Sony PVM-1271Q

[mattswensson]

Hello, I'm working on a recently picked up Sony PVM-1271Q.  It has been noted that the online service manual for the 1271/1371 is lacking some information - I'm specifically looking for the waveforms for this monitor so I can hook up my scope and see what's going on.  Does anyone have these waveforms available or should I expect them to be similar to another model that waveforms are available?  Service manual https://archive.org/details/sony_PVM-1271Q_Service_Manual

The problem this monitor is exhibiting is significant pincushion that the pots can't seem to rectify.

I've found that pin 13 of the TDA1082 (IC804) is running at 6.7V vs the 3.4v specified in the schematics which traces back to multiple places include Q806 (2SD1138) that is outputting about 37v vs the 35.1v noted in the schematic and Q807 which is showing 4v instead of 2.4v.  Interestingly when I test voltage on Base (Input) of Q807 (DTC124ES) where there should be 0v (but is showing 1.4v), the pincushion gets impacted in a positive way.

So I'm narrowing down to possibly Q807 needing to be replaced - unless i'm being fooled which is a definite possibility because, well, i'm no expert on this and am still learning.

Anyway, any help or additional literature is appreciated.

I plan to get an NTE2357 to replace the DTC124ES as I'm reading they are equivalent.

[loglow]

Hi Matt,

I'm in a very similar situation! I have one of these with very bad vertical bowing that I can't correct, and I suspect it's due to a fault.

I probably won't be of much help to you, since I don't really know what I'm doing, but perhaps we can help each other out.

I'm frustrated that the available scan of the service manual is incomplete and appears to be a combination of several different versions of service manuals. For example, it doesn't appear to contain sections 3-3-1, 3-3-2, or 3-3-3 at all. It also contains two different variations of section 6. (Side note: Do NOT buy the service manual from ServiceManuals.net because they are just selling the incomplete one you can get for free from https://archive.org/details/sony_PVM-1271Q_Service_Manual so I'm filing a chargeback.) Edit: ServiceManuals.net is indeed selling an accurate scan (and nice quality too, superior to the version on archive.org) of the real service manual with part number 9-963-325-01. The problem is that this service manual appears to have a severe printing error affecting pages 23-46 and a huge amount of the content is entirely missing from it.

The first thing I'm planning to do is replace all the electrolytic caps on the D board, since that seems like low hanging fruit. The two parts lists mostly agree with each other, although there are two different values for C535. I'll have to check mine and see which value it is.

Anyway, here's my spreadsheet with all of the D board capacitors listed, and all of the differences between the two parts lists (this is the "Caps" sheet). Edit: The link below is now a sheet with all of the electrolytic caps (for all boards) listed.

https://docs.google.com/spreadsheets/d/1YE-vZhxJ-iNjr-vr_YdPARD5g_YhLzjlOWTg84AWAdU

The "Elects" sheet is a list of just the electrolytic caps that I'm going to replace first, including the part numbers that I picked on Digi-Key.

Best,
Dan

[jeremybh1]

Figured I should chime in here - I run hobby business Full Service Recap in Australia.
I can see a USA model number but should be the same.
I have the SONY PVM-1371Q in my personal collection and decided to 'fully' recap it and document this on my Excel spreadsheet. 

I don't share these widely but the eevblog is a good crowd and you may access it here: https://1drv.ms/x/s!AsalaOQMQ1R_gitfDNBGHleKgRJS?e=Ce5jsJ

While I was liberal in replacing the 38 year old capacitors; I left some as stock on the input terminal side only.  Quite a few were 'dead' and some photos are available showing >40 ohms ESR or totally open. 
We know ESR is only one 'thing' in caps - if they are leaking current and saturating a transistor then things aren't switching properly. I say this as your stated bad vertical bow could be as simple as a bad TDA chip - just work your way back in that section and recap it if replacing the IC. 

[mattswensson]

Thanks to both of you.  I'm in the middle of a full recap and realized that the schematics don't seem to call out the bipolar caps well (or I missed it).  So i'll be placing another order.  And I missed the cap on the tube neck.

So far, I've found one cap on D board that tested bad (C759), but will replace them all anyway and report back.

[mattswensson]

Jeremybh1, your sheet for Deflection board shows bipolar at C519, C529 and C818.

My D board has a bipolar installed at 519 and 529 but does not at 818.
By board is also silkscreened bipolar at 529, but not 519 or 818

I'm inclined to put a polarized cap in 818 given that is what mine has currently.  Did yours have bipolars in all those spots?

