Texas Instruments TI-99/4a Argentine (Spanish) Version Repair.

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 9900NL CPU (U600)
• 1 x Burned Resistor (15 Ohm)

Note: This motherboard has already been repaired by someone at least once.

Gallery of the repair:

This is a very old article from 2016 that i never published on my blog.

Summarizes the purchase, shipping, cleaning and simple repair of a Commodore 4064 with a very low serial number.

Since i had not talked about the repair, i begin to tell that only the VIC-II 6569 Video Chip in Ceramic format was broken.

In the photos there is also a comparison between the Commodore 4064 (PAL) and the Commodore Educator 64 (NTSC)

Below the old article.

The title of this post is: I want it at all costs.

But what? a computer! which model? an old one that I missed to complete a part of my collection.

This computer is really unusable, as are all of them, but this one beats them all.

It’s a Commodore 64 in a PET case produced in 1982, with a green phosphor monitor, stripped of the sound chip (SID 6581) and colour RAM (2114), with a modified kernel that doesn’t use any colour, and a keyboard with different 1..8 keycaps (no colour code on the front).

What’s left? An useless computer with no sound and no green-scale colours; it just uses black and green, while the Commodore Educator 64 has sound and can show colours in shades of green.

After getting the Educator 64 I wanted to complete the pair with a Commodore 4064, and I started to look for it.

I saw a few 4064s that sold for bizarre prices – I can’t say that they were high, because if you want something you are willing to buy it whatever the price, but anyway…

Here begins my adventure :-D

At one time a 4064 pops up in a well known auction site – take note that I don’t use artificial intelligence search engines to look for items, I don’t give a shit… if I find something when I look for it, that’s fine, otherwise it’s not a big deal.

That one was located in Germany, the price was low (at least for me – someone considered it very high), but was the seller willing ship? No he wasn’t.

I wrote to him, no reply, I sent the same message translated in German (thanks google), he responded in German telling me that the item was too big and he didn’t know how to deal with it.

I wrote him again in google German, telling him that I could send him some shipping and packaging instructions – I have them ready in many languages. His reply: I don’t ship.

I was sad and discouraged, because even if the unit wasn’t working, it was in an excellent aesthetic condition and with no missing parts.

I asked for help to my friend Andrea, who asked Ciro, who told me that I could ask his German contact Ralf Schmitz if he could lend me a hand.

Meanwhile the auction was getting near the end… still at a low price.

I wrote to Ralf – a very kind person – and he explained to me that he lives 530Km far from the place where the computer was located. Things got complicated.

I asked Ralf to contact the seller, who maybe preferred to talk with a compatriot :-D

The seller didn’t reply, the auction was ending, what should I have done? I love to risk, and while in chat with Ralf I told him the maximum amount to bid.

I won the item at the right price, in the right moment.

Then what? The seller didn’t have many feedbacks but Ralf suggested to pay right away with Paypal which offers buyer’s protection without the risk of losing the money.

I sent the money to Ralf with Paypal, and he paid the seller.

Ralf wrote him. No reply. The Easter weekend went by, still no reply.

And then one day… the guy replied! Ralf could contact him by phone and they chatted for more than one hour. The man seemed good; old but fair.

The seller told Ralf that he didn’t want to ship because he didn’t know how to properly package, he didn’t have packaging material and he didn’t want to look for it… then he told that he should have to buy some tape, and petrol for the post office, and so on…

I talked with Ralf, and one of the ideas we ditched was to ask someone to go to the seller’s place to help him to pack the 4064 and have it sent to Ralf with some kind of hitch-hiking.

I was suffering.

New solution: simplify the shipping.

I explained Ralf how to separate the monitor from the base: it’s a matter of unscrewing 5 screws, detaching a connector from the motherboard, and cutting two wires (I didn’t even think about explaining how to unsolder them).

The seller was was fine with the idea.

Ralf had to send a huge package containing the packaging material – boxes, foam and bubblewrap – and written instructions from me and Ralf.

The seller shipped the packages with DHL, which in Italy delivers using SDA (one of the cheapest and lower quality couriers). Panic.

The seller is old so he shipped one box at a time: the monitor first, that arrived in 5 days, then the base, that took much longer and made my anxiety skyrocket – Ralf told me that DHL had a few problems in Germany but the package should have crossed the border.

While he was writing to me, the second package arrived at destination.

The computer is now complete and in excellent condition, and with a slightly low serial number :-D

My thanks to Ralf Schmitz because without him this wouldn’t have been possible, and to Andrea for putting up with my anxiety during the last 20 days.

And my thanks to Giacomo Vernoni for translating this report, otherwise I would have written just a paragraph of text – and that would have been a pity :-D

Gallery:

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First of all, a premise: All the repairs i do are for hobby purpose ONLY. It is NOT a job, and i fix stuff for a selected people group that i consider needs my help. All other people please ask somewhere else to get your items repaired back.

