1978 Philips N1702: Another 70's VCR Repair  

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crustytv
(@crustytv)
Vrat Founder Admin
Posted by: Jayceebee

According to Mikey405's old technology website suggests the N1700/1702 differences are a four digit counter, a nine day timer and a test signal generator. I wonder if there is a switch at the rear to activate the test signal as with early VHS machines or knowing Philips could it be active when the CPU  sees no valid video signal or AFC?

In answer to the query as to how the N1702 deploys its test signal. As I mentioned above there isn't a switch at the back but reading Philips CES 66, it states the following:-

" The N1702 is no longer delivered with a colour bar test tape. This is because the machine now has its own tuning signal built-in, which is operated by depressing the start and record keys with the machine switched on, and without a cassette loaded. The signal displayed from the recorder is a pattern of vertical black & white bars."

 

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Posted : 10/02/2019 6:44 pm Red_to_Black liked
Jayceebee
(@jayceebee)
Prominent Member Registered

Good to know, does it work?

John.

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Posted : 10/02/2019 6:55 pm
crustytv
(@crustytv)
Vrat Founder Admin

Some further investigations were carried out today. I removed the additional Video\Audio input\output module from the N1702, desoldering it entirely from the signals board and the channel selector module.

I then tried tuning the VCR's channels to the incoming test signal for E-E, absolutely nothing doing. The only observation I noted was upon powering up the VCR, the tuning indicator light briefly flashes.

I then decided to fit a spare signals board I had from the bare-bones N1700. Once this was installed the tuning indicator light was fully illuminated showing the VCR had recognised a signal was present, this is what you would expect. Selecting a channel on the VCR allowed me to establish E-E.  However this spare signals board has a fault all of its own, in as much as the picture is degraded on both video playback and tuning into the test card signal, well it would be too easy if it was fully working.  🙄 

work

The conclusion to this is either there are further modifications that have been made to the N1702 signals board that I have missed, there is a fault or something else is going on. Tomorrow I'm going to put the original 1702 signals board back in but before I do that, it will go under the microscope for a full close up inspection to see if anything has been added, changed, removed, modified or broken. 

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Posted : 11/02/2019 10:37 pm
crustytv
(@crustytv)
Vrat Founder Admin

Some success, I will do a video later as it would take an age to write up.

Needless to say there would appear to have been two issues with two of the N1702's boards (signals and channel selector module. Well three if you count the corrupt LED clock display, though that is unrelated to the E-E fault. I wonder if that's why the additional video output/input/audio module had been fitted to the machine as a way of getting over a fault.

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Posted : 12/02/2019 12:40 pm
crustytv
(@crustytv)
Vrat Founder Admin

As promised, the video covering the N1702 signals fault, suspects and what likely steps can be taken next. 

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Posted : 12/02/2019 9:30 pm Red_to_Black liked
Jayceebee
(@jayceebee)
Prominent Member Registered

Excellent work Chris as ever and the playback does look good. Am I right in thinking there are no circuits for the electronics inside the cans and servicing was exchange units from Philips?

John.

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Posted : 12/02/2019 10:29 pm Red_to_Black liked
crustytv
(@crustytv)
Vrat Founder Admin
Posted by: Jayceebee

Am I right in thinking there are no circuits for the electronics inside the cans and servicing was exchange units from Philips?

I was wondering about that, the Uxxx are plugin modules in cans, little printed circuit boards that edge connect into sockets in the signals panel. All I had managed to find thus far circuit wise, were the plan views for the signals boards that show where the plugins connect via the edge connectors. There are pointers to these that show expected voltages and wave-forms. I can at least check these to see if anything looks way out.

However, I've also now discovered more intrigue on the 1702 signals board. As I explained in the video above, the N1702 board differs from the N1700 in the reference processor module is U533 and has this built in test pattern former. Whilst the N1700's reference processor does not and is designated  U513.

Well my N1702 board has a U513 module fitted, not the expected U533. This now fully explains why I'm not getting the test pattern generated, the wrong module is fitted! This further reinforces that someone has been in here for either good reason of bodgery, which it is, as yet I have no idea. Its difficult enough when you're learning VCR repair without having to deal with 40+ years of other peoples agile minds either doing good or bad mods/repairs.

I'm now left with two questions and another night of dream diagnostics. Is the U513 1700 module compatible in the U533 position of the N1702 signals panel. If its not then I'm stuffed. Is the only difference the test pattern gen. If U513 is compatible in a 1702 signals board then I might have a fighting chance through diagnostics and substitution.

All fun and games and I'm enjoying the ride I hope members are too.

u5xx 1
u5xx 2
u5xx 3

  

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Posted : 12/02/2019 11:01 pm
Red_to_Black
(@red_to_black)
Noble Member Registered

Just to stop you p****ing in the wind here, I have some other info. I will try and post it tomorrow evening. Suffice to say the panels U513 and U533 are not interchangeable.  

 

"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 : 12/02/2019 11:44 pm
crustytv
(@crustytv)
Vrat Founder Admin

Posted by: Red_to_Black

Just to stop you p****ing in the wind here [..]

Hi Baz, 

A rather colourful expression! I think that's the first time its been suggested my potential investigations and actions might be described as "p***ing into the wind". I'll admit navigating the occasional blind alley but they all offered great value, you don't learn from successes you do learn far more from mistakes. 

All my threads, for all these years, report my findings as they happen, as I investigate them. This in preference to how others work where some folk do " Ta-Daaaaa - its all done folks and here's a brief synopsis of what was done", type threads. Don't get me wrong, each to their own, no criticism intended to those that take that approach as those type of threads are very interesting too. The down side to my approach is I have often and frequently attracted flak.

