Hi everyone,
my name is Gunther and I'm from Germany. I've had an N1500 since I was a kid, it was given to my by a friend from school in the late 80s/early 90s. With the help of my dad, I got it running. Back then, it was only mechanical issues that prevented it from working. As I had no idea what I had on my hands back then, and as I was a curious kid, I played around with the VCR a lot, put stickers on it, etc. After some years, I lost interest in it, and it disappeared in the basement. During the Covid lockdown, I remembered the VCR and made the plan to bring it back to life.
First, I had to deal with mechanical issues again, replace the belts, fix the pinch roller, but also with some electrical issues. Several capacitors had gone bad (especially the low capacity electrolytics). After replacing them and improvising a stand to be able to make the necessary servo adjustments, it was working surprisingly well. I decided to clean it thoroughly before putting it all back together, and that's when it happened. I broke one of the video heads... Hard to believe that I managed to do now what I had not managed to do in all those years messing with the VCR. While I was able to glue the head back in place, the position doesn't seem to be perfect, so the image is much worse than before.
As I really wanted to have a well working machine, I went on the hunt for a replacement head drum or a parts machine. After a little while, I found a parts machine for a reasonable price. After picking up the machine, I was surprised at its good overall condition. It seemed to be complete, all the disintegrated belts still in place. After cleaning everything out and replacing the belts with new ones, the VCR was working from a mechanical perspective. Having replaced the critical electrolytics, I managed to play back a tape and receive the signal from a test pattern generator. Unfortunately, both were of very low quality. While the playback image was free from stripes, it was initially without color and of very low contrast. The EE signal had color, but was unstable and noisy. After cleaning some contacts, fixing a cold solder joint and replacing a missing connection. The EE signal is now stable and in color, but still pretty noisy. The playback picture is not noisy, has a bit of color now, but is still low contrast/inverted.
As the playback picture is not noisy, I assume the modulator is working fine. Also, the heads seem to be ok, as there are no dropouts and the picture is clear. However, I don't know how to proceed in order to improve the picture. I am still waiting for a new pinch roller, as the one I have is pretty bad. I hope this should fix the periodic jumping of the image.
The EE image issue seems almost harder to fix. The automatic gain control seems to be working fine, reducing the output of the test pattern generator only leads to a noisier picture after the output has been reduced quite a bit.
Unfortunately, I only have the complete manual in Dutch, the very helpful troubleshooting section is missing in my German version. Could anyone maybe help out with a digital copy of the English version?
Also, if any of you have any pointers, please let me know what to check! I am fairly experienced with electronics (electrical engineer) and have quite a bit of test equipment, but the N1500 makes it really difficult to proceed systematically, as everything is so hard to access.
Thanks in advance,
Gunther
Hi Gunther, welcome to VRAT.
I've just copied the Full English version of the N1500 service manual into the temporary download area of our data library. I've just fast tracked your membership to include access to this data area. I don't normally do this as we've had no end of new members turn up just after something free, never staying around to be part of the community and share their repairs with us.
It's a large file almost 1GB. Please let me know when you have downloaded it so I can remove it.
Good luck with your repairs, I have three of these machines, all in various states of repair, one nearing completion. Indeed the diagnostic section of the manual is a must have aid to assist with repairs. Parts are getting harder and harder to find and like you I've bought a number of parts machines.
Thank you so much for your kindness! I will download the manual tomorrow once I‘m back on my laptop. I‘d be happy to share whatever insights and pictures I have about the VCR!
I’m really surprised that my first machine was working so much better than this one, but the second one is just in way too good a shape to be used for parts only…
Well, two steps forward, one step back... With the full manual, I started on the troubleshooting section. As my VCR did not turn off after being turned on an no tape transport button being pressed, I checked that area of the device. I found that a trace on a PCB was interrupted, even though not visibly. After fixing the connection, the VCR now turns off almost immediately. The manual points to TS112 in this case, which I don't believe is faulty. The tape transport buttons are released as they should be when the device is turned off.
I suspect that C115 is being charged too fast, will have to check capacity and the resistors in that area.
This thing is really full of surprises!
Well, two steps forward, one step back...
That's the sort of progress I so often encounter, deeply frustrating, and Philips certainly don't make things easy.
That protection circuit is fun filled for sure, I spent some time diagnosing a fault with one of mine. If you've not read it, here's a link to the thread.
@crustytv I actually had read your article before! It's funny how seemingly fairly simple circuits like the protection mechanisms can be so difficult to diagnose. I've also read some of your work on color TVs, absolutely amazing! Being from Germany, I'm not very familiar with Thorns and Pyes however. I just found and fixed an old Grundig 1510 where the core of the 5.5MHz trap had broken off almost invisibly...
