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Ferguson FV33H VCR - continuing PSU issues with this

 
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Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Thu Aug 02, 2012 12:16 am

This machine has no power. It's a Ferguson version of the JVC HRD-750 (an early NICAM machine, around 1989/1990).

I have tried replacing R9 (100Ohm pot), and have managed to get it to 103Ohms. I have also done C13 & 14, as well as a few other caps for which I had the same (or an acceptable alternative value) in my collection. It's also needed a "jump" wire to bypass a broken PCB track (melted by my sol. iron).

After replacement of the pot, it flashed into life for about half a second and then went dead again. And then after replacement of C13 and 14, something in the PSU began arcing (making a "zap, zap, zap" sound) and then went dead again (hopefully not a chip or transformer!) It seems it's not being awoken without a fight, then.

Unfortunately, being the numpty I am, I've taken out R1 and R6, as they both measured way under their printed values, and forgot to check which one went where before I took them out. Does anyone know which one goes where? One is printed as 2.2KOhm, the other 0.39. I don't have the service manual or diagram.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Thu Aug 02, 2012 12:27 am

I may have the FV33 manual, I will have a look tomorrow for you (evening).

The zapping sound can be caused by arcing from a track running near to where the metal shield/heatsink screws on to the PCB and the Chopper IC, I am almost certain I have had to cut a piece of track out and replace it with an insulated wire on this machine before.

If left arcing the chopper IC can fail, taking out the parts you have already mentioned.

STR10006 chopper chip IC1 S/C
39V zener diode D25 S/C
R9 O/C

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Thu Aug 02, 2012 12:40 am

Yes Aidan,
I have the FV33H manual,

Give me a moment to scan the PSU diagram, and I will post it for you.

R1 is 2.2 ohm
R6 is 0.39 ohm

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Thu Aug 02, 2012 12:55 am

Thanks RTB, you're a star :thumbr:

I'm getting the restoration bug - I will not give in until it has awoken and played a tape faultlessly! :=D

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Thu Aug 02, 2012 1:07 am

I have scanned the Diagram, but when reducing the filesize within the forum limits it is too poor to read.

Aidan I have sent you a PM.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by crustytv » Thu Aug 02, 2012 9:29 am

Just for info

PDF attachments are not allowed in the forum anyway, only photo's. We have the Technical Library for service data which keeps it all in one centralised space. It is all explained in here viewtopic.php?f=45&t=1354&p=10436#p10436

Regards
Chris

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Thu Aug 02, 2012 12:15 pm

I know pdfs cannot be uploaded on here Chris :thumbl: ,I read the FAQs :=D

I tried to upload as Jpegs and tried PNG, but the glossy Videostar manuals are not the easiest to scan at the best of times, by the time I reduced the filesize to a size the forum would accept, it was virtually unreadable.

I did end up sending it to Aidan in Pdf form in the end via e-mail. :thumbl:

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by crustytv » Thu Aug 02, 2012 12:23 pm

Ah-Ha me understand now :thumbl:

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Tue Aug 21, 2012 9:29 pm

Some voltage tests made revealed right away that the junction of R1 (2.2K) after the diode bridges (10E6 diodes) and C9 (100/400 in the circuit diagram) is low, at 30V, when it should be 132V.

I'm suspecting loads of components, but my main suspects are the ceramic caps and the choke LF1 on the primary side.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Refugee » Tue Aug 21, 2012 10:08 pm

You might have put the wrong resistor in R1.
Look at what Red to Black said in a post a few messages back.
It sounds like it should be 2.2 ohms.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Sun Aug 26, 2012 6:48 pm

Hi Refugee, I did put the correct resistor in the right place, as I took the (numerical) value printed on the side and put it back in its slot.

This resistor's value was way under, despite what it stated on its side, but even before that point in the circuit, the voltage was way down (by 100V) on what it should be (132V).

I've heard bad things about these SMPSUs in the FV30 series, both at the time (1990 editions of Television mag) and even today (a discussion on DigitalSpy forums), s it sounds as though people still haven't got over them.