As I said above in my last post yesterday evening, and the comment was just rhetorical:-

Posted by: Crustytv

I'm now left with two questions [...]  Is the U513 1700 module compatible in the U533 position of the N1702 signals panel. 

It was getting late, I had spent the best part of an afternoon and evening producing, editing and uploading the video of that days work. I thought I would leave the next phase, the U513/U533 question, until the next day. I therefore just expressed what was on my mind at that point in time. As I clearly indicated in my video investigations, I was already highly suspicious that the problem was lying in the reference processor and that was where I would be next focusing my efforts and attention.

I had hoped the threads and youtube videos where showing my methodical approach to problem solving on the Philips N1500 and N1700 series VCR's. That despite not having ever worked on VCR's before, my approach and determination, had not only allowed me to identify the fault with the N1500 and rectify it. That I was also well on my way to identifying and solving the various faults encountered with the two N1700's and in particular the curious additional module and lack of E-E with the 1702 signals board.

As detailed at the outset of the thread and opening video, thankfully I have the full manual. As planned for today, I checked the modifications section, in particular looking for listed differences between the 1700/02, it did not disappoint as shown below. Clearly as you also already knew the U513 is not compatible, well that's not entirely accurate. Further investigation revealed this is permissible but as a pair U512 & U513 can be used but for it to work you need to remove D516 and D517 and finally R526. 

manpage

My 1702 signals board and it is a 1702 signals board, has a U512 fitted and D516/D517 are removed but..  ** It would seem R526 has not been removed ** (see attached below). Further investigation also shows six of the modules are N1700 and not N1702 modules. (see map below). It just gets better doesn't it.

r526

 

N1702 Signals board: Red shows discrepancies

 

Module function What should be present on the N1702 board Actually fitted
SOUND U539 U539
REF PROC U533 U513
562KHz U532 U512
CHR OSC U535 U515
CHR AGC U534 U514
SIG PREP U531 U511
AGC U537 U507
AMP U505 U505
F-DET U506 U506
SOUND FAFA U508 U508

 

The investigation fog and mystery of this N1702 and its additional video module, is clearly starting to lift and reveal itself. As to why they also fitted the "Signal Splitter" module via CH8  I guess we'll never really know what on earth their reasons behind all this were. To be honest I'm not going to try and unravel this mess!

My plan of action now is simple. I have the N1702 machine working albeit its really a N1700 now, I just need to test recording, adjust the friction drive and its finished. The first N1700 which is now missing its signals board will get the bare bones signals board that has the chroma fault, I will diagnose and fix that. This will give me two working machines. The N1702 franken-hybrid signals board will be put into stores and used as spares, after all over 60% of its modules are N1700.

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Posted : 13/02/2019 7:54 am Red_to_Black liked
sideband
(@sideband)
Famed Member Moderator
Posted by: Jayceebee

Am I right in thinking there are no circuits for the electronics inside the cans and servicing was exchange units from Philips?

They weren't even exchange units. The idea was that these modules were treated as spare parts and just replaced when faulty. We were not expected to fault-find the modules (mainly because some of them would have been almost impossible to work on when in situ). Sometimes circuits of the modules were shown, generally in the 'Circuit Description' (which was usually a separate addition to the service manual). The only time we dived into the modules was if any were out of stock or unavailable for some reason. A few of us were quite happy to open them up and change IC's or transistors as required. 

 

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Posted : 13/02/2019 10:36 am
Jayceebee
(@jayceebee)
Prominent Member Registered

Is there also any way to confirm that the pcb inside the can matches what's printed on the label. Hopefully the U type number may be etched onto the print side of the board?

John.

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Posted : 13/02/2019 12:10 pm
crustytv
(@crustytv)
Vrat Founder Admin

Hi John,

The PCB's in the modules do not have the 'Uxxx' designation stamped anywhere on their boards. There are some codes on the print side but these do not tie in with the U513 or U533 part codes as listed in the service manual, which is what I would have expected them to be.

I can however confirm the PCB in the U513 that came from the N1702 signals board matches identically with the other two U513 modules from the other two N1700 signals boards. All three are identical, I would say its a safe bet they are U513.

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Posted : 13/02/2019 4:33 pm
crustytv
(@crustytv)
Vrat Founder Admin

This morning for a little light relief from the technical and brain-hurt that other signals panel has inflicted, I decided to give the chassis its long needed dust down and degrease, then re-lubricate. It looks and operates now much better for it. Its actually in remarkable condition and along with the N1500, a fine example of the type of early VCR available at the start of the home recorder boom.

cln 1
cln 2

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Posted : 14/02/2019 12:22 pm
Red_to_Black
(@red_to_black)
Noble Member Registered

Hi Chris,

First off I did not mean to imply any of your investigations were peeing in the wind, far from it, I thoroughly enjoy your write ups and latterly your videos immensely, you are very brave imo.

I had just come across that same page you have since posted up detailing the mods in production, and which I had indeed intended to post it up last night (work in the way), it was intended to save you from potentially mixing incompatible panels/modules muddying the waters even further.

I was not at the time sure if you had seen that page or were even aware of it and I was going to hi-light the same bits you yourself remarked upon, it was getting late and I was tired and as I say I had intended to post it up for you last night if you had not already seen it, it was more intended to help save you getting muddled up rather than anything else.

Carry on the good work 🙂

"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 : 14/02/2019 8:47 pm
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