I've run into other scenarios where a bipolar can be used in some cases, but think I will start with replacing what I currently have.  maybe my board rev is different?

[loglow]

mattswensson, thanks for your notes and updates!

Jeremybh1, thanks for sharing your spreadsheet!

Some questions/comments:

• My board also had a bipolar at C519, but the silkscreen is marked as polarized.
• The service manual lists C526 as a tantalum. It's not an electrolytic cap on my board either.
• Jeremybh1, you have C535 listed twice, once as a 100uF and then again as a 1000uF. My board had a 10uF in this spot. The funky service manual lists this as 100uF in one place and 10uF in another.
• Jeremybh1, you have C537 listed as a regular 2.2uF. My board had this spot not populated. It's also marked as bipolar on the silkscreen.
• I don't think my board had a bipolar at C818 either, but I'll have to double check. The silkscreen marking was polarized.
• My board had other non-populated positions for caps too: C540, C874, C890, a polarized one with no ref near D501, and a bipolar one with no ref near L811.
• My board had an odd thing at C801: There was a 0.47uF film cap as expected, but there was also a 470 ohm resistor in series with a 2.2uF electrolytic cap, both of which were soldered in parallel to the film cap.

I did recap my whole D board today but the problem still remains (see attached photo).

I may try replacing the TDA chip next as you suggested. Is that the TDA1082 at position IC804? Looks like they're running about $8 each on eBay at the moment.

It seems like a great monitor so I'd really love to get it fixed up and looking correct.

[mattswensson]

loglow,

I was just logging on to ask about C801 as well.  I have the same scenario, a 2.2uf and resistor piggybacked on the C801 film cap.

Yes the TDA1082 is located at IC804.  Too bad the cap kit didn't fix it.  I assume you've tweaked all the trimmer pots in an effort to correct the pincushion/bow?

My NTE2357's showed up and I will likely swap out Q807 given the result I was getting.  I'm not convinced my TDA chip is bad yet because the input voltages are off leading me to think it is upstream, but I could be wrong.  I need to place another digikey order given I missed the bipolar caps, but am going to replace the other caps until then.

[loglow]

I assume you've tweaked all the trimmer pots in an effort to correct the pincushion/bow?

Yeah, I have. Neither of the "bow" pots have any effect, nor do a number of the others. Most of them do have an effect though.

My NTE2357's showed up and I will likely swap out Q807 given the result I was getting.

I'm curious to know what happens!

[elecdonia]

The pincushion circuit also controls the horizontal width. If entire pincushion circuit is totally non functional then the following controls will not change the horizontal width of the image at all.

Please try the following tests:

1) “Underscan” switch on the front panel: Does it have any effect on the horizontal width?
It should change both horizontal width and vertical height by about 10%. Height and width should both change by the same proportion.
2) Trimmer RV803 (N H SIZE):” Does it have any effect on the horizontal width? (This trimmer should be active for both positions of the “underscan” switch)
3) Trimmer RV806 (U H SIZE):” Does it have any effect on the horizontal width? (This trimmer is only active during underscan mode)

If any of the above cause the horizontal width to change then the output portion of the pincushion circuit is functioning.

[elecdonia]

Interestingly when I test voltage on Base (Input) of Q807 (DTC124ES) where there should be 0v (but is showing 1.4v), the pincushion gets impacted in a positive way.

Q807 is a "digital transistor." It expects a logic-level input. Its collector is either open circuit (for logic low input) or is grounded (for logic high input). In this circuit Q807 should be turned on only when the "underscan" mode is active. Q807 base voltage should be 0V for "normal scan" and perhaps ~3V for "underscan" mode.

Unfortunately the scanned SM doesn't include a schematic for the PC board with the user controls and switches. I do suggest cleaning the contacts of this "underscan" switch.

[elecdonia]

The input signal to the pincushion circuit (which actually makes it perform pincushion modulation) is a ramp signal (sawtooth) at the vertical frequency. This signal arrives at the junction of R855, R897, and C883. Signal amplitude at this point is likely ~1-2V.
C884 (330uF) is important: If it is open or high ESR then it won't couple the vertical ramp signal into IC804. But if shorted or leaky then it will mess up the DC bias voltage at the IC804 input.
Trimmer RV805 (N PIN AMP) is also important. When at minimum there is no ramp signal applied to IC804. This would cause the "pinched" appearance of the screen image. Increasing the ramp signal should make the image wider at the midpoint to correct the "pinching."
The ramp signal ends up on pin 10 of IC804 (TDA1082). I recommend checking pin 10 with oscilloscope. Amplitude is likely < 1V.