I have heard that these PSUs can be very over-sensitive to even the slightest ripple in voltage, would larger value smoothing capacitors help sort this over-sensitivity?

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Refugee » Sun Aug 26, 2012 9:31 pm

Red to Black does say that he checked on a circuit he had scanned.
I was thinking you had taken a letter R with a little bit rubbed off and read it as K.
It is an easy thing to do with components that have been in service for a while.
Valves are well known for this but we are blessed with being able to peep in at the internal structure as a double check.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Mon Aug 27, 2012 2:12 pm

Hi Aidan,

R1 should be 2.2 Ohms, this is the feed resistor from the main block to the PSU, so if you have replaced it with a 2K2 resistor then no wonder you are getting low voltages.

R9 should be a 100 ohm pot, this may be marked as 101, measure this on the two outer legs, I noticed on the other forum you said you could only find a '103' value,this would be a 10K pot and is not suitable, but do double check by measurement.

R6 should be 0.39 Ohms, check again by measurement.

I hope this helps,

Ps. I have tried to optimise the filesize of the Jpeg (again), apologies in advance if this is unreadable.
Attachments
FV 33H PSU-.jpg

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Mon Aug 27, 2012 2:51 pm

AidanLunn wrote:I've heard bad things about these SMPSUs in the FV30 series, both at the time (1990 editions of Television mag) and even today (a discussion on DigitalSpy forums), s it sounds as though people still haven't got over them.

I have heard that these PSUs can be very over-sensitive to even the slightest ripple in voltage, would larger value smoothing capacitors help sort this over-sensitivity?


The PSU's you are referring to here were the Thomson designed FV30, FV31, and FV32, (the unholy trinity :=D ), these were nasty and difficult to repair.

The FV33H on the other hand was a JVC design, and was a much, much simpler affair (a lot less components), and was fairly stable and reliable, the main problem being the arcing to the heatsink, and consequent failure of the STR chip and the components already mentioned (caught in the crossfire). They were relatively easy to repair, unlike the three Thomson designed ones mentioned above.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Sun Nov 25, 2012 10:48 pm

After a few months, I have come back to it

Replaced the STR10006 chopper - still nothing.

I did notice that one of the ends of the heatsink for the STR10006 has some signs of arcing - I believe the chopper heatsink shorting to the diode bridge was common on these?

I have not replaced the mains smoothers and those two resistors yet, so they'll be next within a few weeks (once I've been paid!)

RTB, you have a PM re: the PSU service diagram, as I've lost my print of the original.

EDIT: don't need it, just seen the above post

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Wed Jul 30, 2014 4:03 pm

As part of my gaining experience with diagnostics and circuit theory with Refugee's help, I decided to bring this VCR down to him. It still has the same symptoms

When the VCR is powered up, we can hear the STR chopper beginning to oscillate but then cutting out. "Refugee" suspects a short circuit somewhere in the PSU, that is still present when there is no load on the PSU.

The mains transformer in this unit is of a black Mitsubishi type, whereas "Refugee" said usually machines of this generation had different coloured transformers from Mitsubishi.

We have tested around the PSU, the starter cap is holding charge but there is no load placed on it after the first second or so. It is looking increasingly likely that the transformer itself does have a short. On my next visit date, I will be bringing down my HRD750 to swap test the PSUs at his suggestion.

The PSU has numerous deep cracks in the board that have been fixed, and as far as we can tell, these have all been patched up on the copper tracks.