A guy contacted me 3+ months ago (April 2019) asking help to fix his Amiga 4000D (Yellow screen at boot for a couple of seconds, and then black). I agreeded to help him.

This Amiga 4000 was tested with A3640 and a Phase5 Cyberstorm MK3 CPU cards, with which the A4000 does not work with the same issue descripted above.

I immediately noticed a fairly important damage caused by battery and caps acid leakage (especially in the audio area, see photo).

After cleaned everything, i rebuild some interrupted pcb tracks on the motherboard (audio / ram / status led section) and replaced capacitors on both motherboard and 3640 (the fault persisted, of course).

Next, i used the Chucky DIAGROM: the DIAGROM is useful to understand what might be that doesn’t work, and the output via RS232 is also very useful if nothing is displayed on the screen.

DIAGROM reported some issue with all IRQs and CIA Timings, but everything else was working (video output, images, sound, mouse, joystick ..ect..).

The IRQ problem is well known in the Amiga 4000 repair circle, because it could be caused by IRQ _CIPL or _IPL interrupted lines, the pcb tracks start from PAULA and goes to the GAL U701, and from the GAL to the CPU connector.

Well, I checked all the IRQ lines, and they were good. I checked again, everything was ok (the checks must be done from PAULA to the GAL and from the GAL to the CPU connector, amiga pcb solder side and CPU card pcb solder side) at this point i thought that GAL U701 was dead, so i programmed a new GAL and replaced it. Unfortunately nothing changed.

Thinking about what it would cause the GAL not working properly, i pointed the finger to the GAL CLOCK, exactly to the pin 1 of the GAL U701.

The Clock was there but something was not clear to me: the signal i see on the oscilloscope was corrupt, fixed at 5V. At this point i said to myself, what is that supplies clock signal to the GAL? Clock on the pin 1 of GAL U701 is supplied by the IC 74F86 U711, pin 6, via the resistor R702 (obviously resistor was good).

I called my friend Andrea (Andry) and asking him to check on his A4000 the value of that pin (6) of the IC U711 (i could have done that myself on my Amiga 4000, but disassemble it’s a nightmare). My friend does not have an oscilloscope, so i asked him to check the power using a digital or analogue DC tester. On his A4000 the value of U711 pin 6 was was completely different than my value.

Bingo, it is! i run to the local electronics store to buy a SMD 74F86 IC, but obviously they didn’t have it.. so, i purchased it on Ebay, replaced it, and yes, it was dead.

It was not the only faulty component, because replacing the new GAL U701 with the original GAL U701 did not work. So, the original GAL was dead, too.

New IC U711, new GAL U701 and the A4000 is back to life.

Other minor fixes i have been done on this Amiga 4000 are: useless replacement of an 8520 (U300), installation of cooling fan on the CPU 68060 – 50MHZ on Cyberstorm MK3, rebuild of a broken resistor damaged by the caps leak.

No more other to say, except that i am happy i succeeded to repaired this Amiga 4000 for a person that needed my help.

Gallery of the repair:

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Video:

I will never stop repeating; please you must repleace all capacitors of the newbrain before turning it on.

I have replaced all capacitors some with acid leaks and this time everything has worked very well.

I left the computer running for a couple of hours and no other problems have been manifest yet … but it won’t last forever.

Gallery of the repair:

Useful link to visit: 8bit-homecomputermuseum.at

The first thing to do with this home computer before turning it on after many years that it was off is replacing all capacitors, which i did (some capacitors with acid leaks) and the computer worked well for about 15 minutes.

After the first 15 minutes while running a “for next” cycle, the computer started to show signs of slowing down and then freezed.

The problem was a RAM (4116) on BANK 2 [POSITION 416] (see photo), replaced the RAM the computer has started working again for another 15 minutes then it was freezed again.

I turned it off and on again and in this time a single line was repeated for X times, only with the composite video output, the VFD Display worked well (see photo)

Looking at the wiring diagram i found the area that manages the composite video output and i started to making measurements with the oscilloscope and after quite some time i have found the IC 74LS157 [POSITION 449] with a strange measurements that did not convince me for example the output pin 7 (OUTPUT Y2), in fact was broken, replaced the component the computer has started to work again.

Hopefully nothing will happen again: D

Gallery of the repair:

Useful link to visit: 8bit-homecomputermuseum.at

This is the Battery Pack for the Newbrain, very comfortable and very light :-D useful for taking the computer to the beach during the summer holidays.

Obviously the Battery Expansion Unit after many years of inactivity has presented some problems of the 20 x 1.2V 600mA NiCd batteries.

The batteries besides being completely exhausted i had leaked acid. (see photo)

Fortunately, there are no major damages with the leakage of acid and it was enough to clean well, unsolder the 20 batteries and replace them with new ones of 1000mA.

