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Old 24th Oct 2017, 5:19 pm   #1
G0BHU-Mike
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Default FT101ZD Power output issues

Hi,
My FT101ZD MKIII is suffering severe “HT Voltage sag” <> 50% on PTT. I have replaced the Rect ‘B’ board and both PA and Driver boards. Problem does not change. Notably, if the 12BY7 is removed the voltages do not Sag. I have replaced both 6146’s and 12BY7 - no significant change.

Observation - I note that there are two differing Grounds (earths)? Chassis earth and transformer ‘0’ (shown on diagram as the same earth). The cct diagram does not differentiate them?? When connected together disaster happens (I destroyed at least one if not both 6146’s) - replaced both with new ones. My problem is I cannot see a dc HT return path to the rectifiers for the Screens and driver HT. Also the transformer HT ‘0’ volt shows it should be at earth. But the above catastrophe happens if you do this.

The voltage sag seems to be related to a no DC return to the rectified HT supply. A scope shows a very large 50Hz rectifier hum with the RF on top of it. Importantly I get power output before the voltage sag.

Has anyone experienced this? Any suggestions would be great fully received.

Thanks
Mike - G0BHU
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Old 27th Oct 2017, 8:46 pm   #2
Bazz4CQJ
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Default Re: FT101ZD Power output issues

Cannot offer any specific help, but I wonder if you are aware of the series of articles on the 101 written by Harry Leeming in Practical Wireless many years ago. I think Leeming had worked for the original UK importer for Yaesu and knew the sets, and all their quirks, backwards. I would have guessed that they are 'Must haves' for an owner of a 101.

B
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Old 27th Oct 2017, 8:50 pm   #3
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Default Re: FT101ZD Power output issues

If you connect the two earths together and disaster happens, this suggests that one earth isn't an earth. Have you checked the resistance between them with the power off and the volatge between them with the power on?

Can you post a portion of the circuit diagram please.
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Old 27th Oct 2017, 9:06 pm   #4
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Default Re: FT101ZD Power output issues

Presume you are switched to transmit when this drop occurs, what mode and what current is drawn when the voltage drops?
That is, is it excessive current being drawn or a high impedance supply?
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Old 27th Oct 2017, 9:13 pm   #5
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Default Re: FT101ZD Power output issues

The FT101Z has the ability to melt down if you get a minor open circuit on the pot that sets the bias voltage to the valves. After having this problem I fitted fixed resistors to ensure that an open circuit is fail-safe.

By the way, just because the PA has been "shorting the mains" with spectacular results doesn't necessarily mean they are dead. I found that mine recovered after a while - I suspect that excess heat boils vapours out into the vacuum and these are gradually removed by the getter, restoring the valves to normal operation eventually.
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Old 28th Oct 2017, 2:25 am   #6
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Default Re: FT101ZD Power output issues

Re Harry Leeming, he has (had?) a column in Practical Wireless called "In the Shop", which started in June 2006 (bi-monthly column).

Haven't seen a recent PW so not sure if it is still going, but there is plenty of info re older Yaesu rigs and repairs etc.
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Old 28th Oct 2017, 5:35 am   #7
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Default Re: FT101ZD Power output issues

Harry Leeming is perhaps the single most knowledgeable chap on Yaesu radios, and has very generously distributed his knowledge. His articles are worth tracking down and collecting.

The FT101Z and FT101ZD are not lineal descendants of the earlier FT101 models. There are major differences. They are simplified derivatives of the FT902DM. So information about the earlier FT101 series doesn't help with a Z or a ZD.

David
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Old 28th Oct 2017, 8:53 am   #8
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Default Re: FT101ZD Power output issues

Is this the 900 volt line that is dropping? The 900v circuit uses a voltage doubler, the centre tap of the transformer winding is not connected to anything.
If there is no overheating when the voltage drops it would indicate a high impeadance supply, the 900 volt line is on the Rec A board on the circuit I have downloaded. There are very few components in the 900v doubler circuit and a diode and capacitor located off the board, circuit designation 200.

I have never worked on one of theses, just looking at the circuit.

The voltages are very high, extreme caution is required in servicing this rig.
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Old 28th Oct 2017, 10:53 am   #9
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Default Re: FT101ZD Power output issues

Harry Leeming is still in PW and worth an email.
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Old 28th Oct 2017, 1:19 pm   #10
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Default Re: FT101ZD Power output issues

I've visited Harry's shop a few times when he was in business, and bought equipment from him... a very nice bloke indeed.

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Old 16th Nov 2017, 10:13 pm   #11
G0BHU-Mike
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Default Re: FT101ZD Power output issues

Hi Not very good at using this means to communicating. Apologies for the delay.
Moderator - not sure how to get a snap shot of the relevant part of the diagram (on an iPad) As the diagrams are all independent of each other - takes some studying. I Lost all i wrote on my last attempt.

I think a line to harry is a very good Idea - thanks to all who suggested it. Unfortunately pride has so far overridden common sense!
Does anyone know how to contact him or perhaps his email please?

