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JVC HRD-725 PSU problem.

 
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JVC HRD-725 PSU problem.

Post by AidanLunn » Sat Mar 28, 2015 9:02 pm

Hello all

My next "repair" project on my list or repairs to clear before my next restoration brings me to this VCR.

The problem: Whenever switched on from the mains switch, even if the on/off button is "out" (i.e. off), the machine switches on fully for 8 seconds, then goes to standby. It won't obey any commands from the front panel whatsoever apart from the on/off and timer buttons. Whenever the timer button is switched in then back out again, the machine stays on for 8 seconds, then goes to standby.

Diagnosis so far:
I've established all rails from the collector of Q3 are missing, voltage at collector being 0.2V. The base and emitter are all OK (although base slightly high at 12.7V). The voltage on the collector of Q8 is 12.7V!

Before I noticed the collector voltage of Q8 I tried:
1) Disconnecting all of the plugs to other boards from this in case there was a short circuit on another board. No difference. So that isolated the fault to the regulator board. The voltage on the base and emitter of Q3 isolated the fault to anything on the collector side.
2) Disconnecting C16 and IC2 (9V regulator), to rule anything out between c16/IC2 and CN5 - no difference.
3) I've tried replacing Q3 in case it was faulty - no difference.
4) I tested D3 & D19 - both OK

Then I noticed the voltage on the collector of Q8 - 12.7V! (Surely it's a balls-up at the printing works - maybe there's a red "1" hidden behind that collector lead-in on Q8, so maybe it should be 10.8V? That's what it seems, looking at the base of Q3 and the pin 10 voltage on CN6.)

So then,
5) I tested D6 - OK
6) D12 (this is tapped into the 12V rail going to the emitter of Q3) - OK.

As it stands, the missing voltages are:
CN1 pin 1
CN5 pins 1&2 (pin 1 at just 2V)
CN6 pins 5, 6 & 7
CN6 both OK
CN3 pin 3
CN4 all OK
Attachments
Image (277).jpg

 
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Re: JVC HRD-725 PSU problem.

Post by Cathovisor » Sat Mar 28, 2015 9:07 pm

Aidan,

can you please post diagram pictures in PNG/GIF format ONLY - as JPEGs they become virtually illegible, as this one is.

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Sat Mar 28, 2015 9:24 pm

If this machine is the one where the PSU is made up of two separate boards, with the regulators on a separate PCB, then dry joints on the wire links that connect the two PCBs cause all manner of weird and wonderful symptoms.

Looking at the poor diagram above, the root cause appears to be a loss of the switched 12V rail, the other missing voltages being derived from that SW 12V rail.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Sat Mar 28, 2015 9:53 pm

I've just noticed the poor quality.

Hopefully this one is better. I've battled with software on my PC that just can't compress the image down to the required size adequately, so I've uploaded it to an image sharing site. Not ideal I know, but I've just given up on trying to compress them adequately. Even scanning, compressing and saving in PNG and GIF at every stage made not much difference (so no stage in anything but PNG or GIF).

Image

http://tinypic.com/r/4hxthh/8 has a higher resolution version (click on the image on there)

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Thu Apr 02, 2015 9:32 pm

I've tested CN6 again - pins 5, 6, 7, 9 & 10 are missing. The lack of the latter two is presumably down to the lack of an swd5v rail into the CPU.

There are no dry joints on the wire links at all.

So with everything disconnected from the collector of q3, including C16 and ic2, and a replacement of q3, I am still no further forward and the collector of q3 is still around 0.5V. Even diconnecting the plugs results in a voltage change of about .2V.

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Thu Apr 02, 2015 10:16 pm

Hi Aidan,

The switched supplies, SWD 5V SWD 9V and SWD 12V will not appear from the PSU until it gets the "OPERATE ON" signal from the mechacon on CN6 pin 10. Under normal circumstances pressing the operate button causes 7.7 V to be applied to pin 10, this should then cause Q8 to conduct heavily which then turns on Q3 and Q5 via diode pack D6.

Sorry I no longer have any manuals, you will need to trace where CN6 pin10 connects to on the mechacon board.

