Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-17-2013, 02:15 PM   #1
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
TTL Meter Repair?

Hello folks, i just got myself a 6x7 w/ TTL Pentaprisma.
Builit quality is amazingly solid though sadly enough, the meter only works when the lens is stopped down, and even then, kind of crappy.
Readings fluctuate wildy, and the needle goes way off on the slow times (>1/8s).
From what i gathered so far from different existing threads, the problem seems to be the capacitors.
I have the version with 2 circuit boards (one on each side of the prisma ), serial # 52XXXX. I guess thats the old version?
Can anyone please tell me the values of the capacitors or even provide me with a copy of the service manual?
From what i have seen so far, having not entirely stripped it apart, it has 5 small variable resistors and a big one (more than i have ever seen on any exposure meter).
How do i calibrate once i have the capacitors replaced?
Loads of thanks in advance !!!

04-17-2013, 02:22 PM   #2
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
cannot edit my posts yet, so here a p.s.:
i already cleaned the contacts from body to meter, the chain is working and running smoothly, and i put on the lens and meter in correct order.
04-17-2013, 02:44 PM   #3
Veteran Member
Silent Street's Avatar

Join Date: Nov 2011
Location: Geelong & Richmond, Vic AUS
Posts: 529
It sounds like there could be a problem with the shutter speeds on the camera and and below 1/8, not solely what the TTL meter is determining.
Nobody would begrudge you having a go at the meter as a DIY task, but given the age of these things, you could probably save yourself a lot of trouble and angst by sourcing a new TTL meter from the auction site; many are new and unused, among other variations (chimney finders, waist-level finders...).
04-17-2013, 03:02 PM   #4
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
Well, the times themselves seem about right (for a mechanically timed shutter, that is).
I mean the TTL Pentaprism does not influence the shutter speeds itself anyway, it's just a match needle system for the 6x7, unlike the 67 II with its apertury priority option..
What i meant by "the times below 1/8 seem off" is that the match needle on longer speeds actually REVERSES and goes back towards the underexposed side of the indicator scale, which obviously cannot be right.
The reason for me to give it a try to fix it, is that i am fairly good at soldering (the circuit boards are nicely laid out and sparsely populated, no fidgety SMD stuff here), while my funds are fairly low at the moment due to the dreaded GAS.

04-17-2013, 03:41 PM   #5
Site Supporter




Join Date: Jun 2011
Location: Texas
Photos: Gallery
Posts: 1,142
If you are located in the US you could also check with Eric Hendrickson - his repair costs are VERY reasonable, and he does work on 6x7s. If you send it to him he will give a free estimate, and return it if you decline. I had him go through my 6x7 and have been very pleased.
(I had another well-known tech do a CLA on my Hasselblad. Also a good job, but the cost difference....!)
04-17-2013, 04:07 PM   #6
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
Well, as I am based in Germany, shipping costs alone to almost anywhere + work hours would be prohibitively high in comparison to getting a "new" meter from some auction web site. Besides, I actually like to fix camera stuff, last thing I did was a electro-mechanical copal #0 shutter, now that's quite small and fumbly, so once I know how it is done, that pentax meter should not pose a huge problem for me.
04-17-2013, 04:22 PM   #7
Giveaway winner!
MysteryOnion's Avatar

Join Date: Dec 2007
Location: beantown
Photos: Albums
Posts: 921
Consider... since your location does not look to be near the US... clean all contact as well as the mounting stops to the side of the finder bay.

QuoteOriginally posted by blablub Quote
Can anyone please tell me the values of the capacitors or even provide me with a copy of the service manual?
Commonly if you have the usual manual, it is only of the first version and the circuit was greatly modified for the second and later versions. The "variable" resistors...
Potentiometers? Check the 'Pot' that is directly related to the chains index. Located in front of the prims, it serves too functions. First as the variable resistance and second to allow stop-down for the lenses that have not TTL metering index. The other possible fault in the circuit is the capacitors.

