EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: mattswensson on May 22, 2023, 05:37:28 pm
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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 (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.
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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
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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.
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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.
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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?
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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.
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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.
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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!
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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.
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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.
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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.
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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 (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 :palm: and bring it back to my workshop.
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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.
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Thank you for the tips. Will definitely look through all these after I get mine reassembled.
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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.
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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 (https://www.digikey.com/en/products/detail/kemet/R82DC3470AA60J/2839160)
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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?
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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?
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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.
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Do you have an oscilloscope?
Yes!
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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?
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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!
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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.
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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.
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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.
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loglow, can you verify something for me? On the B board, at spot C124, do you have a polarized cap in that spot? I've attached an image and highlighted it green. The board is silkscreened bi-polar, but I'm just double checking that I'm not crazy as I pulled this cap and the photo I took prior is obstructed by a wire. :( The attachment also shows the orientation I recorded.
should be a 10uf 25v per the manual
The schematic of the 1371Q shows this as polarized with positive going to the IC102 pin 4 which is what I'm tracing as well on the 1271Q board.
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This makes me feel better about recapping my power supply board too.
I ended up doing this as I figured I was so deep in pulling this thing apart I might as well.
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Well, I recapped the whole rig except for a handful of bipolar caps on the Q board. I am still getting the same issue with the curved screen as in the attached photo.
I will review all the posts above and walk through the circuit. I have been testing voltages as outlined, but I've found all the RV's raise and lower voltages in/out of the TDA chip and Q806, so kind of hard to map to that.
UPin and NPin amps and phases all have SOME effect, the YBOW adjustment has little to no impact.
I did find that the IC501 and IC504 voltages are pretty spot on with the schematics.
I also want to hook up my oscilloscope, however I'm new at that equipment and have to identify the proper ground point so I don't ruin it. I also don't have an isolation transformer so I'm being extra cautious.
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Good pickup - replying quickly to confirm:
- I've gone back to my pre-recap photos and can see C519 is 1uf 50v BP; C818 is polarised
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Just seeing your second reply with things for me to action; my thoughts below:
My board also had a bipolar at C519, but the silkscreen is marked as polarized.
Stock capacitor in mine was BP
The service manual lists C526 as a tantalum. It's not an electrolytic cap on my board either.
I can't find it in my photos but in my checklist I've physically ticked YES to putting in a 3.3uF 25v electrolytic in C526s spot. Would be unlike me to desolder a tantalum in a recap job so I think it's fair to conclude mine had a 3.3uf 25v elec from factory.
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.
I can see this now and have triple checked - confirming 100uf 25v was there from factory and that is what I put in.
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.
You're right - my spreadsheet lists it as per service manual however in my checklist it's not ticked. Then saw in my photos nil component present from factory. I have deleted this row from the spreadsheet.
I don't think my board had a bipolar at C818 either, but I'll have to double check. The silkscreen marking was polarized.
See previous reply confirming C818 should be polarised; the confusion came from the adjacent C519
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.
Yes my photos show a film cap and an electrolytic in parallel; I probably didn't document this on the spreadsheet but did tick it off as done.
I've opened the latest supplied photo in full and it's more than a pin issue - I say this as my understanding was pincushion correct is last mile sort of thing; you don't have full horizontal deflection, far from it. Sure the is pin cushion issues but why is the raster 3/4 wide
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I've opened the latest supplied photo in full and it's more than a pin issue - I say this as my understanding was pincushion correct is last mile sort of thing; you don't have full horizontal deflection, far from it. Sure the is pin cushion issues but why is the raster 3/4 wide
If you are referring to my photo of Rockman 5 video game, I actually decreased the horizontal width just so it is clear the extent of the curve. When I grow it back to the width of the screen, the problem is still there, but it is kind of 'clipped' off screen so that is the reason for my decrease in width. I really need to get the grid on the screen which I'll try to do this weekend.
Thanks again for everyone's help and guidance. Hopefully we can both get our issues resolved.
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Or maybe you are saying that this is so severe it isn’t a pincushion thing because that is more of a slight tweak?
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If you are referring to my photo of Rockman 5 video game, I actually decreased the horizontal width just so it is clear the extent of the curve. When I grow it back to the width of the screen, the problem is still there, but it is kind of 'clipped' off screen so that is the reason for my decrease in width.
The good news is that your “Normal H width” trimmer is causing the screen image to get narrower and wider. This confirms that most of the pincushion circuit is functional.
Check down a few posts in this thread for my description of the signal path.
