Fixing an 88-PPG 1702A Programmer

[Grant Stockly]

I borrowed a MITS 88-PPG 1702A programmer from H. E. Robert in December. I did not get around to trying the programmer for some time and when I did it did not work.

Not only did I have a need to program/copy 1702A EPROMs, but I can't return a borrowed item broken! At the time I was not sure if it had arrived to me broken, or if I did something to it! I later found the issue, a solder joint, and there is no way *I* did it.

I detailed the problem and process that I went through to fix it on the "Altair Computer Club" yahoo mailing list run by Steve Sheppard, a former MITS employee.

I talk about files during the process. All those files are available here:
http://www.stockly.com/images3/MITS_88-PPG_Debug/

Data sheets, logic analyzer captures, pictures, etc...

[Grant Stockly]

From: Grant Stockly
Date: Sat, 02 Jun 2007 03:43:51 -0800
Subject: [Altair Computer Club] 88-PPG Troubleshooting


NOTE:
I JUST programmed a EPROM to find out if letting the thing sit powered up
would do any thing. Well, I now have a perfectly programmed PROM. I
seriously doubt the problem is with my 88-PMC, because it is brand new and
the programming program is running off of it. If the source data were
corrupted from a bad PMC then the program would just crash.

I did replace a CS4410 in the programmer responsible for the programming
pulse, but I think it was working before I replaced it.

I'll find out in the morning if when cold it still does the same thing. It
had a while to warm up because I had to trace out all 18 signals, then
write all this junk, then I programmed a PROM. Probably a good 3
hours. Grrr.... I wish I knew if it was fixed for good. : ) At least
the logic analyzer is hooked up to it and ready to go. In the morning I'll
see how it behaves. : )

The last file I uploaded to the altaircomputerclub I set the "notify group"
button. I thought it might provide a link to the files section for those
who don't know how to get there. Make sure you find all of the stuff! : )

3AM and this programmer testing is testing ME. : ( Now for the message
that I didn't want to let go to waste...

===

I borrowed a MITS 88-PPG 1702A PROM programmer and can't seem to make it
work right. I've programmed about 8 EPROMs. My success rate is 30-60% PER
EPROM. I have never been able to get one good EPROM yet. I will be
uploading some software and data files to the user area for anyone
interested. I'd like any input I can get. : )

I have a DigiView USB logic analyzer. It is a GREAT tool. I located TTL
versions of A0-7, D0-7, Program pulse, and the VGG-VDD power pulse. I
attached those 18 points to the analyzer with little clip on probes and
took ground off of an '04. The address is normal, but the data byte is
inverted. Using the software I've uploaded (its free) you can search the
activity of the programmer on all 18 connections with 10ns resolution over
177 seconds. Did I mention I love this thing? : )

First I'm checking the timing tolerances.
tACW is the Address Complement Set-Up. These 1702s require the desired
EPROM address to be supplied in an inverted state before programming power
is applied. Once the power is supplied and tACH Address Complement Hold
expires the real address comes in. Finally there is a programming
pulse. Seems overkill, but I'm going to check every single possible point
for failure. : )

tACW Address Complement Setup: Minimum of 25us, is actually 286us (wow?!?)
tACH Address Complement Hold: Minimum 25us, is actually 292us
That is where things look weird. At the end of tACH the program pulse is
supposed to go negative, but it doesn't go negative for another
287us! Maybe this is the problem?
tVD VDD VGG Hold: Min 10us Max 100us, measured 65us - Looks Good
tVW VDD VGG Setup: Min 100us, measured 580us
tDH Data Hold Time: Min 10us, measured 172us
tATW Address True Setup: Min 10us, measured 287us
tATH Address True Hold: Min 10us, measured 201us
tDW Data Setup Time: Min 25us, measured 826us
tPW Program Pulse Width: Avg 3ms, measured 2.839ms

I don't know what to think now. I thought that the tACH could be where
things went wrong, but tATW looks like its within spec... Maybe I should
focus on programming voltages and figure out what timer controls the
programming pulse? My problem isn't enough time to program a 1, its that
extra 1s seem to be getting into the EPROM!

Some random info...
From the falling edge of the first power pulse to the rising edge of the
last power pulse for one 256 byte programming cycle I measure 7.17
seconds. With a programming pulse being 2.8-3.4ms on average we have a
good 10% duty cycle, well under the 20% duty cycle maximum.

Where is my problem! : ( What I need to do is hook the logic analyzer
directly to the EPROM socket. There are 128 resistors and 32 transistors
after the points where I was sampling. Still, I got extra bits programmed...

[Grant Stockly]

From: Grant Stockly
Date: Sat, 02 Jun 2007 13:42:24 -0800
Subject: Re: [Altair Computer Club] 88-PPG Troubleshooting

This morning I tried to use the programmer "cold" and it failed. At least
its not "me". The problem is for sure in the programmer or interface
card. The symptom of only programming every other byte and not programming
the bytes that it did do correctly is reflected in the logic analyzer
reading. I have uploaded two more files. One is a picture of the problem
and the other is a 170 second log of what happened on the programmer.