Nuvistor - 900v issue - yes it is - and this side is OK Tks. I found this unit needed bleeder resistors and doesn’t have the PCB talked about. They are now fitted. As is the safety resistor on the PA neg Bias supply (Tks GMB). Don’t want to loose another set of bottles. and thanks I will check the valves later - i’vê not scuttled them.

FYI I do have a lot of experience on very high voltage Comms equipment thanks - but your warning is well received and i concur your cautions.

Current drain looks normal its in the 0.1 to 1ma range (as you’d expect on screens). Maybe this is too much Interestingly the ac voltage at the transformer hardly drops at all - it all seems to happens at the valve sceen input and here the conundrum - all the resistors check out OK’ Ive even changed the whole Rectifire ‘B’ board and both the PA and Driver boards ... but same-same I’m thinking parasitic oscillation, but not seen it on any scope - bottles don’t glow either!! No visible component destruction either. Hump! It’s such a basic circuit (except for th isolated ground and chassis issue)

StationX - not very clever here. Don’t know how to attach to this doc on an iPad. Sorry.
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Old 16th Nov 2017, 10:42 pm   #12
G0BHU-Mike
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Default Re: FT101ZD Power output issues

Hi
Now on a laptop....
Hopefully, for those interested, I have uploaded the relevant Drawings. for the FT101ZD MKIII.
Unfortunately the drwings are quite faint.
Sadly for service manual drawings, there are several badly uncorrected errors.
but that for another discussion.
Tks
Mike G0BHU
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Old 16th Nov 2017, 11:44 pm   #13
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Default Re: FT101ZD Power output issues

Quote:
Originally Posted by Station X View Post
If you connect the two earths together and disaster happens, this suggests that one earth isn't an earth. Have you checked the resistance between them with the power off and the voltage between them with the power on?

Can you post a portion of the circuit diagram please.
Correct - Yes - See my last reply - earths are different one is ‘0’v and the other is Chassis earth but the circuit dgm and all written documentation show them or say they’re earth (with the same symbol). Tks on Rx -18v, Tx -127v!!
Not sure how to attach these drawings.
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Old 17th Nov 2017, 9:07 am   #14
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Default Re: FT101ZD Power output issues

Mike.

As you're a new member your posts won't appear immediately, they'll need to be approved by a moderator. This is an anti-spam measure. depending on when you post, a post may be approved in minutes or it may take until the next day.

You'll find information on managing attachments here:-

http://www.vintage-radio.net/forum/s...ad.php?t=77650

As a general comment, your diagrams could do with being a little larger.
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Old 17th Nov 2017, 11:25 am   #15
G0BHU-Mike
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Default Re: FT101ZD Power output issues

Hi further diagram clarification: The components (capacitors) on the transformer side of the Resistors R1005, R1006 and R1010 are shown with an earth symbol but are in fact connected to the “0” or GND line at the PCB and is NOT chassis earth. ALL other earths shown are to Chassis earth, but are also shown as “GND”. Confusing. This was the reason I perceived them to be the same earth - later, PCB copper layout investigations, showed the GND’s were very different but using the same symbols and PCB printed “GND”. You might wonder why I linked them, well, a fellow ham had replaced the original cooked transformer. I have no reference position. Nothing in the User or SVC Manuals mentions they are not. Measurements of the Txfmr windings, indicate seemingly correct connections. Voltages are not exactly where they should be but seem tolerably in range. The main cct dgm shows the same earth symbol on the end of the transformer HT winding too? Sorry for this long explanation, but have been round and round this one and frankly puzzled. Anyone know how I can contact Harry Leeming?
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Old 17th Nov 2017, 3:38 pm   #16
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Default Re: FT101ZD Power output issues

The address is in some recent Practical Wireless I will look. Got it. g3lll@talktalk.net
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Old 18th Nov 2017, 11:01 am   #17
G0BHU-Mike
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Default Re: FT101ZD Power output issues

Quote:
Originally Posted by HamishBoxer View Post
Harry Leeming is still in PW and worth an email.
Thanks
I will scribble him a letter.
Mike G0BHU
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Old 18th Nov 2017, 11:02 am   #18
G0BHU-Mike
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Default Re: FT101ZD Power output issues

Quote:
Originally Posted by HamishBoxer View Post
The address is in some recent Practical Wireless I will look. Got it. g3lll@talktalk.net
Thank you
I will try this avenue too
Best 73's
Mike G0BHU
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Old 21st Nov 2017, 3:18 pm   #19
G0BHU-Mike
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Default Re: FT101ZD Power output issues

Hi all - I've managed to contact Harry. We will see if this brings any glimmers of hope.

A new observation - FT101ZD owners - the circuit diagram shows the 160v line connected directly to the 12BY7 bias supply? surely this cannot be true ? Electronically one is -33v the other+160v. Does any one have a drawing where these are not connected or is it correct as is?
Drawing below shows they're connected.
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Old 21st Nov 2017, 4:43 pm   #20
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Default Re: FT101ZD Power output issues

I can't comment on your unreadable circuit, but they are not joined together.

There is a separate output for the PA and the driver on the PSU board.
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