The pincushion circuit requires a “ramp” (sawtooth) input signal which originates from the horizontal/vertical oscillator IC. This IC is still functional because both horizontal and vertical deflection are present.
Therefore the most likely fault is with this vertical frequency ramp signal failing to get all the way to the pincushion IC.
The ramp signal itself is at 60Hz (50Hz for PAL/SECAM modes) and its amplitude probably about 1V.
The best way to follow its progress is with an oscilloscope.
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Awesome...so I want to hook up my oscilloscope without frying it. This rig seems to have earth ground and the ground plane all going to the same place (?)...I assume I need an isolation transformer before I hook my scope up correct? or is there some ground point on this machine I can safely leverage.
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UPin and NPin amps and phases all have SOME effect, the YBOW adjustment has little to no impact.
The N-pin-amp trimmer should have a considerable effect on the )-|-( vs. (-|-) curvature at the extreme left and right edges of the screen. The “N” trimmers may interact with each other. Getting perfectly straight left and right edges may require several rounds of tweaking.
It is logical that all “N” trimmers should get adjusted first. Then switch to “underscan” mode and adjust the “U” trimmers. I would expect the “U” trimmers to have no effect when the normal/underscan switch is set to “normal.” One of my thoughts is the “normal/underscan” switch might need its contacts cleaned. If the “U” trimmers are changing the shape of the screen image while switch is at “normal” then this portion of the circuit needs more attention.
As for the “BOW” trimmers I think they provide a very small adjustment to make a vertical line located in the middle of the screen perfectly vertical. These “BOW” controls are not part of the pincushion circuit. Rather they do something with the timing of the sync signals. My best guess is that BOW should have this effect: At one end of rotation: (-(-(. In the middle: |-|-|. And all the way at the other end of rotation: )-)-). This is likely to be a very small effect. Perhaps only a few mm deviation from perfectly vertical.
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Awesome...so I want to hook up my oscilloscope without frying it. This rig seems to have earth ground and the ground plane all going to the same place (?)...I assume I need an isolation transformer before I hook my scope up correct? or is there some ground point on this machine I can safely leverage.
Most of the circuitry in this monitor is isolated from the AC mains.
However, the input section of the main power supply has “live” AC mains voltage everywhere.
In a unit of this complexity there could also be “live” mains AC in unexpected places. Therefore I consider an isolation transformer to be essential for bench testing this type of item, especially in cases where I am unfamiliar with the item I am testing.
To confirm line isolation use an AC voltmeter with a 10K resistor connected in parallel with the meter. One probe to a good earth ground. Other probe to the circuit ground of the monitor. Residual AC voltage should be <2V or so.
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I haven't had the chance to dig into scoping IC501 yet, but I'll be able to soon hopefully!
I've nearly finished recapping my set now, and in doing so I've revised the BOM a lot, including adding board B which I'd omitted previously. I believe it might be final at this point, or close to it. While pretty close, neither of the component listings in the available scanned service manual perfectly match the set that I have, which is what these lists are all based on.
Attached is a PDF which is easy to read and contains some basic notes where needed, a table that maps reference designators to boards, and a table with board totals.
Also attached is a CSV which can be easily uploaded to distributors. It's been zipped since CSV files aren't allowed as attachments here.
Both of the attached files were generated from my Google Sheet here:
https://docs.google.com/spreadsheets/d/1YE-vZhxJ-iNjr-vr_YdPARD5g_YhLzjlOWTg84AWAdU (https://docs.google.com/spreadsheets/d/1YE-vZhxJ-iNjr-vr_YdPARD5g_YhLzjlOWTg84AWAdU)
Finally, here's a link to the list on Digi-Key:
https://www.digikey.com/en/mylists/list/7O0SY5C4OK (https://www.digikey.com/en/mylists/list/7O0SY5C4OK)
As of right now, all the components are in stock with active status, and the total price is $64.86.
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loglow, can you verify something for me? On the B board, at spot C124, do you have a polarized cap in that spot?
Well, I unfortunately can't confirm what was there previously, but I can confirm that my board also has it marked as bipolar.
In general, there's no harm in using a bipolar cap in place of a polarized one. The danger is using a polarized cap with its polarity reversed or installed where the use of a bipolar one is necessary. So it should always be okay to use a bipolar cap if there's any doubt.
For example, I'm pretty sure there was a polarized cap in the (unmarked) position that I've named "C1R102" but since there are no board markings there at all, I'm putting a bipolar cap there just to be safe.
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Hi all,
Not sure if a solution to OP's problem was found after this thread died but if not I would like to continue contributing to the eventual solution. This seems like a very common failure on this model but nobody online has posted a solution and the general advice of recapping does not fix it.