We are supposed to be dealing with radios first, but I knew my diagnosis techniques on this machine were wrong completely, so I had the idea of bringing this machine down to him to teach me diagnostic methods when it is a known component fault.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Refugee » Wed Jul 30, 2014 4:39 pm

How the power supply starts is that there is a potential divider with a capacitor tapped off it that will be discharged at switch on. This kick starts the 3 transistor oscillator.
There is a leaky short that is killing the oscillator before it goes to a hard short so no cold testing will find the fault.
There is no control chip in this one. There is also no opto coupler either.
The next step will be to isolate one end of each diode and test it on a bench power supply.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Wed Jul 30, 2014 7:49 pm

This PSU is fairly well behaved, there no hidden surprises other than one of the pins of the STR chip can flash across to the grounded heatsink PCB track (I think it was pin 3 ) , almost all faults can be found with cold checks for either short or open circuit components, I have never had a chopper transformer fail on this model.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Wed Jul 30, 2014 8:04 pm

I should add that when this machine was delivered to me, it had evident signs of being treated like a football by someone in Royal Mail. The right side of the front panel is missing one of its "hooks", so that is a bit loose, but also the PSU had cracks in it, by no coincidence, this is also on its right hand side. It's either a short somewhere or more superficial damage to the PSU block.

"Refugee" hyas said that although it is clearly a reliable design, it's still very crude and nasty. I can't comment either way as i haven't had enough experience on PSUs of any kind to make any opinion of mine worth taking notice of.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Wed Jul 30, 2014 8:12 pm

I wouldn't say crude or nasty, just nice and simple :qq1 , this PSU used very rudimentary primary regulation merely to provide voltage step-down and multiple supplies, similar to a conventional mains transformer except it was lighter in weight.

The main regulation action was carried out on the secondary side via an STK chip in similar fashion and convention to the earlier machines of this series with conventional mains transformers, this PSU was evolutionary rather than revolutionary and in keeping with JVC designs of the period being a step-change design.

Later SMPSUs dispensed with the secondary regulator apart from the odd one or two fixed voltage types, these used a much more tightly regulated SM part with the added circuit complications, power control etc.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Refugee » Fri Aug 01, 2014 11:28 pm

We have had the board out on the bench and This time the diodes were on test at currant limited 9 volts.
I have now found a 39 volt zena diode that is not totally short circuit so that it got past the DMM check but did not hide form this new check.
The VCR is now awaiting spares for the diode.
It looks like this part is fitted to stop the unregulated output of the power supply from rising too high when the VCR is set to standby. It is across a 30 volt supply rail.
This diode will have a hard time if standby is active for long periods of time.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Red_to_Black » Sat Aug 02, 2014 4:58 am

I don't think being in standby makes any difference with this PSU Ref, or very minimal difference.

It is basically a fixed output as far as the primary regulation is concerned, it has only one feedback loop and this is on the primary side, the output voltages are set according to the winding ratios of the chopper transformer, and while not as tightly regulated as more sophisticated SMPSUs with multiple feedback loops and monitored secondary rails it does give much better output regulation than a conventional mains transformer would with light loading, IOW the outputs won't rise by very much due to no/light loads.

Also there is no power control/stby switching etc. on the switch mode part, this function is carried out in the secondary STK regulator post Switched mode part.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by sideband » Sat Aug 02, 2014 7:11 am

They don't make 'em as simple as this anymore! Apart from the odd STK failure, most problems I had with these were on the secondary side. A quick run-through over the diodes with a testmeter invariably located a shorted diode. Not sure if there are any circuit protectors on this one but they look like two-legged transistors. Worth just checking any of those if fitted.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by Refugee » Sat Aug 02, 2014 8:05 am

The zena is across the 30 volt rail that goes to the clock so the actual rail only has a small load anyway.
It is likely that the clock will dim slightly when the unit is taken out of standby as the supply will rise a little bit in standby and this rail with a small load all the time does not go to the main regulator. The fuses are on the main board by this regulator.
It has taken a while to fix as there are quite a few bits that have already been changed a couple of years ago and some cracks in the power board that have had to be fixed.

 
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Re: Ferguson FV33H VCR - continuing PSU issues with this

Post by AidanLunn » Fri Aug 08, 2014 10:00 pm

We have life on the display panel! D25 was s/c. Replacing with a 30V and 10V in series, as no 39V to hand, cured the fault!

The only other electronic fault now is that the idler motor has no power. This has been traced down to CP804 being o/c.

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