[elecdonia]

Assisting with diagnosis of this pincushion fault sent me off into a rabbit hole of attempting to understand the theory of operation of this circuit. Unfortunately all downloadable service manuals for the PVM-1271 are incomplete (OP mentioned this). Then I located a downloadable service manual for a (similar) Sony CRT monitor, the PVM-1341.

     https://www.manualslib.com/products/Sony-Trinitron-Pvm-1341-51779.html

This PVM-1341 service manual is complete, including adjustment instructions for pincushion. It contains 100's of 'scope waveforms too. But the PVM-1341 doesn't use the TD1082 pincushion IC. Instead the PVM-1341 contains a dual op-amp & several discrete transistors. That said, these two pincushion circuits are functionally identical. The trimmers, IC, and output transistor take a vertical frequency ramp signal as input and transform this into a "parabolic" current waveform which flows through the pincushion output transistor (Q806 for PVM-1271, Q507 for PVM-1341).

I found a TDA1082 datasheet (attached). It is specialized for "pincushion correction." Also known as "east-west correction." However, the Sony schematic doesn't resemble the circuit in the datasheet. Sony didn't use some sections of the TDA1082: pins 3, 4, 5, 9, 12, & 14 aren't connected.

I doubt the TDA1082 itself is the cause of the reported faults (however at >25 years of age one never knows... ). The TDA1082 is a low-level analog device operating at 12V. It isn't directly connected to high-power or high-voltage circuitry. Q806 interfaces it to the larger voltages/currents associated with the horizontal output stage & deflection yoke coils.

My personal curiosity is to learn how the current flowing through Q806 actually causes the horizontal width to vary. I attached an "application note" for a different pincushion IC. This app note describes all of the circuitry in detail. The section which interests me is the "diode modulator." I'm still studying it. Evidently a later version of the TDA1082 employed an internal PWM output stage instead of an external linear transistor (e.g. Q806). This is discussed in the app note. At this point I suspect raising the amount of current flowing through Q806 will increase the width of the image on the screen. But I'm not yet certain this is correct.

BTW I own a very similar 13" (or 14") Sony PVM monitor myself. I don't recall the exact model. I haven't used it for ~5 years but I remember it worked perfectly, delivering impressive picture quality for a CRT monitor. Now I need to remember where I stored it  and bring it back to my workshop.
 

[loglow]

Attached are some references I've made, in case they're helpful to anyone else:

The first document is a complete recap list encompassing all four boards (C1, D, F, Q) that have electrolytic caps, including widely available part numbers for each (all are currently in stock at Digi-Key). Some caps have been upgraded in terms of voltage rating in order to reduce the number of unique line items, but they're all equal or superior to the originals. It's easy to determine which board a cap is on based on the first one or two digits of its reference designator, so I've included a little chart for that too.

The second document is a list of all the adjustment points on board D, including their labels and locations, both on the schematic and the board layout print. Both the schematic and board layout print are included as well, with both the X and Y coordinates present and easy to reference, and each adjustment point is highlighted in red.

As a next step, I'm planning to go through each of the 20 adjustment points, both in normal and underscan mode, and record which ones have an effect on the image and which ones don't. I'm also planning to recap the three boards I haven't yet (C1, F, Q) for good measure.

Finally, I'm still attempting to obtain accurate and complete manuals, but I haven't had much luck so far. Part number 9-963-325-01 is the scanned service manual that's available in various places online which has a severe printing error that affects pages 23 through 46. The content of these pages appears to be an earlier revision of sections that already exist elsewhere in the document, with the intended content missing entirely. All the other pages (1-22 and 47-81) are correct.

I've identified the part numbers for all of the original service publications:

• PVM-1271Q Service Manual, part number 9-963-325-01 (This is the available scanned document with the severe printing error.)
• PVM-1271Q Service Manual, part number 9-963-325-11 (Content unknown. Perhaps this is a complete version without the error?)
• PVM-1271Q Supplement (S1), part number 9-963-325-81 (Content unknown.)
• PVM-1271Q Correction (C1), part number 9-963-325-91 (Content unknown.)
• PVM-1271Q Correction (C2), part number 9-963-325-92 (Content unknown.)
• PVM-1271Q Correction (C3), part number 9-963-325-93 (Content unknown.)
• PVM-1271Q Correction (C4), part number 9-963-325-94 (Content unknown.)