04-17-2013, 05:16 PM   #8
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
well, my meter came fairly well-worn-looking on a 6x7 non-MU, so i presumed that was the "kit" one, first version, and that it was not interchanged with a later, updated version. As you can see in the attached picture, the circuit boards on my meter look quite different to yours, and there is a second board as well, with its wires leading to the right (seen from the top like in my pic) contacts on the base.
Pot #1 is a big one, pots #2-5 look alike, pot #6 is obviously different again. From the other meters i have seen so far, i would presume #1 controls the overall level, #2-5 control the upper/lower limit for each stopped-down and open-lens metering....so what would pot#6 be for?
Without de-soldering, i cannot really make out any readable value on the capacitors, (some of them look like having only 2 color bands and i am not entirely sure of a few colors, if they are supposed to be brown, gold or orange), and obviously i do not wanna screw things up more than they already are.
Sooo, i hope someone can shed some light (haha) on that situation here !

Attached Images
 
04-17-2013, 05:21 PM   #9
Giveaway winner!
MysteryOnion's Avatar

Join Date: Dec 2007
Location: beantown
Photos: Albums
Posts: 921
I'll stiff my notes and see what I have.
04-17-2013, 05:32 PM   #10
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
thanks a lot for any help !
04-17-2013, 05:41 PM   #11
Veteran Member
Silent Street's Avatar

Join Date: Nov 2011
Location: Geelong & Richmond, Vic AUS
Posts: 529
Very interesting re the construction differences between the old 6x7 and the newer 67 prisms. I worked in electronics repairing televisions (value technology, no integrated circuits I can remember back then) and can recall very rudimentary, often crude circuits like those in the first meter dissection. The second picture is a much more modern and intriguing affair of electronics and somewhat strange looking capacitors of reds, blues and yellows which probably will tell you immediately what their values are. I'm wondering how reliable this circuit is over a long period of time, and if it is a nasty jolt or drop that ultimately determines when an active service is required. Fascinating stuff.
04-17-2013, 06:13 PM   #12
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
hmm....correct me if i am wrong, but i think MysteryOnion's meter is the more modern one: it has two ! fancy ICs...whereas mine has only one "boxy" looking part inscribed e4a-t1 (and i couldn't find any ic bearing that name). The royal PITA for me is that the capacitors' color codes have, due to age, become quite hard to decipher, because of flaking paint (which looks like some poor sod had to apply it by hand btw....oh yeah and the soldering job is actually not too great either, but i don't want to resolder the entire board in order to rule out bad joints).
Anyway, it's 3 am here now, enough with camera gear depriving me of my sleep
04-18-2013, 11:33 AM   #13
Inactive Account




Join Date: Apr 2013
Photos: Albums
Posts: 9
Original Poster
Thx for the advice everybody, i got it to work !
I applied liberal amounts of contact cleaner to the wipers of the aperture pot, the asa pot and that little pin sticking out in the 3 o'clock position (in front of the lens release lever). I can't compare because i only have the 105mm and no non-auto-aperture lenses, but I suppose that pin leads to a switch to let the camera know what kind of lens it is?. Resoldered a few dodgy looking wires, and now it works again.
The needle is a bit sluggish, but i guess that's kind of normal in such an old meter.
After all, about an hour of work including cleaning out loads of rotten foam, no big deal.
04-19-2013, 06:46 AM   #14
Giveaway winner!
MysteryOnion's Avatar

Join Date: Dec 2007
Location: beantown
Photos: Albums
Posts: 921
I'm trying to find the data on the "false signal" arresting circuit use in my version... due to the high commotions here in Boston that I've been distracted.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, medium format, meter, ttl, ttl meter, version
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
TTL meter not responding with Extension tubes fabian628 Pentax Medium Format 17 05-18-2012 06:03 AM
Pentax 67 TTL pentaprism meter problem? bienemaya Pentax Medium Format 9 04-24-2012 06:06 AM
TTL Meter not working lostlogo Pentax Medium Format 4 03-26-2012 12:40 PM
Pentax 67 TTL prism meter window not visible vmixer Pentax Medium Format 8 11-15-2011 07:54 AM
Repair Asahi SPII My Light Meter 3RiC Pentax Film SLR Discussion 3 11-02-2009 12:14 AM



All times are GMT -7. The time now is 11:59 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top