Electronics > Repair

Sony PVM-1271Q

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--- Quote from: mattswensson on June 10, 2023, 05:54:30 pm ---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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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.

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:

Finally, here's a link to the list on Digi-Key:

As of right now, all the components are in stock with active status, and the total price is $64.86.


--- Quote from: mattswensson on June 09, 2023, 04:40:38 pm ---loglow, can you verify something for me?  On the B board, at spot C124, do you have a polarized cap in that spot?
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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.

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. 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.

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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