Hope this helps.

John

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Thu Apr 02, 2015 11:20 pm

Sorry Aidan but I've just reread you first post and you say the machine comes on for 8 seconds when pressing the operate or timer buttons, are the switched voltages there during this period? If so do you seen any movement of the reels or loading motor?

This deck uses an IR optical sensor as a sort of mode switch, if yes to the above this could be the source of the problem.

John

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Thu Apr 02, 2015 11:23 pm

I wonder if temporarily shorting C-E of Q8 might help to see what is or is not present supply wise ?

It could be a mechanical fault though that is causing it to shut down after 8 seconds, so I would be a bit wary of running it like this with the PSU connected to the rest of the machine, but it may help pin down whether the fault is in the PSU/Regulator itself or further on in the machine.

This machine is the JVC equivalent of the Fergy 3V43, and I don't have the manual for this one either as far as I have looked, I might have a manual put away somewhere but I somehow doubt it, I keep what remaining manuals I have together, I will have another look over the weekend though.

Edit: just seen your other post Jayceebee, and I was also thinking on the lines of a possible mechanical type fault. :thumb

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Thu Apr 02, 2015 11:38 pm

Hi R2B, it does sound as though the mech cannot find the unload position possibly caused by the sensor or possibly even the grease on the loading assembly has turned to glue.

Aidan, with the power off wind the loading motor by hand so that the guides travel half way towards the load position. Apply power and see if the guides try to return to the unload position, if they do but the loading motor keeps on going then the sensor is suspect.

John.

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Thu Apr 02, 2015 11:45 pm

jayceebee wrote:Hi R2B, it does sound as though the mech cannot find the unload position possibly caused by the sensor or possibly even the grease on the loading assembly has turned to glue.

John.


Without a manual I wasn't quite sure which actual deck was fitted to this machine, I can remember the earlier machines such as the 3V16, 22,23,29, 30,31 and 32 etc. but the other 3V models are just a blur now.

I have about a dozen old Thorn manuals left and couple of the later FV series but that is about it, I would recognise the machine internally if I had it in front of me though :cca

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Thu Apr 02, 2015 11:52 pm

The mech is almost identical to that used in the 3V44, 3V45/8947, 3V48 models, similar carriage as the 3V35/8944 with the twin flaps but the machines were half the height.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 12:08 am

Red to black wrote:
jayceebee wrote:Hi R2B, it does sound as though the mech cannot find the unload position possibly caused by the sensor or possibly even the grease on the loading assembly has turned to glue.

John.


Without a manual I wasn't quite sure which actual deck was fitted to this machine, I can remember the earlier machines such as the 3V16, 22,23,29, 30,31 and 32 etc. but the other 3V models are just a blur now.

I have about a dozen old Thorn manuals left and couple of the later FV series but that is about it, I would recognise the machine internally if I had it in front of me though :cca


JCB is correct, it's the deck that came before the one with the separate idler motor.

I'll carry out everything suggested when I'm next with it but I feel I shoukd mention (as has been asked) that there is not a peep of life in the mechanism whatsoever, the carriage won't even detect pressure applied to it. All plugs are in the correct places etc.

It's strange. Like vintage tellies I enjoy using a well-built VCR. Unlike tellies working on said VCRs drives me nuts (same with any solid state tech, really!)

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Fri Apr 03, 2015 12:09 am

jayceebee wrote:The mech is almost identical to that used in the 3V44, 3V45/8947, 3V48 models, similar carriage as the 3V35/8944 with the twin flaps but the machines were half the height.

Thanks,
I found a paper JVC HRD455 manual, which is the Thorn 8945 equivalent :bba this appears to have the same PSU and regulator, I will have a look at the deck in this manual. :bba

A quick internet search showed up a thread on UKVRR http://www.vintage-radio.net/forum/show ... hp?t=76824 by Aidan which I replied to in 2011, I wonder if this is the same machine ?

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 12:12 am

Red to black wrote:
jayceebee wrote:The mech is almost identical to that used in the 3V44, 3V45/8947, 3V48 models, similar carriage as the 3V35/8944 with the twin flaps but the machines were half the height.

