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JVC HRD-725 PSU problem.

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Fri Apr 03, 2015 5:20 pm

Refugee wrote:That 8 seconds sounds like a time out by the processor waiting for the mode switch to show the mech in the ejected position.


Thats right Ref, if it's not already there the mech will try to reach the unload position and then attempt eject if a cassette if inserted, if this isn't achieved within the 8 seconds the the machine shuts down to prevent damage.

If Aidan has done what I asked and manually wound the mech to the half way point the the first thing that should happen is that the switched supplies should become established and the loading motor should start to run irrespective of the position of the carriage.

Aidan, the power on signal for the PSU comes from pin51 of IC204 on the mechacon. Check here with your meter and tell us what you have during the 8 second period when the channel indicator is lit.

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Fri Apr 03, 2015 8:26 pm

3V42 USA type 01.jpg
3V42 USA type 02.jpg
3V42 UK type 01.jpg
3V42 UK type 02.jpg
Here are the scans of the two types I have for the 3V42/HR-D455, I had to scan each part twice to get all of it on my A4 scanner, the file sizes have been reduced to fit the forum.
I originally scanned them as a PNG, then as a TIFF, however the compression software converted them back to JPEGs :aab

I still have the Tiff scans available if required.

The US/Canadian PSU is shown in the first 2, the UK type in the second two (I think :bba )

 
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Re: JVC HRD-725 PSU problem.

Post by Refugee » Fri Apr 03, 2015 9:58 pm

jayceebee wrote:Thats right Ref, if it's not already there the mech will try to reach the unload position and then attempt eject if a cassette if inserted, if this isn't achieved within the 8 seconds the the machine shuts down to prevent damage.


Yes but I got the impression from Aidan that the motor was not running correctly in an earlier post.
We do need to establish that the motor is indeed running and in good order.

 
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Re: JVC HRD-725 PSU problem.

Post by Red_to_Black » Fri Apr 03, 2015 10:11 pm

Part of the trouble now Ref is cause and effect, we already know the machine had one fault, now it has others, some man-made, we are now in a classic chicken and egg situation.

It needs looking at logically and step by step diagnoses, I personally would verify the PSU is correct first, that means forcing it on while disconnected from the machine, that would be my first move and then progress from there.

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Fri Apr 03, 2015 10:18 pm

Hi Ref, what we need to do first is to get the switched rails up and running, by leaving the loading mech out of position we know it should force the "opereate" line high as soon as power is applied for 8 seconds.

Thanks for the scans R2B but unfortunately they show CN2 as only having 8 pins, Aidans show 10.

Aidan can you check that the 9v supply is permanenetly present on IC204 pin 1, it is derived from the unswitched 12v supply (which we know is present form your previous checks) via zener diode D242.

I wont be around much as I am working this weekend and Easter Monday so good luck.

John.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Sat Apr 04, 2015 2:38 am

jayceebee wrote:
Aidan can you check that the 9v supply is permanenetly present on IC204 pin 1, it is derived from the unswitched 12v supply (which we know is present form your previous checks) via zener diode D242.

I wont be around much as I am working this weekend and Easter Monday so good luck.

John.


I haven't done the other tests, but this I do know, the 9v at pin one is permanently present.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Wed Apr 29, 2015 10:27 pm

jayceebee wrote:
Refugee wrote:That 8 seconds sounds like a time out by the processor waiting for the mode switch to show the mech in the ejected position.


Thats right Ref, if it's not already there the mech will try to reach the unload position and then attempt eject if a cassette if inserted, if this isn't achieved within the 8 seconds the the machine shuts down to prevent damage.

If Aidan has done what I asked and manually wound the mech to the half way point the the first thing that should happen is that the switched supplies should become established and the loading motor should start to run irrespective of the position of the carriage.

Aidan, the power on signal for the PSU comes from pin51 of IC204 on the mechacon. Check here with your meter and tell us what you have during the 8 second period when the channel indicator is lit.


During that 8 second window, there is a big fat 0V on pin 51 of IC204.

Beforehand, I wound the mech to halfway position (previously at fully loaded position) and no difference. Tried in the no cassette position. No difference. Tried manually winding the cassette carriage complete with cassette down into the mech. No difference.

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Wed Apr 29, 2015 11:17 pm

That's not good, it means that IC204 is not turning on the switched supplies. The two 52 pin micros talk to each other with bi-directional data and a clock pulse, the operate button goes to pin 50 of the lower one (no ref on the circuit in your link, IC201 or 202?) it then sends data on pins 27,28,29,30 along with clock pulses on 31 to IC204 to command pin51 to go high.

You need to check the operate button has some effect on pin50, that there are VSS and VDD supplies on both micros along with the clock osc (pins 23 and 25 on the lower IC, suspect it may be the same pins on IC204) and also that the reset pulses are correct.

John.

 
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Re: JVC HRD-725 PSU problem.

Post by AidanLunn » Sat May 02, 2015 5:09 pm

As this thing is driving round the twist, I hope members following this thread don't mind me putting off repairing this for a while, I can see why repairing VCRs was hated by some!

I shall be returning to my natural environment of working on a late 50s valve TV for the time being.

 
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Re: JVC HRD-725 PSU problem.

Post by jayceebee » Mon May 04, 2015 8:23 pm

Hi Aidan, these were pretty complex even for domestic machines and wouldn't be the first choice as a first attempt at repairing VCR's. For anyone starting the machine I would recommend is the Ferguson 3V29/30 or equivalent, good mechanics and all the PCB's have descent accessibility.

To be honest repairing VCR's wasn't too bad but some faults could give you nightmares such as chroma faults or problems with the trick function such as no picture during FF or REW search in LP mode.

John.

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