Last update: I noticed a malfunction of the Battery Expansion Unit, when i set the switch to OFF the “discharge” LED remained on.

Looking at the schematic, the switch suspend the charge and the use of batteries, the problem was caused by a pcb pad (see photo) that at first sight seemed to be connected together with another, immediately close, but in truth it was not so, it was enough isolate the connection and now everything works correctly.

Gallery:

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I have removed the blown filter capacitor of both PSU and cleaned the dirty cables.

Gallery:

Commodore A501 (REV 6C) Expansion Memory Unit Kissed by luck.

Why “lucky”? because the battery used in this Expansion Ram Unit (A501) was not VARTA but GP, these batteries resist slightly to aging and release less acid.

Gallery:

Atari 2600 (4-switch units) Repair.

Defect:

• Black Screen.

Replaced parts:

• 1 x CPU 6507 (A200)

Gallery of the repair:

SNK Neo Geo MV1a Z-80 Error Repair.

Defect:

• No Sound (Z-80 Error)

Repair:

• Replacement of the Z-80 CPU in PSOP40 format.

Note:

• The error message “Z-80 Error” means everything and nothing, may be faulty the Z-80, SNK MASK-ROM SM1*, SNK NEO-D0 or also the YAMAHA YM2610.

With the Neo Diagnostics bios and with the M1 ROM burned and installed on the CHA Board of any NEO GEO cartridge, the problem can be better identified.

It is said that the error C3/00 that you see in the photos of NEO DIAGNOSTICS (write: C3 but reads: 00) is an almost assured a CPU problem, in fact, in this case it was.

The Z-80 CPU in PSOP40 format has been recovered from a failed SEGA GameGear.

Gallery:

source: neogeo diag

Texas Instruments TI-99/4A Repair (1 of 2)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 4732/2532 ROM (U611)

Gallery of the repair:

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Texas Instruments TI-99/4A Repair (2 of 2)

Defect:

• Garbage Screen.

Replaced parts:

• 1 x TMS4116-20 RAM (U103).

Gallery of the repair:

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Download: TI99 Technical Manual (831)

This Commodore Amiga 600 is arrived in laboratory in immaculate state still with the warranty sticker.

Immediately after the disassembly i have immediately noticed that were are several problems of acid released from the capacitors and dirty that affected this poor Amiga 600 and its Floppy Drive.

A decoupling capacitor it’s exploded with a pit on the PCB side, solved this problem i started to replace all the electrolytic capacitors and to clean the pcb with specific products.

After the replacement of the electrolytic capacitors, i have tried to turn on the amiga that apparently worked, shame about the distorted sound and the floppy drive that read 1 time of 100.

I had to replace the electrolyte capacitor on the Floppy Drive and soon after i looked for the fault of the audio problem that 99% is always the usual LF374.

In this case it was not only LF374 but also a 10ohm resistor that did not let the +12v to the LF374 and a short-circuited ceramic decoupling capacitor.

Components that have been replaced:

• IC LF374 substituted with a fully compatible TL084C (U15)
• 10Ohm resistor (R301)
• 330nF capacitor (C301)
• 330nF capacitor (C41)

Unfortunately the welding of the LF374 did not come very well how i like to do it but the pad are destroyed and corroded by the acid and they were about to detach, indeed the pad of the pin 2 of the LF374 was really detached, that’s why the pin 1 and 2 of the IC LF374 are connected together, they were connected via the pad.

I leave you to the photos and the video.

Gallery:

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Video:

The Commodore-SX64 keyboard after some time isnt’t responding anymore (all or some keys). In this case, the keyboard needs some cleaning and repair.

First of all you have to disassembly the keyboard housing, pay particular attention to the screws, this plastic is very old and not of a good quality, it breaks only if you look it.

Gently remove the membrane and clean with alcohol all the metal contacts on the keyboard pcb and also clean all the contact pads on the membrane without alcohol.

Next i took some graphite in cream (Keypad Fix) to reconstruct the pads on the membrane by simply applying a very fine layer of graphite on the contacts.

Gallery:

This monitor although fully functional in the video section, was missing audio. The integrated circuit of amplifying sound (TDA 2611A) was not powered.

The problem was a broken pcb track (see photo), solved this problem the sound is back.

Gallery:

I received this small Black and White CRT monitor from a friend, Ciro Barile of TI-99 Italian User Club, this monitor was used as a video intercom and i didn’t know the power supply voltage, the pinout but especially if it worked.

Found the pinout and the power supply voltage i saw the image turned upside down, this because the monitor could be hooked both from top and from bottom, nothing could be easier it was enough to change the deflection yoke connector on the motherboard to flip the image.

I drilled two holes on the back of the case to facilitate access to the composite video input and power supply (12v 2A).

Pinout:

• RED (Video)
• GREEN (Ground)
• BLACK (Positive)
• BROWN (Ground)

Gallery: