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JVC HRD-750 VCR - early NICAM

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Refugee » Sun Apr 20, 2014 12:54 pm

I would pick one form this selection. They can be restocked from the usual suppliers in a full range.
The leads are long enough for them to be used in a radial form position with a little bit of sleeve added if that are in a crowded board.
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Re: JVC HRD-750 VCR - early NICAM

Post by Alastair » Sun Apr 20, 2014 5:37 pm

Aidan--

If you like how well made your current JVC project is, Take a look at the semi-professional S-VHS JVC BRS800 and BRS822 recording/editing decks They are often accompanied by the BRS600/622 playback only machines with a matching deck controller unit....

They turn up cheap now from time to time on the usual sources, and are outstanding in both build and picture-quality--even blown up to 50" :aad

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Mon Apr 21, 2014 3:37 pm

Have ordered the N-types, the machine had the F-types.

I was thinking if the voltages turn out to be OK but the machine still has the fault, would it be random hash on the rails? For obvious reasons a multimeter wouldn't be able to pick up on this, if present.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Mon Apr 21, 2014 4:04 pm

AidanLunn wrote:Have ordered the N-types, the machine had the F-types.

I was thinking if the voltages turn out to be OK but the machine still has the fault, would it be random hash on the rails? For obvious reasons a multimeter wouldn't be able to pick up on this, if present.


Aidan once you have the regulator working correctly I will add more information, at the moment I have held back on other stuff to save more confusion.

I feel it would be rather counterproductive to add this at the moment.

The secret of repairing things is to start with the fundamentals and follow a logical course, bouncing backwards and forwards before getting the supplies correct will just muddle things up and may either introduce other faults and/or end up replacing stuff that is not faulty.

There is little point going any further at the present time, as we would be just stabbing in the dark with not being able to prove anything.
If we can get the machine back to a known condition I don't mind helping further if I can.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Fri May 02, 2014 2:47 pm

I have replaced the N-20 and N-38, these appear to work fine, now I've discovered N-16 is o/c.

Would an N-15 or N-20 be suitable as N-16s seem rare, doing a Google search for "ICP-N16" yields nothing useful.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Fri May 02, 2014 2:54 pm

what is the circuit location ? ie. Cp number, as far as I am aware ICP-N16 doesn't exist, as this works out @ 640 mA which is a non-standard value.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Fri May 02, 2014 3:00 pm

Can't remember the CP number but it's right next to the other two that I've replaced, one of the three going from the PSU block on the input to the regulator.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Fri May 02, 2014 3:07 pm

Okay,
They are
Cp802 = ICP F/N 25
Cp803 = ICP F/N 38
CP804 = ICP F/N 25

F/N - F or N type

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Fri May 02, 2014 3:19 pm

Red to black wrote:Okay,
They are
Cp802 = ICP F/N 25
Cp803 = ICP F/N 38
CP804 = ICP F/N 25

F/N - F or N type


Ooops, I've mis-read it. The one in question was pretty hard to see. With the tiny print they used on these, a "16" could have looked like a "25".

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Fri May 02, 2014 5:09 pm

Have replaced the CPs. Now I'm back where I started. Taken measurements again, this time the AC pins on CN2 measured 19V across them, instead of 3.9V. Pins 2 and 6 were -35V and 50V respectively.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Fri May 02, 2014 5:15 pm

Aidan forget about the AC voltage for the moment, please give me the DC voltages after the regulator.

If the regulator voltages are not present and correct then we will never get it to work properly, other supplies are dependent on the regulated supply.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Fri May 02, 2014 6:58 pm

All the voltages on the output of the regulator measure OK, within 2V of the published values. They measured OK before I blew the CPs.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Fri May 02, 2014 7:24 pm

Okay, the switch/display board requires a number of supplies to function.

They are the AC 3.9V supply for the heaters of the VFD (the display itself).
An un-switched 5V line, this is derived from the un-switched 12V line via Q1 on the Timer panel.
The -30V line (this is for the IC that drives the VFD) for the VFD.
A switched 5V line
And an unregulated 7V line.

