Commodore 1702 Monitor Problems

[wildstar87]

Was wondering if anyone had any ideas on what's causing this horizontal line distortion on this monitor.  Was working, but now I'm getting this.  I do have a service manual, but definitely not familiar with CRT troubleshooting.

 

 

 

 

[Bratwurst]

http://easkcom.blogspot.com/2012/05/why-tv-retrace-lines-occur.html

 

Looks like vertical is overdriven. Probably need to replace caps related to the vertical circuit.

[+Nezgar]

Are the lines moving/jittering, or fixed/stationary?

 

I wonder if you play with the vertical adjustment knobs. IIRC some can be adjusted without opening:

[_The Doctor__]

@wildstar87

Clean everything while you are in there, dust, dirt, pots, etc.

Touch up an bad solder joints first thing. Expansion and contraction over the years cause cracking of the joints, say make sure ALL of them everywhere are good. After that...

Capacitors and power supply sections should be looked at firs thing, after that it's the normal course of troubleshooting.

It looks like retrace lines developing, retrace lines are caused by Capacitors becoming weak. I would highly recommend replacing the electrolytic caps after the initial clean up and touch up.

any other strange noises, crackling and hissing that are out of the ordinary when you are done is another issue that hopefully you won't need to tackle

Edited September 7, 2021 by _The Doctor__

[wildstar87]

12 minutes ago, Nezgar said:

Are the lines moving/jittering, or fixed/stationary?

 

I wonder if you play with the vertical adjustment knobs. IIRC some can be adjusted without opening:

Lines are moving, and jittering, though they seem to slow down as it warms up.

[_The Doctor__]

please read my post, messing with all the control will just take all the adjustment out of whack, a temporary brightening of the picture will sometimes help but it will fail in short order...

[Mclaneinc]

And remember, it's a CRT so treat it with respect, very high voltages on the tube..

[TGB1718]

14 minutes ago, Mclaneinc said:

And remember, it's a CRT so treat it with respect, very high voltages on the tube..

Even when it's off ☠️

[Mclaneinc]

5 minutes ago, TGB1718 said:

Even when it's off ☠️

Indeed, you don't want to discharge it with your fingers at any time

[_The Doctor__]

Yes and warning! Boiling water can burn your legs! Fire is hot! Ladders can be unstable! Falling from a ladder- bad for your health! Placing plastic bags over your head can lead to suffocation! Drinking random chemicals may harm you!

zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzt! Clear! Charging! Clear! zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzT!  beep beep beep beep beep

Edited September 7, 2021 by _The Doctor__

[Mclaneinc]

That coffee too strong Doc

[mattsoft]

@wildstar87 if you need help replacing caps, let me know -- I'm in Seattle and have recapped many 1702s and am happy to help ya out.

Edited September 8, 2021 by mattsoft

[wildstar87]

Thanks for all the suggestions, I'll take a closer look by this weekend. 

 

@mattsoft  Thanks, I don't have a problem with doing that, is this a typical symptom of caps?

[mattsoft]

8 minutes ago, wildstar87 said:

Thanks for all the suggestions, I'll take a closer look by this weekend. 

 

@mattsoft  Thanks, I don't have a problem with doing that, is this a typical symptom of caps?

I'm no expert on these things, but 30+ year old electrolytic capacitors, especially those that are near something hot like the components inside a CRT, are usually a good place to start and eliminate from the equation. Another simple thing would be to lubricate all adjustment pots with deoxit; I've seen strange behavior (like sudden brightness/dimming) because of scratchy pots. This is just basic maintenance, and if you haven't done that, well... start with the basic maintenance first.

Edited September 8, 2021 by mattsoft

[_The Doctor__]

yep, basic clean up maintenance, re cap... listen and look for other issues... then you can get out the fine tooth comb and calibrate if you like... my original post in a nutshell. Re trace lines should be gone then.