Thanks,
I found a paper JVC HRD455 manual, which is the Thorn 8945 equivalent :bba this appears to have the same PSU and regulator, I will have a look at the deck in this manual. :bba

A quick internet search showed up a thread on UKVRR http://www.vintage-radio.net/forum/show ... hp?t=76824 by Aidan which I replied to in 2011, I wonder if this is the same machine ?


It is the same machine, something has clearly happened to it in the intervening time where it has lain dormant because it was showing more signs of life then than it is now.

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Fri Apr 03, 2015 12:27 am

Don't worry about the carriage at this point, the mech will always attempt to get to the unload position if it isn't already there when powered on. The fact that it isn't means either no power to the loading motor or it's driver circuit due to a blown fuse, CP or possibly a logic problem in the mechacon, no common faults here that spring to mind.

Hopefully R2B can post some snippets from the circuit diagram which will help, electronic faults here were few and far between.

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Fri Apr 03, 2015 12:33 am

Actually the diagram in the HRD455 manual has two PSU diagrams, one of them is identical to the one posted by Aidan earlier in this thread, however this is for the "A" version and is not for the UK it uses a 110V transformer.

The second diagram is the "EK" version (ie. UK) and differs quite a bit from the one posted.

I don't know if the one posted earlier is actually the correct one for the machine or not ?

It is possible JVC have mixed and matched versions, could you confirm this please Aidan ?

Also if this is the machine from 2011 we are likely to be facing multiple faults, one of which is man made after re-reading the thread on UKVRR.

If Aidan cannot confirm that the earlier diagram is correct or not, I will attempt to scan both versions I have here, I don't want to confuse anyone unnecessarily but it would be helpful if we had the correct drawings to give us a sporting chance.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 9:57 am

Red to black wrote:
If Aidan cannot confirm that the earlier diagram is correct or not, I will attempt to scan both versions I have here, I don't want to confuse anyone unnecessarily but it would be helpful if we had the correct drawings to give us a sporting chance.


Yes, the one I posted earlier is for the 725.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 3:18 pm

Just before I inspect what RTB & JCB have suggested, I thought I'd examine the voltages on IC204 (CPU)

Most are fine, but here's what I found on pins 1-5:

1: 9.5V (OK)
2: 9.48V (should be near 0)
3: 9.48V (OK)
4: 0V (Should be 9V)
5: 9.2V (Should be 0V)

I unplugged CN204 in case these erroneous voltages, particularly on pins 2 and 3, were down to the sensors.

When unplugged pins 2 and 3 were both 0.7V - surely nothing apart from a short in IC204 would cause these two pins to have the exact same voltages as each other no matter if CN204 is plugged in or unplugged?

I can't see any other way for pin 2 to directly reflect the voltage on pin 3?

Image

Here is a direct link to the part of the Mechacon diagram concerned for a closer look at the diagram.

http://oi57.tinypic.com/2hn6j40.jpg

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Fri Apr 03, 2015 3:20 pm

AidanLunn wrote:
Red to black wrote:
If Aidan cannot confirm that the earlier diagram is correct or not, I will attempt to scan both versions I have here, I don't want to confuse anyone unnecessarily but it would be helpful if we had the correct drawings to give us a sporting chance.


Yes, the one I posted earlier is for the 725.


Looking at Thorn equivalents the manual I have for the JVC HR-D455 suggests it is the equivalent to the Fergy 3V42 this may be near enough.

Aidan I would again strongly suggest you check your diagram for the regulator/PSU version you posted earlier.
The identical one in my manual to the one you posted earlier is only used on the Canadian/US version of the HR-D455/3V42 the UK version for the same model has significant differences and component location numbers. I cannot see the 3V43 using the US version of the 3V42 PSU regulator. It might help if we could see the transformer mains input bit on your diagram.