There is also an un-switched 12V rail which is routed through the panel to the operation PCB, this does not appear to be used on this panel itself.

I will try to scan the power distribution diagram showing the points these can be measured shortly.
The diagram is difficult to scan.

We first need to establish what you have and have not got present, you may well find once you locate a missing supply line that it will be the reason for multiple symptoms.

The AC supply is only for the heaters of the fluorescent display itself, if this was missing the machine would work normally in all other respects apart from no fluorescent display.
I suspect that one of the other key voltages is missing, giving you the symptoms you have.

Some of these supply lines you should be able to trace point to point with cold continuity tests, others you will have to check with the machine powered up, so try not to short anything out.

The other point is my manual covers the Ferguson FV33H so the physical layout may be slightly different, the circuit itself though should be near enough to find your way around.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Fri May 02, 2014 7:46 pm

OK,
Here is a Scan of the relevant part of the power distribution diagram, this has the main parts of interest to us for the moment, at the bottom switch/display board 28. I can scan smaller parts in more detail if required.
This gives an overview of the main bits we need for now, when/if you find what is missing we can look at the circuit diagram at the relevant components in more detail.

I have saved this as a Png file so you can save it to zoom in.
If you have difficulty viewing via the forum I will e-mail it to you as a Pdf.

Edit: the unregulated 7V supply is common to part of the audio you were having problems with.
Attachments
FV33H PD 01 001.png

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Fri May 02, 2014 10:19 pm

Well I haven't made any more progress on this tonight, but to recap, I have measured all the output voltages on the main PSU and the regulator - ignoring the AC lines, all measured within 5V of the values printed in the FV33H service manual.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Sat May 03, 2014 11:26 am

AidanLunn wrote:ignoring the AC lines, all measured within 5V of the values printed in the FV33H service manual.


I hope that is a Typo Aidan, dmm any regulated (after the regulator) supply lines need to be a lot closer than that.

I don't know if I posted this before, but if not perhaps I should have.
The PSU on this model is checked and set by measuring CN-1 pin 1 to ground with a digital multimeter it should measure 15.3V, the machine should be powered on.

You set the voltage by adjusting R9 (which is the pot on the PSU).

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Sat May 03, 2014 2:50 pm

Most of them were within 2V. The 45V and - 30V rails were both 5V out, so altogether, all of the outputs on CN2 and the regulator stage were no more than 5V out. IIRC, the unreg 7V rail was about 7.2V

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Sat May 03, 2014 2:58 pm

The un-regulated ones, particularly the higher ones will vary a bit.

The important one is the one used to set the PSU, with the machine switched on @ 15.3 V at Test Point CN-1 pin 1 to ground, assuming the machine can be turned on. If this supply is not fully loaded due abnormal conditions it may well be slightly higher.

The regulated ones, post-regulator should be close to their specified voltage, within say 10% of the value of that rail.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Sun May 04, 2014 7:44 pm

Red to black wrote:The un-regulated ones, particularly the higher ones will vary a bit.

The important one is the one used to set the PSU, with the machine switched on @ 15.3 V at Test Point CN-1 pin 1 to ground, assuming the machine can be turned on. If this supply is not fully loaded due abnormal conditions it may well be slightly higher.

The regulated ones, post-regulator should be close to their specified voltage, within say 10% of the value of that rail.


Thanks Baz.

CN1 pin 1 seems to be erratic. I measured it once, correctly, and it was measured at 33V. After half an hour of being unplugged, I measured it again, and it turned out at 17.2V. It seems to be steady after that.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Sun May 04, 2014 10:11 pm

CN1 pin 1 seems to be erratic. I measured it once, correctly, and it was measured at 33V. After half an hour of being unplugged, I measured it again, and it turned out at 17.2V. It seems to be steady after that.


