have burned out countless DMM's. They are crap for fixing tube equipment.
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KC7BYP
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« Reply #14 on: July 12, 2013, 05:56:09 AM »

I understand what you mean by a pcb now.  I had one of those senior moments earlyer tonight.  The rectifier board is fine.  I have been over the board with a fine tooth comb, a magnifying glass and a vom many times. There is no breaks in the foil paths.  And no solder bridges.


Steve
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