IBM 5154 problems

[robbo007]

Hi guys.
I've got issues with my IBM 5154. I was having sync issues when in 21.85khz mode. I could not get a clear picture so I turned the RT301 (vertical frequency control) and it fried the power supply. I fixed the power supply then had a horizontal white line across the screen. So I tried the RT301 again and once again fried my power supply.

Any ideas what is causing this or how to troubleshoot? I'm no expert but can learn quickly.

I guess there is some power deviation but what I dont understand is why when turning the RT301 my power supply gets fried. There was an issue before with the vertical sync circuit as I could not get a clear picture in 21.85khz mode. 15.7khz worked fine until I fried the power-supply.
Thanks,

 

[modem7]

I fixed the power supply then had a horizontal white line across the screen.

"Vertical collapse."

Any ideas what is causing this or how to troubleshoot? I'm no expert but can learn quickly.

1. For a start, we know that this cannot be due to a lack of vertical sync pulses, because without the IBM 5154 connected to a working EGA card, the vertical stage in the 5154 'free-runs', per the photo at [here].

2. See the 'Full or partial vertical collapse' section of [here]. You could take a punt and replace the TDA2653A, but know that others tried that, and the problem turned out to be something else.

3. Do you own an oscilloscope ?

4. If you haven't already, turn the brightness down, to reduce the possibility of 'screen burn'.

 

[robbo007]

Thanks. No oscilloscope. I’ll take a look at the TDA2653A. Any ideas what could be causing the power supply to blow when moving the vertical frequency dial?

 

[modem7]

Any ideas what could be causing the power supply to blow when moving the vertical frequency dial?

No. For now, I suggest that you put the potentiometer ('pot') into its midway setting and leave it in that position for now. Later, when you restore vertical deflection, then adjust it per the instructions in the Sams Computerfacts document for the IBM 5154.

By the way. In case you are unaware, be aware of the safety information at [here].

No oscilloscope.

Depending on the problem cause, you may be able to get by without one.

I have taken a look at the circuit diagram. The portion for vertical deflection is shown at [here]. The core is a TDA2653A chip. A 4053 chip is being used to select which 'vertical size' potentiometer is used (one for 'CGA' mode and one for 'EGA' mode).

The first thing that you should do is verify that the power supply is generating +21V and +12V. Pin 9 of the TDA2653A is the ideal location to measure the +21V (i.e. 21V is actually reaching the chip).

( +21V is what the Sams people measured. I am sure that a certain voltage variation is tolerable. )

 

[modem7]

An interesting experiment:

The 5154 monitor is in effect, both a CGA and an EGA monitor. The 5154 monitor switches between CGA mode and EGA mode depending on the polarity of the incoming vertical sync pulses. These two modes are described as modes 1 and 2 at [here].

So, the experiment would be to try your 5154 in both modes. If you get vertical deflection in one of the modes, ruled out is a lot of the vertical deflection circuitry.

I think the easiest way to try CGA mode would be to connect the 5154 up to an operating CGA card.

( A way to see/confirm which mode your 5154 is in, is to measure pin 4 of the ROM designated IC502, per the diagram at [here]. HIGH for EGA mode. LOW for CGA mode. )

 

[andy]

"Fired" isn't very specific. Exactly what keeps failing in the power supply?

Both modes run at the same vertical frequency, so if it works in CGA, it should also work in EGA. There's no good reason adjusting the vertical hold should damage the power supply.

How heavily used does the monitor look? Has it been recapped?

 

[robbo007]

Thanks for the replies. I'll gather the info as I need to open the PSU again and see what is actually "fired" I had it in a shop that in the end fixed the PSU but did what I did to adjust the vertical sync then it blew the PSU again and they gave up.

I did a complete recap myself. I took time and checked all caps 4 times. To make sure they were right ones and polarity was correct. I used very good quality caps and high temp rating. After recap, the monitor looked amazing. Then I started to get some blue tones on screen. Then I tried the 21.85khz mode and I could not get a stable picture so I tuned the vertical sync RT301 knob and then blew PSU. The shop had it for a while but did not really want to fix it. They resovled PSU problem and then I think changed the TDA2653A chip with one they had lying around.

I will try and open this weekend and take a look and report back.
Thanks, I really appreciate the help. Took me years to find one of these.

 

[andy]

For what it's worth, I can't see any way that adjusting RT301 could take out the power supply. Assuming you didn't slip with the screwdriver, and short something out, the only possibility I can think of is that RT301 is noisy, and caused the vertical amp to momentarily draw excessive power. At worst, that might have caused the power supply to shut down, or opened a fusible resistor.

I recently worked on a 5175, which is similar, and some of the pots were very noisy, and required cleaning, or replacement. The vertical frequency was one of the problematic ones, which initially caused no vertical deflection. It didn't cause any other damage though.

What makes you say the power supply was damaged? Was there smoke? Is it totally dead now?

I'd offer to repair it for you, but international shipping would be expensive.

 

[robbo007]

Exactly. It does not make sense the RT301 would blow something on the PSU. I definitely did not touch metal with screwdriver. I used a plastic one as I was worried of getting electrocuted. haha

I will open the psu this weekend and try to find the fault. Right now I’ve got no power when switching on. I do hope it’s something simple like a fuse. I will check power lines as mentioned above and report back my findings. Thanks

 

[robbo007]

Hi guys. I'm back on this project. I recently acquired an AS/400 mid-range and was trying to get my head around all the tech and OS400. A mission. lol .
So I was looking at the power supply and nothing visual seems damaged. So I checked fuse, all good, I checked out output voltages and bad. Nothing reaching output nor the IC2 12V. So I checked the MJE13005 transistors at T5 and T6. T6 seems fired. I'm not getting any readings. T5 seems ok. I've ordered replacements. I also checked all resistors and diodes and they seem fine. I'll report back in once I've replaced T6 and see if I get any closer to getting a working PSU.