That is quite a variation Aidan, although the output of the chopper transformer is classed (named in the manual) as unregulated it is still actually regulated via the primary side of the SMPSU, albeit maybe not as tightly as the secondary regulated supplies via the fixed regulator on the secondary side.

I would not expect to see such large variations, first off are you sure your multimeter is okay ?
If you are sure your multimeter is definitely okay then you might have a problem in either the STR 1006 chopper IC itself or a problem in the feedback loop.
I will have a closer look at the circuit later on.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Sun May 04, 2014 10:33 pm

Red to black wrote:
CN1 pin 1 seems to be erratic. I measured it once, correctly, and it was measured at 33V. After half an hour of being unplugged, I measured it again, and it turned out at 17.2V. It seems to be steady after that.


That is quite a variation Aidan, although the output of the chopper transformer is classed (named in the manual) as unregulated it is still actually regulated via the primary side of the SMPSU, albeit maybe not as tightly as the secondary regulated supplies via the fixed regulator on the secondary side.

I would not expect to see such large variations, first off are you sure your multimeter is okay ?
If you are sure your multimeter is definitely okay then you might have a problem in either the STR 1006 chopper IC itself or a problem in the feedback loop.
I will have a closer look at the circuit later on.


It's mainly the Ferguson/Thorn manual I'm working off, the one with the added red printed voltages on the schematic, will have been supplied in the full service manual. I usually find the JVC-issue ones to be most unhelpful.

I will test it with another meter tomorrow. For the record, my meter is a Uni-t UT58C.

http://www.uni-trend.com/UT58C.html

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Sun May 04, 2014 10:48 pm

With respect Aidan we are going round and round in ever decreasing circles, you really need to get a grip and sit down and concentrate with fault finding on this machine if you want it fixing, at the moment I have lost track of where we are (and the will to live :bbd ).

I need to know what Voltages we have got, and have not got present, I need you to help me to help you if you catch my drift, I need feedback and answers to make any headway.

Fault finding is difficult enough via a forum, now I know you are a novice but I really need consistent answers to help you, can't you get some help locally ? from someone with more experience ? I can still provide technical help but we really need to make some progress.

ttt:

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Refugee » Mon May 05, 2014 4:35 am

Can we get a scope on the AC side of the diode that feeds the 15.3 volt rail?
I would not be pointing my finger at the STR chip just yet.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by AidanLunn » Mon May 05, 2014 4:39 pm

Well I blew two of the fuses trying to measure the input of the regulator again when trying to measure here so I went and ordered 15 N-25s and 15 N-38s, so it would be futile to measure anything here until these CP fuses are replaced.

It's beginning to frustrate me, too. there aren't that many places near me that do VCR repair anymore, and those that do want a £50 assessment fee from me first, even if I explain that I'm in this hobby.

Refugee, I do have a scope, but have no idea how to use it.

 
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Re: JVC HRD-750 VCR - early NICAM

Post by Red_to_Black » Mon May 05, 2014 5:04 pm

Okay when you get your replacement CPs we will start again from the beginning.
We need to get the PSU DC voltages measured correctly, I cannot stress how important this is, the supply rails need to be in the correct ball park and stable before anything else, if we don't get this correct we are just wasting our time.

I don't mind guiding you but I will need to know what the actual measurements are, and exactly what has been done parts replaced etc. I will ask this from time to time as this determines whether we step forwards or backwards, and check your meter please, I know some voltages may vary slightly from the published but a 2:1 step change is a bit far out, the various voltages that are output from the chopper transformer tend to track each other.

This particular PSU is mostly reliable, there are rarely any major problems, we need to step through the measurements in a logical sequence and methodically, if there is something unclear or that you are unsure about then please ask, guessing games and assumptions are of no use to anyone.

Edit: Actually Aidan there should really be no need to keep blowing the CPs, as most of the supplies can be measured at a connector or at a test point, or even at an easily accessible component leg, you just need to be careful.

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