UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Reply
 
Thread Tools
Old 13th Feb 2024, 6:56 pm   #1
Malcolm G6ANZ
Octode
 
Malcolm G6ANZ's Avatar
 
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,048
Default PM 5519 pattern generator

I powered up this pattern generator and was rewarded with no out put and a slight hot resistor smell. The smell was coming from the current limiting resistor in the psu. I checked the smoothing capacitor after it and all was OK. Disconnecting the -12v from the main board brought back the-12v on the PSU so the caps and the 7912 were OK. On the main board the -12V line is split into 5 rails each with its own series resistor and smoothing capacitor. The resistor feeding the -12V E line was also cooked. Resistance measurement here showed a direct short to 0v (0.6ohm)I checked the associated smoothing cap by cutting it out of circuit. there was still a short to 0v.
The switch at the bottom of the diagram is OK.
From the diagram the -12vE only drives the video output stages and a relay for video in. I can't figure out how there is a short to 0v. With the -12vE disconnected by opening the jumper ,as shown by two black dots on the diagram, almost normal working was restored. in as much as there is a video output although small and inverted, not unexpected.
Ideas anyone?
Malcolm
Attached Thumbnails
Click image for larger version

Name:	Main board power distribution.JPG
Views:	120
Size:	94.4 KB
ID:	292884   Click image for larger version

Name:	Power supply.JPG
Views:	119
Size:	109.8 KB
ID:	292885   Click image for larger version

Name:	Video output stages.JPG
Views:	115
Size:	122.6 KB
ID:	292886  
Malcolm G6ANZ is offline   Reply With Quote
Old 13th Feb 2024, 8:35 pm   #2
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Hello Malcolm.

I agree, looking at the circuit diagram, it's difficult see how a short circuit from the -12E rail to ground can occur. Each feed point is connecting to a moderately high (compared to the 0.6 Ohm short) value resistor.

Just wondering, do you know the history of your pattern generator and has it been working recently?
It's possible there may be a solder bridge on or beneath the main board. I'd first give the main board a good visual check on both sides.
Maybe a milli Ohmeter from 0V to each -12E feedpoint in the video stages will narrow down the approximate location of the short.

I have a PM5519 in my collection but haven't yet tested it. Once I've located it, I'll have a look inside and assess the circuit in relation to the circuit diagram. It will be a day or two before I can open it for tests.

Regards,
Symon

EDIT: I assume R760 is the one that's overheating?
Philips210 is offline   Reply With Quote
Old 13th Feb 2024, 9:16 pm   #3
Malcolm G6ANZ
Octode
 
Malcolm G6ANZ's Avatar
 
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,048
Default Re: PM 5519 pattern generator

Symon, thanks for replying. You're right it is R760 overheating.
History: it's been working correctly ever since I 'liberated' it from work several years ago. To my knowledge the cover has never been off until now.
One other thing that I noticed, the 75 ohm series resistor R 744 in the video output has also overheated, although this may be a red herring and was caused a long time ago. I've checked the series coupling cap and its OK.

Malcolm
Malcolm G6ANZ is offline   Reply With Quote
Old 13th Feb 2024, 9:43 pm   #4
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Malcolm,

That's good to know it has been working fairly recently.

In view of the short across the 12E rail, one would think it's either a small electrolytic cap or a semiconductor junction that's gone s/c. There may be an electrolytic across that rail but isn't apparent on the circuit diagram.

It almost seems illogical to suggest a resistor going s/c and then there'd also need to be say a s/c transistor junction as well to give that low 0.6 Ohm reading. That would probably be an impossible scenario. There could still be a physical short across the rail say a solder bridge, rogue screw, nut, washer etc that's inconveniently lodged itself there.

R744 is probably unrelated but strange all the same. It's as if C543 has been leaky but has now reformed itself.

I'll try to work out the circuit arrangement when I get to see the inside of my unit in the coming days.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 9:07 am   #5
frsimen
Heptode
 
Join Date: Jan 2011
Location: Croydon, London, UK.
Posts: 816
Default Re: PM 5519 pattern generator

Hello Malcolm,

If that is the whole circuit that is connected via R760, all the transistors are connected via resistors to the negative supply. There could be a short across a resistor, I suppose, easily proven by a resistance check, but it's more likely that the problem will be a shorting wire/solder splash between the -12V and a 0V point. Have a look around the Video amplitude pot and the nearby switch, as they both connect to the -12V line without any intervening resistor. A stray wire there, or a faulty pot/switch could be the culprit.

