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JVC HRD-725 PSU problem.

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AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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

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Topic starter Posted : 28/03/2015 9:02 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

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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Posted : 28/03/2015 9:07 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

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.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 28/03/2015 9:24 pm
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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).

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

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Topic starter Posted : 28/03/2015 9:53 pm
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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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Topic starter Posted : 02/04/2015 10:32 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

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

John.

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Posted : 02/04/2015 11:16 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

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

John.

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Posted : 03/04/2015 12:20 am
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

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

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 03/04/2015 12:23 am
Jayceebee
(@jayceebee)
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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.

John.

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Posted : 03/04/2015 12:38 am
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

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

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

ReplyQuote
Posted : 03/04/2015 12:45 am
Jayceebee
(@jayceebee)
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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.

John.

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Posted : 03/04/2015 12:52 am
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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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Topic starter Posted : 03/04/2015 1:08 am
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

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 ?

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

ReplyQuote
Posted : 03/04/2015 1:09 am
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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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Topic starter Posted : 03/04/2015 1:12 am
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

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.

John.

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Posted : 03/04/2015 1:27 am
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

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.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 03/04/2015 1:33 am
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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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Topic starter Posted : 03/04/2015 10:57 am
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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?

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

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Topic starter Posted : 03/04/2015 4:18 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

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.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 03/04/2015 4:20 pm
AidanLunn
(@aidanlunn)
Prominent V-Ratter Deactivated Account

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"

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Topic starter Posted : 03/04/2015 5:03 pm
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