Ferguson FV33H VCR - continuing PSU issues with this

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

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

Thanks RTB, you're a star

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

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.

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

I know pdfs cannot be uploaded on here Chris ,I read the FAQs

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.

Ah-Ha me understand now

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.

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.

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?

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.

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.

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 ), 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.

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

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.

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.

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.

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.

I wouldn't say crude or nasty, just nice and simple , 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.