You may recall back in August I had acquired one of these players, the thread is here. That player powered up but had a missing 12V rail, this was down to a failed STK5481. A new one was ordered and fitted, belts changed, then I got in a bit of a mess with the mode switch. Long story short @jayceebee my mentor in all things came to the rescue, and it was soon correctly set up. However, the machine proved to have a playback fault and despite spending many hours neither John nor I managed to figure out where the fault was, so it was parked.
A little month later, I managed to acquire another exact model, sold as dead, no power. As it was peanuts, I thought it would be a good spares machine for the other one, and importantly it could be used to compare against the other one to aid finding the playback fault on the first machine, so bought it. Since then, I've been distracted with other repairs of TV's and the teletext boxes.
Fresh from success with the Finlandia PSU, and not wanting to start a TV due to an imminent TV arrival at the weekend, I thought I'd get this second FV21R up on the bench and see if I can figure out why this one has a dead PSU.
As @jayceebee pointed out on my Finlandia thread, my bench does seem to attract troublesome projects, examples such as the G6, labgear, 9000 etc are littered throughout the forum.
Glad to see you get something of a normal fault for us bench engineer instead of the horrors that seem to come your way.
Anyway, I wanted to see if this second FV21R would give up the secret as to why it is dead. Upon removing the cover, I noticed blacking to the underside of the lid...hmmmmm. The three fuses were intact. I then set about removing the PSU from the VCR, four screws, two plugs, and it was out, easy to check things out then.
Not a lot to this PSU compared to the Finlandia I worked on over the weekend.
Then my heart sank and as Mork would say, "Awww SHUZBAT!"
I think it looks like the transformer may have died! I'll take some ohms readings on the primary and four secondaries to see how they read. At least I can compare to a know working one.
Another waste of time, I suppose, as the other FV21R PSU is OK, but has the unfathomable playback fault, I could take the PSU out of that and put it in this, then see how this one performs.
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OK, I've mapped the two PSU's transformers, working and non-working. The only discrepancy I can find is on the 1-2 winding, on the primary side. On the cct that winding has a fuse symbol and labelled T.F. See circuit diagram above.
Never come across this before, at a guess is that some sort of internal thermal fuse, hence the T.F.? The outline of that carbuncle on the TX looks very circular.
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Yes it's a thermal fuse buried in the windings and I wouldn't worry about the resistance difference at all at 0.06 ohms. Don't worry about that on the windings either, it's just a blob of the lacquer that was used to seal the windings. The PSU is very simple and should be pretty straightforward as the TX looks OK from here.
John.
OK, cool, I think from this photo, you can see why I thought the TX was not well.
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There's one component I would make a beeline for. I won't make it too easy for you.
I tried to use the spoiler but I could see the component I tried to hide.
John.
I know where you're looking, and indeed R1 the 10R fusible resistor is open. Question is why, I don't like to just replace, but like to understand what may have caused it so will need to study the cct.
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Never had it fail due to any external causes but knowing your luck.
John.
Finding fusible resistors used to be a pain, but earlier this year I managed to find a pot at the end of the rainbow! .5W, 1W and 2W, a new 10R .5W installed and yes, it's back to life.
However, it powers itself off after 5-seconds. I checked the 12V & 5V rails before it goes off, they are both present. This is curious, is this some sort of self-protection shutdown? I checked voltages of CN1 & CN2 supplies out of this VCR PSU against the working VCR PSU that does not shut down.
PIN........Expected......Actual....................... Compared to working machine
CN1 -1 18.1V...........18.6V.......................... 18.3V
CN1 -2 - ................. -............................... -
CN1 -3 - ................. - .............................. -
CN1 -4 18.2V...........17.8V.......................... 17.9V
CN1 -5 19.4V...........19.4V.......................... 19.5V
CN1 -6 8V............... 8.9V........................... 9.2V
CN2 -1 GND............. GND ......................... GND
CN2 -2 -30.4V..........-30.1.......................... -29.8V
CN2 -3 -20.6V..........-20.3V ....................... -20.2V
CN2 -4 -20.6V..........-20.4V ....................... -20.2V
CN2 -5 ? ................ 8V............................. 8.8V
CN2 -6 44.5V............ 45V........................... 46.1V
Nothing up there, must be something else.
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Sounds like the system control is not happy with something. First check that the motor 12V is present, I can’t remember if it’s present all the time or only when the switched rails are up. If it’s there wind the deck loading motor by hand without a tape inserted until the guides are halfway to the heads then apply power and see if they go back to the unload position.
John.
Motor 12V is present on pin 9 of the STK5481.
I managed to get the carriage to go forward and to drop into position, I cannot get the guide posts to move. I have tried to rotate the cogs underneath, they appear seized solid. Applying a little force clockwise shows the post wanting to move a few millimeters but seems locked.
Also spotted the idler tyre has split open, I wonder if something jammed and that's what's causing the shutdown.
Looks like I have another heap of trouble crossing my bench
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You might be lucky and find it’s just the grease gone hard but on rare occasions the wall of the slot of the cam gear that move the guides split. Still leaves the reel idler to source, don’t think I have one of those.
John.
You might be lucky and find it’s just the grease gone hard
Correct, squirted some cleaner, and it's moving now, I set halfway and try your test.
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Sounds like the system control is not happy with something. First check that the motor 12V is present
So it is present
wind the deck loading motor by hand without a tape inserted until the guides are halfway to the heads
I did
apply power and see if they go back to the unload position.
It returned successfully
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That’s good news. Did the tape carriage eject and if it did does the LED on the operate button stay lit now? If not turn your attention to the carriage.
John.
That’s good news. Did the tape carriage eject
No
does the LED on the operate button stay lit now?
No
If not turn your attention to the carriage.
OK 👍
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OK, someone here before me, the plug was out of the carriage motor. Reconnected and now it loads and unloads and stays powered up. Cannot go any further now as the idler tyre is split in half. I will check my stores and be back.
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Part number was PU58645. there were revisions with the last ending -1-4
John.
Found an idler tyre that was pretty much near to the original. Fitted tried RW, that was OK, FF was not good, no movement. Tried again and it jerked a bit then started.
Tried play and that worked OK, picture awful.
Cleaned heads, that sorted that, lovely and clear.
I'm currently running at full backwards, then forwards to see if things free up. At least this one does not have the curious playback fault the other FV21R has. Dare I say another win?
Part number was PU58645.
How the heck do you remember stuff like that, yet forget your breakfast?
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Well done, these were usually very predictable and usually didn't hang around too long on your bench. Fairly easy to work on and access most PCBs until they went to a centre mound deck mounted on top of a single PCB
How the heck do you remember stuff like that, yet forget your breakfast?
I'm a mine of now useless information but can't take in anything new anymore. Need more RAM or just erase the old stuff 🤣
John.
Working very well now, and the remote too.
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