Maybe I should have stuck with my original plan of using this machine for the good head drum only, but it was just in way too good a shape to pick it apart. I even found an original lacing drum and cord, the machine has the potential to be almost as good as new...
Well, not a whole lot of progress, but I still want to update this thread. The new pinch roller did not fix the unstable picture issue. However, it really seems like a mechanical issue. Synchronization works just fine when adjusting it for recording, without a cassette in the VCR. Maybe there is too much friction somewhere... However, in the time when the picture is stable, it is pretty decent, however the colors are a bit weak and there are lines across the screen sometimes. It doesn't seem to be a head issue, as this phenomenon depends on the image content, the signal seems to be overdriven.
Will try to fix the tape speed issue and see what happens. Still need to deal with the faulty protection circuit and the EE-singal issues..
After a long break, I'm back at working on the N1500. Some progress, but still a long way to go.
The issue with the synchronization has been fixed, but I'm almost embarrassed to say what the issue was. With the location of the pots, the VCR up on a jig to get access to the underside of the PCB, combined with all the wires on top of the PCB, I was adjusting the wrong pot 😖. After finally realizing this, playback now synchronizes ok.
The issue with the VCR turning off immediately was also sorted out, it ended up being another bad trace on the PCB.
This leaves the issue with the bad EE picture. I realized that the PFAT was not being deactivated properly during tuning due to bad contacts. After shorting the contacts, tuning works ok, and following a simple readjustment of the PFAT circuit, it no longer interferes with the tuning. Still, the image is very grainy. As diagnosing a fault in the HF circuits, I suspect issues in the IF amp, seems rather difficult, I wanted to hear your thoughts about replacing the lockfit transistors in that area. If read elsewhere in this forum that they are frequently a cause of concern, so I was wondering whether this might be the way to go. Would love to hear your thoughts!
Thanks,
Gunther
Snow is usually a front-end issue. Try putting a battery box / pot on the tuner AGC, see if adjusting it clears the snow.
If it makes no difference, suspect RF amp transistor.
If you can clear up the snow, it's an AGC issue.
Thanks a lot for your insight! I will definitely try the battery. I hope the rest of the issues with playback won't be too hard to figure out.
I did some checks, the AGC seems to be working fine. I guess that leaves the RF amp. As the issue is present in both VHF and UHF, I assume that the RF amp inside the VHF tuner is what I should look at? Thanks to @crusty, I have the full manual, but there seems to be no detailed circuit for the tuner part. Does anyone know what type of transistors are inside?
Again, thanks a lot, without you guys I would have given up a long time ago!
You will probably find a BF200 in there. Has to be replaced with that part. They were known for going open circuit B-E.
Thanks for the response, I opened up the tuner and really did find a BF200. Will order a replacement and hope that this clears up the noisy picture issue.
Thanks to @crusty, I have the full manual, but there seems to be no detailed circuit for the tuner part. Does anyone know what type of transistors are inside?
That is because Philips regarded the tuners as a 'black box' and therefore a replacement item only. We all used to pull them apart and fix them though. Check any earthing connections as well.
That’s exactly why I‘m so happy to have found this forum! Without all your support, I wouldn’t have known where to begin.
Meanwhile, I have pulled out the transistor, it only shows up as a diode on my tester. We will know more when the replacement arrives.
Well, the transistor arrived and I replaced it, but unfortunately it didn't yield the desired results. If anything, the picture is worse that it was before. I also noticed that the image quality varies when I move the front end PCBs around. I have found some bad connections and also bad tracks on the PCBs in that area before, they don't seem to be of the highest quality. As it's very difficult for me to diagnose something that I don't even have the circuit diagram for and that, due to the high frequencies in that area, is difficult to measure, I am very tempted to replace the front end with the one from the other N1500 I have. I don't want to give up, but this project is a bit frustrating...
I presume you checked the new transistor before replacing it? If the old one only showed up as a diode on the tester then a replacement should have made SOME improvement.....
To be honest, I didn't. I bought a pack of 5 transistors, so I can check how the others show up on my tester. I was in a bit of a rush, just wanted to get the part in and see the improvement. My suspicion is that there is one (or several) bad connections that are the main cause of this issue...
I'm seriously thinking about testing the VCR with the front end from my other N1500. If that works, I'll see what I can do about this one.
Well, I‘m an idiot! I took the tuner back out to take it apart and found that I must have bent one of its pins during installation. I rectified this and I‘m back to the VCR working as well as, or maybe a little better than, it was before the transistor replacement. It seems like VHF tuning is working better than before, I couldn’t really get it to tune into a signal on that band before. Still, the image is a bit grainy. Sound is fine and color seems to be ok too. Should I start looking at the luminance amplifier around the delay line, after the IF stage?