Paula
frsimen is offline   Reply With Quote
Old 14th Feb 2024, 12:13 pm   #6
Malcolm G6ANZ
Octode
 
Malcolm G6ANZ's Avatar
 
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,048
Default Re: PM 5519 pattern generator

Further investigation of the circuit shows that the -12vE goes to another place. The external video input amplifier and the switching relay. The relay coil ends up on a switch by the master oscillator in the diagram. So the master oscillator is switched off when external video is selected and relay 891 is energised to switch the external video in. The relay and switch both appear to be OK with no obvious shorts to 0v

Malcolm
Attached Thumbnails
Click image for larger version

Name:	Video input amp.JPG
Views:	55
Size:	101.5 KB
ID:	292923   Click image for larger version

Name:	Video input part.JPG
Views:	45
Size:	92.5 KB
ID:	292924  
Malcolm G6ANZ is offline   Reply With Quote
Old 14th Feb 2024, 1:19 pm   #7
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Malcolm,

I've located my PM5519 and have had an initial look inside. I am working with a poor quality service manual which is challenging. Also there are minimal component reference numbers on the main PCB adding to the difficulty. Hopefully I'l be able to make some progress with it later today when I am less busy.

I have located the -12 feed from the power supply (the blue wire from the connector) to the main board and have traced a few of the resistors connected to the -12E branch off from the -12 feed. A resistance check from -12E rail and ground is giving a reading of about 500 Ohms.
I'll try to get back to it later.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 3:52 pm   #8
Chris55000
Nonode
 
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,980
Default Re: PM 5519 pattern generator

. . .Some other places that might be worth checking for a short–circuit are :–

. . .Trapped wires that have got nicked, one of which is shorting the –12E line to earth, disconnect the lead to Pin 11 of the main PCB (use "Dazzlevision's" scanned PCB layouts elsewhere on the Forum to help find it) – this leads off to the video amplitude & video on/off switch on the front panel and if the short clears when you disconnect pin 11 the fault can only be in the wiring to the front panel or within the control itself!

. . .The MC1496 multiplier ICs IC318 and IC328 are directly fed from the –12 supply – there might be a short–circuit here that is misleading you because R760 has been damaged and gone low resistance, but if you've isolated the solder bridge connecting R760 to the main supply and still reading the -12E line as a s/c that would rule that out!

. . .(The –12A to –12E supplies can all be isolated by means of the solder–links provided!)

Chris Williams

PS!

Just realised Paula beat me to this one – my apologies, however I am in full agreement with Malcolm and Paula, there is no obvious direct path for the –12E line to go down to earth anywhere on the main board, unless C590 is shorting when power is applied! – a short within relay 891 wouldn't do it as its contact is connected to the positive supply and various video circuit resistors!

. . .Is Relay 891 metal or plastic–cased? – I don't have a '5519 of my own to refer to!
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

Last edited by Chris55000; 14th Feb 2024 at 4:05 pm.
Chris55000 is offline   Reply With Quote
Old 14th Feb 2024, 5:00 pm   #9
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

I've just had another look at my PM5519 and managed to locate all the connections to the -12E rail as they appear on the circuit diagram. So far, I haven't found any other connections to the -12E rail.

Something that has occured to me. There are a some places on the main board where a few of the blue electrolytics cross over the -12E rail. It's possible the blue plastic insulation may have been damaged and the case of the electrolytic is shorting the -12E rail to 0V. I'd check that the insulation around the cases of C531, C533 and C534 is not damaged.

The yellow wire going to the Video level pot could be unsoldered to rule out a short within the pot.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 5:32 pm   #10
Malcolm G6ANZ
Octode
 
Malcolm G6ANZ's Avatar
 
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,048
Default Re: PM 5519 pattern generator

The relay is a reed switch inside a coil. As are all the relays. I’ve cut c590out of circuit.
Malcolm G6ANZ is offline   Reply With Quote
Old 14th Feb 2024, 6:39 pm   #11
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Re post #9. I should have said unsolder the yellow wire to the switched video level pot. That wire connects to the switch rather than the pot itself but Malcolm has already ruled that out.

If no luck finding the short then I'd be inclined to try a milli Ohmeter with 4 leads (Kelvin type) and probe around each -12E feed to close in on where the short is.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 7:20 pm   #12
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Malcolm, later ths evening I'll take another look at my unit to see if I've missed anything ie any other connection to the -12E rail. I'll also try and get some pics of the board.