If I'm able to obtain any of them, I'll report back here.

[mattswensson]

Thank you for the tips.  Will definitely look through all these after I get mine reassembled.

[mattswensson]

That's great!  I'm working on cap maps for each board.  I've mostly completed the D board and the F board.  sample attached.  Will post fully when done.

[elecdonia]

I also think it will be useful to share a short list of critically important electrolytic capacitors on the D board. These capacitors will profoundly affect the performance of the monitor if they dry out (high ESR), or have significant DC leakage.

For pincushion circuit:
   C841    2.2uF    160V
   C844    330uF    16V
   C852  1000uF    25V

For horizontal deflection circuit:
   C860, C870              47uF      25V
   C827                       0.47uF  50V    (I recommend 63V "PET metallized film" type - see below)
   C854                       10uF     160V
   C855                       33uF     160v
   C825                       330uF     16V
   C527, C888, C873    470uF     16V
   C769                       47uF      25V

For vertical deflection circuit:
   C515            100uF   50V
   C846            330uF   35V

As noted above, when replacing small 50V electrolytics up to 2.2uF I recommend using 63V "PET metallized film" capacitors which come in compact "box shaped" packages. The Sony PVM-1271Q contains large quantities of these 0.47uF, 1uF, and 2.2uF 50V electrolytics. Tiny electrolytics frequently "dry out" and become open circuits because they contain only one drop of electrolyte. PET metallized film capacitors are reasonably affordable and will last longer than electrolytics. Example:

   https://www.digikey.com/en/products/detail/kemet/R82DC3470AA60J/2839160

[loglow]

Thanks for the recommendation, elecdonia! I'll revise my recap list with these film caps for the values you suggested.

I just tested all the adjustment points on my D board, except for RV802 which doesn't have a hole underneath it and appears to be otherwise inaccessible. Here are my results. "NO/EXP" means there were no visible changes but that's what I was expecting, whereas "NO" means that I would expect to see a change.

In short: The BOW and PIN controls are having no affect. Aside from attempting to replace the TDA1082, which I've ordered, any other suggestions?

[elecdonia]

Trimmers with prefix “N” (normal) should operate in both normal and underscan modes
Trimmers with prefix “U” (underscan) should operate only in underscan mode.
   Note: “Normal” scan mode must be adjusted first.

Because the horizontal width can be adjusted with the trimmers, this confirms:
   1) TDA1082 is at least partially functional.
   2) Pincushion output transistor Q806 is also functional.
   3) And the “diode modulator” circuit is also functional.

Next, because PIN AMP and PIN PHASE do nothing at all for either N (normal) or U (underscan) I suspect the vertical ramp signal is missing. I posted about this earlier. This signal originates in the horizontal/vertical oscillator IC. It travels through 1/2 of a 358 opamp. I don’t have the schematic in front of me right now but will provide details in my next post. Perhaps there is a broken/cracked foil or bad solder somewhere on the PC board?

Do you have an oscilloscope?

[loglow]

As noted above, when replacing small 50V electrolytics up to 2.2uF I recommend using 63V "PET metallized film" capacitors which come in compact "box shaped" packages. The Sony PVM-1271Q contains large quantities of these 0.47uF, 1uF, and 2.2uF 50V electrolytics. Tiny electrolytics frequently "dry out" and become open circuits because they contain only one drop of electrolyte. PET metallized film capacitors are reasonably affordable and will last longer than electrolytics.

The sweet spot here seemed to be up to 4.7uF, based on size, price, and quantity.

Also, there's no longer any need for the separate bipolar 1uF ones since all the PET film caps are bipolar.

My updated recap list is attached (I added a tolerance column), as well as a screenshot of the Digi-Key prices for them.

[loglow]

Do you have an oscilloscope?

Yes!

[loglow]

Next, because PIN AMP and PIN PHASE do nothing at all for either N (normal) or U (underscan) I suspect the vertical ramp signal is missing. I posted about this earlier. This signal originates in the horizontal/vertical oscillator IC. It travels through 1/2 of a 358 opamp. I don’t have the schematic in front of me right now but will provide details in my next post. Perhaps there is a broken/cracked foil or bad solder somewhere on the PC board?

Based on my limited knowledge and looking at the schematic, I'm guessing this might have something to do with IC501 (µPC1377C, V-H OSC)? It looks like the V OSC signal goes out pin 18 and into IC504 (µPC4558C, V SAWTOOTH BUFFER) -- is this the opamp you were talking about?

