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this 5155 screen, easily fixable?

S

shine

Member
Joined
Feb 10, 2020
Messages
21
Location
Between Barcelona and Bilbao, Spain
Hi,

I'm in the mood of buying a 5155 portable, i found one at a fair price but the owner showed me that the CRT is broken.

I think it may be the power supply, the p12 connector I read in another thread. What are your thoughts?

Would you pull the trigger and buy it at 250€ price? It comes as-is, no disks and no manuals.

Image of the screen:

d7e9e72a076f18e38a6966909ad8ee2bo.jpg


Thanks!!
 
Seems like the CRT is fine, but something else is wrong. The CRT looks normal for when you have the brightness and contrast turned up all the way
 
shine said:
I think it may be the power supply, the p12 connector I read in another thread. What are your thoughts?
Click to expand...
The P12 connector (supplies +12V to the display) problem that has arisen at least twice, results in the 5155 booting, text seen on the display, but the text is 'jumping up and down slightly'.
 
Does the 5155 appear to be starting?
So, about a minute after power-on, the floppy drive LED is expected to turn on for a little while (as the motherboard's power-on self test checks the drive).
 
If the computer boots up, it could be the connector from the screen to the CGA board is loose or not connected.
 
shine said:
Would you pull the trigger and buy it at 250€ price?
Click to expand...
You are asking the question of something that needs to be repaired. I can repair these things myself down to component level, and so the cost to me would be about 250€ (plus my time). We can provide some diagnostic guidance, etc. to you, but in the end, we may be telling you that you need a new motherboard (for example), and so the true cost of the 5155 to you (or others) could be say, 350€, or more.

shine said:
What are your thoughts?
Click to expand...
Based only on the symptom shown by the photo, some single-failure possibilities that I can think of:

If the motherboard's power-on self test (POST) is observed to be checking the A: drive:

* Video cable has fallen off the IBM CGA card.
* Faulty IBM CGA card.
* Faulty display unit.

If the motherboard's POST is not observed to be checking the A: drive:

* Power supply problem (faulty, but at least +12V being supplied).

* Motherboard problem - Socketed chips need to be re-seated.
* Motherboard problem - Faulty RAM in first bank.
* Motherboard problem - Short circuit tantalum capacitor. <------ Common
* Motherboard problem - Corrupted ROM chips.
* Motherboard problem - Other.

* Expansion card problem - Faulty in a way that overloads power supply (e.g. short circuit tantalum capacitor).
* Expansion card problem - Faulty in a way that interferes with address/data bus operation.
 
Your moderated posts have appeared.

shine said:
Yes it boots, the floppy disk light turns on.
Click to expand...
And expected as well, would be a single beep from the speaker, at roughly the same time as the LED turns on.

Revisiting some of possibilities that I listed in my previous post:


Video cable has fallen off the IBM CGA card
--------------------------------------------

Photo at [here].


Faulty IBM CGA card
--------------------

Assumption: Motherboard good, and motherboard's video switches set for CGA.

Card substitution would be the quickest way to test that.

There is only one socketed chip on the IBM CGA card. It would be worth re-seating that chip.

Connecting a CGA monitor to the IBM CGA card's DB connector, or connecting an NTSC composite monitor (or NTSC compatible TV) to the card's RCA connector, would be revealing.

If required, a replacement CGA card does not need to be an IBM one. There are some CGA cards that have the required connector.


Faulty display unit
--------------------

We know that the display unit is getting +12V.

Diagnosis would require the use of an oscilloscope.
 
My "Assumption: Motherboard good, and motherboard's video switches set for CGA." in the previous post, raises two other possibilities:


Motherboard's video switches set incorrectly
---------------------------------------------

Need to be set for CGA.
If incorrectly set for MDA, an error beep pattern of '1 long beep then 2 short beeps' would be heard from the speaker very shortly after the 5155 is powered on.
If incorrectly set for EGA, no error beep pattern will be heard.

Confirm correct switch settings.


Faulty motherboard
-------------------------------------------

The motherboard's video switches could be set to CGA, but faulty/dirty switches, or faulty switch support circuitry, result in the POST believing that the switches are set for MDA or EGA.

If set to CGA, and the POST believes that EGA is set, then even with no display to work from, it should be possible to prove the scenario. Without a boot disk, the 5155 will jump to Cassette BASIC. Even though one cannot see the screen, certain BASIC statements can be entered, to first prove that BASIC is running (by entering a BASIC statement that beeps the speaker), and then to enter conditional statements that interrogate the switches and beep the speaker if True.
 
shine said:
Thank your for all your insights, I have to speak with the owner and reduce the price, otherwise I won't buy it.

Thanks!
Click to expand...

At 270+ USD, guess not including shipping unless it's local, I would not buy it as-is. There are often good working 5155 popping up on ebay for less than 150 USD, which makes more sense to me.
 
The ones popping up for less than $150 are all not working. The ones tested working are around $250 US. (This is based on the last 10 ebay sold listings done from a search just now.)
 
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