I guess if the worst come to the worst then you could cut the tracks in parts of the -12E rail to narrow it down but I'd continue looking for any physical signs first. It shouldn't be too hard to find as it seems it's confined to a smallish area of the main PCB.

Were the plastic sleeves of C531, C533 and C534 in order?

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 7:42 pm   #13
Malcolm G6ANZ
Octode
 
Malcolm G6ANZ's Avatar
 
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,048
Default Re: PM 5519 pattern generator

They appeared to be. I’ll cut each one out in turn and inspect them.
I’m starting to think the only way forward now is to feed in a -12v from an external supply and see where the smoke comes from?. A bit drastic.
The board and switches all look in good condition with no visible areas of stress.
Thanks to all for your helpful suggestions. It will be fixed (somehow)
Malcolm G6ANZ is offline   Reply With Quote
Old 14th Feb 2024, 7:59 pm   #14
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

One other possibility. On a similar vein to the sleeve on the electros, one of those feed resistors from the -12E rail may have damage around the end cap if it's situated above a ground rail.
I'll take a close look at the layout of that part of the circuit on my board to see if that's a possibility.

It's an interesting challenge!

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 10:03 pm   #15
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Hello again,

Having had a good look on the main board, I doubt that there will be any problems with the insulation to any of the resistors. I couldn't see any ground tracks running close to them so that possibility now seems unlikely.

I've taken a few pics of the main board concentrating around the video stages and -12E supply rail. Resistors fed from the -12E rail are marked with an asterisk. Something else I noticed re the blue electros. The sleeve certainly is defective on many of the caps. There's a spiral cut in some of them exposing the aluminium case. Notice in particular C533 which is adjacent to R721, R720 and R707 right where the -12E feeds those resistors. Might be worth concentrating around there.

Regards,
Symon
Attached Thumbnails
Click image for larger version

Name:	IMGP9636.jpg
Views:	111
Size:	113.3 KB
ID:	292962   Click image for larger version

Name:	IMGP9635.jpg
Views:	104
Size:	87.9 KB
ID:	292963  
Philips210 is offline   Reply With Quote
Old 14th Feb 2024, 10:10 pm   #16
Maarten
Dekatron
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,284
Default Re: PM 5519 pattern generator

The spiral cut isn't usually a problem, but it won't hurt to check the capacitors. Small axial ones tend to dry out, though they usually don't short.
Maarten is offline   Reply With Quote
Old 14th Feb 2024, 10:33 pm   #17
Chris55000
Nonode
 
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,980
Default Re: PM 5519 pattern generator

. . .I've often come across what appears to be this "spiral cut" on Philips/Vishay axial electrolytics – its due to the sleeve being imperfectly wrapped round the capacitor in manufacture – clear adhesive tape wrapped around the capacitor will do until a replacement can be fitted – I've had them new from RS, etc., like this!

Chris Williams
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!
Chris55000 is offline   Reply With Quote
Old 15th Feb 2024, 10:19 am   #18
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

Malcolm,

Just to confirm, you did check that C590 68uF was not s/c?
In the attached pic, the jumper link which feeds the -12 supply to the current limit resistor R760 is shown. Note the fairly close proximity to the ground track connecting C68 +ve and C531 -ve.

Also a further correction to my post #9. It should be unsolder the GREY wire not the yellow one. The latter is on the other side of the switch so isolating that won't prove anything. It doesn't apply here though as the switch has been ruled out.

Regards,
Symon
Attached Thumbnails
Click image for larger version

Name:	IMGP9628.jpg
Views:	76
Size:	82.0 KB
ID:	292968  
Philips210 is offline   Reply With Quote
Old 15th Feb 2024, 12:45 pm   #19
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,664
Default Re: PM 5519 pattern generator

One other thing Malcolm. Perhaps you could take a few close-up pics of the board in the problem area. Also one on the solder side as well and post them here. We may be able to spot something.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 15th Feb 2024, 1:02 pm   #20
Malcolm G6ANZ
Octode
 
Malcolm G6ANZ's Avatar
 
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,048
Default Re: PM 5519 pattern generator

First the good news. I removed cap 533 and the -12v returned. As suspected the wrapping had a spiral gap in it. I replaced the cap.
Now the bad news. It seems that ,somehow, the IC 314 has died as there is only a small distorted output. The signal going in on pin 6 is OK but the signal on the link TP8/TP9 is only about 20mV.
More work required.
A big thanks to all who helped in this nasty fault. Standby for more questions!

Malcolm
Malcolm G6ANZ is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 3:08 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2024, Paul Stenning.