Edited September 8, 2021 by _The Doctor__

[wildstar87]

Got around to pulling this all apart today.  Was going to start ordering caps, but have a question.  Any reason to not use ceramic caps to replace electrolytic caps, if value, and voltage ratings are equivalent?  I'm thinking they will last much longer, and have more stability.  It seems that most signs say yes, but low ESR of MLCCs might cause issues, but not sure if this in this case would be any concern.  I also may already have them on hand.  Anyone done this?

[mattsoft]

15 hours ago, wildstar87 said:

Got around to pulling this all apart today.  Was going to start ordering caps, but have a question.  Any reason to not use ceramic caps to replace electrolytic caps, if value, and voltage ratings are equivalent?  I'm thinking they will last much longer, and have more stability.  It seems that most signs say yes, but low ESR of MLCCs might cause issues, but not sure if this in this case would be any concern.  I also may already have them on hand.  Anyone done this?

you'll spend a fortune trying to find ceramic or non-electrolytic caps at the size/ratings you need for the 1702. just order the kit from console5.com and recap the beast. they will last another 40 years, which, depending how old you are, won't matter as you won't be around to recap it again.

[wildstar87]

I understand, but I have a lot of these values in ceramic caps already, not saying I will replace all with ceramic, since some values aren't even available.  Cost wise it's saving me money, but that wasn't the primary question, functionally I can't see a reason not to do this, but if someone knows a reason why not, would like to know why?  I'm also looking at some of the values in the service manual, and I can't find equivalents for the values/voltages AND tolerance specified, and the cap packs from console5 and others don't list to tolerances of the caps they use.  I suspect where -10%/+30% is specified, they might be using 20%, as 10% is not really available for some values, in electrolytic.

 

Also, the service manual doesn't seem to actually list all the electrolytic that are on the board, the list seems incomplete, but the list on console5 wiki has a lot of caps listed that don't have a corresponding value in the service manual, other than trying to track down each value in the schematic.

 

Yes, I realize that I'm probably making this more difficult than it needs to be, however that doesn't stop my mind from asking the questions, and as the answers don't seem readily available, thought someone else might have them. 

[_The Doctor__]

please consider why different caps are used in different applications

[Level42]

On 10/2/2021 at 10:28 AM, wildstar87 said:

Got around to pulling this all apart today.  Was going to start ordering caps, but have a question.  Any reason to not use ceramic caps to replace electrolytic caps, if value, and voltage ratings are equivalent?  I'm thinking they will last much longer, and have more stability.  It seems that most signs say yes, but low ESR of MLCCs might cause issues, but not sure if this in this case would be any concern.  I also may already have them on hand.  Anyone done this?

I never go with cap-kits because of the following reasons:

- usually they provide generic, unknown brand caps. I want the best, so Panasonic or Nichicon or Rubycon and nothing else.

-usually they provide 85 degrees versions, I go for 105 degree ones

- usually they lack one or two caps that ARE on your typical version of the device. Remember that factories made many revisions, and by what you write it seems you already have more or different valued caps.

-sometimes values don’t match, not talking about tolerances, those are not very important really. Voltage isn’t a problem either as long as it’s higher than the original.

In most cases, but definitely not all, it is also OK if the capacitance is a bit over the specced value. This depends on the application in the circuit though.

 

so, usually I simply write a list of all the caps that are on the device I have on the bench and select them from f.I, RS online or other trustworthy electronics online companies. You will probably have minimum numbers for smaller caps, but even so, it’s usually not (much)more expensive then getting a kit, plus you will have extras for other jobs.

 

And forget the thought of replacing electrolytic with ceramics, you will need physicaly huge ceramic caps compared to electrolytic ones. There is a reason why electrolytic caps were developed: very high capacitance in a small space. 
another reason not to do it is because no-one who has a bit of expertise with electronics repairs does it.

there must be a reason…

 

 

 

Edited October 3, 2021 by Level42