[vk6zgo]

As noted above, when replacing small 50V electrolytics up to 2.2uF I recommend using 63V "PET metallized film" capacitors which come in compact "box shaped" packages. The Sony PVM-1271Q contains large quantities of these 0.47uF, 1uF, and 2.2uF 50V electrolytics. Tiny electrolytics frequently "dry out" and become open circuits because they contain only one drop of electrolyte. PET metallized film capacitors are reasonably affordable and will last longer than electrolytics.

The sweet spot here seemed to be up to 4.7uF, based on size, price, and quantity.

Also, there's no longer any need for the separate bipolar 1uF ones since all the PET film caps are bipolar.

My updated recap list is attached (I added a tolerance column), as well as a screenshot of the Digi-Key prices for them.

Back when I fixed Sony BVM & PVM monitors  4 days out of 5, the very low value electros were pretty much unobtainium, & I routinely replaced them with film caps---with nary a problem.
We used all those monitors "In house", so I would have known if there were any!

As we were part of a large TV network, we pretty much got "champagne service" from Sony on their own special parts, but the low value caps weren't part of that.

Japan seems to have been awash with the low value electrolytics, as they pop up in just about every bit of gear from the 1960's through to the early '90s.

Of course, they are not the only ones with strange electros.

A BW Electrohome came in, with collapsed vertical scan.
The problem was the filter cap on the power supply to the vertical output, which was obtained from the rectified output of an "overwind" on the Horizontal output transformer.

For reasons of their own, the denizens of the "Great White North" used a bipolar electrolytic in this spot, which was "dead as a doornail".
Farnell had some bipolars of what looked like similar characteristics, so I ordered some.
I was surprised at how much smaller they were and marvelling at the onrush of technological progress, fitted one.

On turn on, up came the Electrohome with perfect vertical scans, as I congratulated myself, for all of 10 seconds, till the vertical collapsed again,along with a hissing sound & ominous vapour coming out of the cap.

It seems that the big cap was both bipolar & low ESR!

I ended up replacing the cap with a "Christmas tree" of "Polyester Greencaps", which did the job without flinching.

Pretty?---No, but functional?, Yes!

[loglow]

Back when I fixed Sony BVM & PVM monitors  4 days out of 5, the very low value electros were pretty much unobtainium, & I routinely replaced them with film caps---with nary a problem.

Great to know! I suspect these film caps are probably a lot cheaper than they were back in 1984 when the PVM-1271Q was being made.

The problem was the filter cap on the power supply to the vertical output, which was obtained from the rectified output of an "overwind" on the Horizontal output transformer.

This makes me feel better about recapping my power supply board too.

[elecdonia]

Based on my limited knowledge and looking at the schematic, I'm guessing this might have something to do with IC501 (µPC1377C, V-H OSC)? It looks like the V OSC signal goes out pin 18 and into IC504 (µPC4558C, V SAWTOOTH BUFFER) -- is this the opamp you were talking about?

Yes! The vertical frequency ramp signal comes from pin 18 of IC501. The opamp itself is a simple DC-coupled unity-gain follower. Therefore the AC signal amplitude at opamp output (IC504 pin 7) should be the same as pin 18 of IC501.
Then the buffered ramp goes into one end of R855 (330R). The other end of R855 connects to + of C844 (330uF). When probed at the junction of R855/C844 the AC signal voltage should be 1/2 of the original signal. Also the DC voltage at all of these points should be approximately 7V DC (as noted on Sony schematic.)

The same AC signal amplitude should appear at both ends of C844, but the DC voltage at the - end of C844 should be close to 0V.

The AC ramp signal amplitude probed at the wiper of trimmer RV805 should vary smoothly over the rotation of the trimmer. At one end of trimmer rotation the AC ramp signal should be 1/2 of the original ramp amplitude as seen at pin 18 of IC501. Rotating trimmer to the other end stop should reduce AC ramp amplitude to 0V.

[elecdonia]

The sweet spot here seemed to be up to 4.7uF, based on size, price, and quantity.

I fully agree with you. Although I occasionally use 4.7uF 63V PET film capacitors, they don't always fit the available PC board space. Also they cost more than high-quality 4.7uF electrolytics. But for replacing electrolytics of 2.2uF or less I nearly always use these 63V box-type metallized PET film capacitors. It leaves me with the feeling that the repaired item will be a bit more reliable than it was to start with.