It is possible I suppose that JVC has used the US/Canadian regulator from the 3V42 with a European mains transformer on your 3V43 model, it just seems a bit of an unlikely coincidence in my opinion, although I will stand to be corrected.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 4:03 pm

Red to black wrote:
Aidan I would again strongly suggest you check your diagram for the regulator/PSU version you posted earlier.
The identical one in my manual to the one you posted earlier is only used on the Canadian/US version of the HR-D455/3V42 the UK version for the same model has significant differences and component location numbers. I cannot see the 3V43 using the US version of the 3V42 PSU regulator. It might help if we could see the transformer mains input bit on your diagram.

It is possible I suppose that JVC has used the US/Canadian regulator from the 3V42 with a European mains transformer on your 3V43 model, it just seems a bit of an unlikely coincidence in my opinion, although I will stand to be corrected.


Definitely the correct one, the mains input says "AC 240V 50/60Hz"

Image

http://oi62.tinypic.com/14ce103.jpg

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Fri Apr 03, 2015 4:18 pm

Thanks for that,
Sorry if I keep banging on about this point, just in view of the machines fault history :qq1 I would want to confirm that the PSU is operating correctly standalone first before getting deeply involved with the Syscon circuitry.

On my diagram (which I need to scan still) the switched rails differ slightly, and this is important, if this is wrong then we have no chance.
Some machines have a SW 12V rail to the mode switch whilst others have a SW 9V, there are also other slight differences.

If I can get a reasonable filesize and a decent scan (difficult) I will still post up, then others can also see, I will also trawl through the remaining Thorn and JVC manuals I have to see if I can find a better match.

I need to take the hound for a walk first, then I will attempt to scan when I come back. :cca

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Fri Apr 03, 2015 4:35 pm

Aidan are all the switched supplies present during the 8 second period when you press the "ON" button and does the LED on the button light if it has one. This is very important, start with the basics first.

John

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 4:42 pm

Red to black wrote:Thanks for that,
Sorry if I keep banging on about this point, just in view of the machines fault history :qq1 I would want to confirm that the PSU is operating correctly standalone first before getting deeply involved with the Syscon circuitry.

On my diagram (which I need to scan still) the switched rails differ slightly, and this is important, if this is wrong then we have no chance.
Some machines have a SW 12V rail to the mode switch whilst others have a SW 9V, there are also other slight differences.

If I can get a reasonable filesize and a decent scan (difficult) I will still post up, then others can also see, I will also trawl through the remaining Thorn and JVC manuals I have to see if I can find a better match.

I need to take the hound for a walk first, then I will attempt to scan when I come back. :cca


That's fine, thanks for your help with this JCB & RTB.

But pin 2 of IC204 reflecting pin 3 like for like still has me bugged! And then pin 4 and 5 the opposite of each other.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Fri Apr 03, 2015 4:48 pm

jayceebee wrote:Aidan are all the switched supplies present during the 8 second period when you press the "ON" button and does the LED on the button light if it has one. This is very important, start with the basics first.

John


No they're not.

A detailed description:
This machine has two lights for power - a "POWER" light that is on all the time whenever a mains input is present, and an on/off light on the push button itself - it's a spring loaded on/off button, not a touch sensitive one, but in this case, you can switch the machine on from the mains, with the power button out (in the off position) and the machine still starts itself up fully. The light on the button itself is constantly extinguished. You can then press the button no matter how many times in that 8 seconds, the machine ignores it. Same goes for the "timer" button - this switches on the flashing "timer" indicator on the LCD panel, but doesn't switch it off by itself.

If the machine then goes off by itself but you have the timer button pressed in or out, pressing it will turn it back on for 8 seconds. Same goes for the power on/off button.

ETA: the machine obeys commands like channel change, counter reset etc, but as there is nothing in the cassette carriage, I can't test if the tape operation buttons are obeyed or not. Pressing any of these does not delay the time until switch-off, you could keep pressing the channel up button for those 8 seconds, it still goes off at 8 seconds.
Last edited by AidanLunn on Fri Apr 03, 2015 4:51 pm, edited 1 time in total.

 
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Re: JVC HRD-725 PSU problem.

Post by Refugee » Fri Apr 03, 2015 4:50 pm

That 8 seconds sounds like a time out by the processor waiting for the mode switch to show the mech in the ejected position.
Try rotating the loading motor by hand towards the eject position and see if it stays on once it gets there.

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