I am working on a 1271Q with the same problems OP has. For anyone else working on one, you should use the 1371QM service manual (https://crtdatabase.com/crts/sony/sony-pvm-1271q). This is the exact same monitor as the 1271 but the West Germany variant, and the manual scan is MUCH BETTER. It also includes all of the waveforms.
I have checked around the entire IC804 pincushion controller and all of the incoming and outgoing waveforms are fine. The vertical saw wave comes all the way from IC504 Pin 7 to IC804 Pin 10 (you will need to really zoom your scope for this, the waveform is only 0.6vpp). All the voltages are close enough that I don't suspect anything wrong either. I tried replacing the chip with a known good one and the problem remains the same. I have replaced all of the critical caps in the pincushion circuit (C841, C843, C844, C871). I checked Q806 (2SD1138 on the output of IC804) and it tests fine.
The pinamp potentiometers mostly don't work - but they work a little bit better in underscan mode. Nothing looks the way it should but I can at least see some changes when I turn the underscan ones. In normal scan barely anything changes no matter what I do.
This behavior leads me to believe there is something wrong with the horizontal width, not the pinamp circuit. Like maybe the horizontal circuit B+ is low, or maybe the pinamp output bias is wrong.
I will continue to update this as I find out more.
Edit: I checked all voltages and waveforms going in and out of IC501, which is the sync processor. It creates the horizontal drive signal. Everything in and out of it is normal.
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Thanks so much for your reply!
I've had to put mine aside for a bit, but I'm still excited to eventually work on fixing it again.
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I got in contact with someone who has a properly working 1271Q ... they are going to let me borrow it for research purposes. I will compare voltages and waveforms with the failed one I have here and maybe we will finally get some answers.
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I appreciate the information. It sounds almost identical to what I originally posted. I also had to put mine to the side because work ramped up but will be diving back in in the coming weeks.
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OK I have spent more time than I ever wanted to on this... But I finally have some news/info to share. It's not a solution yet but it feels like I am closer. Sorry in advance for the huge images but it doesn't seem like this forum supports width parameters on image embeds, and doesn't have a spoiler tag for hiding large content.
First I had to narrow out the possibility that I had gotten a bad replacement IC804 from eBay, or that my Q806 transistor was somehow failing. In order to rule that out, I took working copies of both parts from a working 1271Q and swapped them into the bad 1271Q. There was no change. This means a IC804 with no output is a sign of bad inputs - NOT a failed IC.
* The Q806 output waveform is CRUCIAL. It can be observed with an oscilloscope at the collector of Q806. A working 1271Q will have a drape-looking 60Hz ~8 vpp (base ~38v) wave. Eventually I will share all of my waveform images I took, but for now I just want to focus on the relevant ones (see bottom of post).
* If you see either nothing or some kind of 15Khz waveform as the Q806 collector output above, then your pinamp IC is not outputting anything. You're just looking at noise.
So why isn't IC804 outputting anything? First we need to understand how IC804 works. It is a TDA1082, and looking at the datasheet you can see the main inputs are pin 10 and 11, which go into a differential amplifier. Think like an op-amp. Sony's implementation of this IC in their pinamp circuit is almost a direct copy of the example circuit in the datasheet - they just eliminated the trapezoid adjustment, added an external VBOW/VANG adjustment on pin 7/8, and added a (pin) phase shift adjustment on pin 11.
I arranged all of the "good" 1271Q waveforms on the datasheet so we can better understand how they work together:
(https://crtdatabase.com/downloads/images/tda1082_good.jpg)
The main players here are the inputs on pin 10 and pin 11. Pin 10 is a sawtooth waveform coming from the vertical oscillator, its amplified and output from IC504. Not only does this wave need to make it all the way to IC804 pin 10, but its amplitude, offset, and all other characteristics are EXTREMELY important. If they are off even a little bit, it is enough to cause IC804 to stop outputting. The problem with all of these 1271Qs, at least my guess, is that this waveform is malformed from one or more other components failing.
When this waveform is wrong, and IC804 stops outputting, it heavily biases the entire horizontal width circuit incorrectly, which is why your raster width becomes squished and the N H WIDTH control barely does anything anymore.
I was able to prove some of my hypothesis by desoldering ('floating") pin 10 of IC804 to take the bad waveform input out of the equation. If you do this on your bad 1271Q, and my hunch is correct, your N H WIDTH pot should start working again and you should be able to get full raster width - you just won't have any working pinamp adjustments.
One of the first things i did when starting diagnostics comparisons between a good and bad 1271Q was compare every single pin's waveforms on IC804 - so why didn't I notice anything wrong with Pin 10 early on? It seems the problems are only evident when you FLOAT THE PIN first to take it out of circuit with the rest of the pinamp circuit. This allows you to view the unaltered input waveform before it gets coupled to anything else further down the circuit. Once I did a floated pin 10 comparison between the two PVMs, the differences were obvious. The bad sawtooth waveform has what appears to be a variable DC offset, it slowly drifts up and down on my scope by several volts, and it seems very noisy/jumpy. On the good PVM, this waveform is rock-solid with no drifting or jumping.
Here is what a good pin 10 input waveform should look like when floated from the IC input (i.e. I took the measurement from the empty pad):
(https://crtdatabase.com/downloads/images/ic804p10_good_floating.jpg)
Generally if I see weird DC offsets I would blame a capacitor - but there are people in this thread who have already recapped their whole 1271Q and didn't solve the issue. Personally I have replaced every electrolytic (they were all within spec) and manually checked every ceramic/film capacitor on Pin 10's circuit (they were all fine) - this made absolutely no difference to the problem. Pin 10 is coupled to the VBOW/VANG circuit at C522, which I have not recapped. I suppose the problem could be down there, but those adjustments seem to be working fine and that area of the board is not particularly easily accessible so I am avoiding that for now.
So with all of that in mind, I am pretty clueless right now on what the problem component could be here. For research purposes I actually tried to eliminate the DC offset myself by adding a ceramic capacitor in series right before Pin 10 of IC804, and the results were fascinating. Once I eliminated the DC offset, IC804 woke up and started outputting a waveform via Q806, and I was able to freely adjust N H WIDTH, PIN PHASE, and several other adjustments. The pinamp distortion improved significantly too. However, this is not a solution because the waveform, although present now, is still not correct when compared to the good PVM - and this is why the geometry is still wrong. Here is what I see on screen:
(https://crtdatabase.com/downloads/images/bad_waveform.jpg)
Here is what the incorrect Q806 collector waveform looks like that generated that output on the screen:
(https://crtdatabase.com/downloads/images/bad_Q806_collector_with_capacitor.jpg)
And here is what a perfect waveform at Q806 collector looks like, for reference. This is the magic sauce:
(https://crtdatabase.com/downloads/images/good_q806_collector.jpg)
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This is super helpful. I’m going to scope mine again and see what I’m getting. I have found a couple locations that don’t match the apparent spec and will report back.
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This is super helpful. I’m going to scope mine again and see what I’m getting. I have found a couple locations that don’t match the apparent spec and will report back.
That would be great. I am particularly interested in what your IC804 pin 10 waveform looks like (first normal/connected and then with the pin floated), and what your Q806 collector looks like before and after floating pin 10.
I am expecting once you float pin 10 you will be able to adjust horizontal width.
If you couple pin 10 to the input signal via a 4.7uF ceramic capacitor you'll be about where I am right now. I noticed the datasheet example circuit uses a 100uF capacitor so I'm going to give that a shot too and see how it changes the waveform. I am really curious where this 5v DC offset on my sawtooth waveform is coming from...
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Hold the phone, I just fixed the problem entirely on my 1271Q and the fix is so simple it actually physically hurts me how deep I dove into this. The N PIN AMP RV805 potentiometer on mine went bad. The literal first thing I did for diagnostics was cleaned all the pots with deoxit to rule out dirty/bad contact on the exposed surface pots but of course this pot is broken in some other physical manner that Deoxit won't fix. Its resistance has drifted from 0-330ohms range -> 100K to Megaohms range. I replaced it with a 150ohm pot I had laying around and everything immediately was corrected (to the extent 150ohms can - I need to find a full 330 range pot to correct the pinamp the remaining amount). The waveform out of Q806 looks great now, the raster width fills the whole screen, and I have control of pincushion adjustment. :rant: :palm:
So to everyone with this problem - CHECK EVERY D BOARD POT OUT OF CIRCUIT, STARTING WITH THE N PIN AMP AND U PIN AMP. PULL THEM FROM THE BOARD AND MEASURE THEIR MIN AND MAX RANGE. If they don't fall within the range on the schematic, throw them away and get new ones. God I want the last 3 weeks of my life back :-DD
Edit: I posted more repair info here on my website: https://crtdatabase.com/crts/sony/sony-pvm-1271q#repair-notes
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This is great news! I will try this asap and report back as well. I think/hope I have some pots that will fit!