A noticed that quite a few of the ICs legs are tarnished. Some are almost
black. This must have been from an incompatible IC and socket combo. What
is the best way to clean these ICs? Its possible that as things heat up
the legs scrape a little and get better contact? Even if the ICs are
cleaned, a tarnished IC must mean that the socket is bad too, right?

I have a Altair 680 Ram card from Tom that has golden pin ram chips. All
of the chips have pins that are literally cracking off. I would think that
this is because of some anode/cathode thing going on. Its not the gold,
but the steel or what ever the legs are made of. Some crack off and some
even break off when the chips are removed from the sockets. The other ram
card I hvae of his has non gold plated pin 4200 chips and they are all
fine. Same sockets.

Tarnished sockets and pins is something we have to look out for in these
old computers...???

Grant

[Grant Stockly]

From: "Steve"
Date: Sun, 03 Jun 2007 04:17:32 -0000
Subject: Re: [Altair Computer Club] 88-PPG Troubleshooting

It's probably not the sockets. The old conductive antistatic foam
that they used to store chips on reacted badly with the pins, and
gold ones usually came out the worst, sometimes looking like they had
been eaten away by acid (isn't gold supposed to be relatively inert?
Not in this case). I have lots of chips in that condition. Silver
pins came out better, but were still susceptible. The "oxide" (or
whatever it is. Sulfide?) can be removed with a coarse eraser. I
made a little fixture that would prevent the pins from getting bent
as I scrubbed. MITS used lots of that "reactive" foam.

Usually, working the pins in and out of the socket several times will
scrape through the insulating coating. ZIF sockets are a different
matter, since they don't usually scrape the pins at all during
insertion. A trick I use with ZIFs is to partially squeeze the
chip's pins by partially closing the clamping lever. This grips the
chip, but loosely enough that I can still slide the chip left and
right in the socket a few times, causing the pins to be scraped off
for better contact. I ALWAYS do this when I blast old EPROMs, even
if they look OK.

It's tough to solder to such pins, too.

Some day, I'll buy a bottle of Tarn-X tarnish remover and give it a
try.

Steve
=============================
--- In altaircomputerclub@yahoogroups.com, Grant Stockly <grant@...>
wrote:
...
>
> A noticed that quite a few of the ICs legs are tarnished. Some are
almost
> black. This must have been from an incompatible IC and socket
combo. What
> is the best way to clean these ICs? Its possible that as things
heat up
> the legs scrape a little and get better contact? Even if the ICs
are
> cleaned, a tarnished IC must mean that the socket is bad too, right?
>
> I have a Altair 680 Ram card from Tom that has golden pin ram
chips. All
> of the chips have pins that are literally cracking off. I would
think that
> this is because of some anode/cathode thing going on. Its not the
gold,
> but the steel or what ever the legs are made of. Some crack off and some
> even break off when the chips are removed from the sockets. The other ram
> card I hvae of his has non gold plated pin 4200 chips and they are all
> fine. Same sockets.
>
> Tarnished sockets and pins is something we have to look out for in
these
> old computers...???
>
> Grant

[Grant Stockly]

From: Grant Stockly
Date: Sat, 02 Jun 2007 20:41:05 -0800
Subject: [Altair Computer Club] 88-PPG fixed with story


Using the data from the logic analyzer I traced out the problem with the
88-PPG and fixed it. This makes me happy and I'm sure Robert too. :
) Btw Robert if you are reading this please call or e-mail me! : )

I've uploaded all data sheets for the ICs listed and a ton more stuf in the
file area. All you digital pack rats should go take a look at it. : )

There is also a picture of a 88-PMC ROM card with a ZIF socket
installed. This allows me to swap ICs without removing the card.

===

A0 is stuck high. This causes no odd bytes to be programmed and all even
bytes to be programmed twice with data from the associated odd byte. : (

There is a section on the motherboard where A0 is buffered twice. The
input to the circuit is 0-5v TTL and the output is -48-0v. A0 is stuck
high before this. A0 is generated by a 7400 positive NAND gate, 4Y (pin
11). Pin 13 is high. Pin 12 needs to be high in order to make pin 11
low. Pin 12 goes to a 8212, an 8 bit I/O port, pin 4 where it is stuck low.

Pin 4 on the 8212 is DO1 (data out bit 1 of 8). Pin 3 is the associated
DI1 (data in bit 1 of 8).

There is no activity on pin 3 of the 8212. The 8212 is not bad.

Pin 3, DI1, is shared on all 3 of the 8212s. If it is stuck low then D0
should be stuck low too. I checked the wave form and D0 NEVER goes
high. Hmmm... : ) A0 stuck high, D0 stuck low. This makes sense since
the data lines are inverted compared to the data.

Pin 3 on the 8212 goes to pin 2 of a 74LS14 a Hex Schmitt-Trigger
Inverter. Pin 2 is an output, pin 1 is its input. This is one of the
tarnished ICs... Nothing at all on pin 1.

Pin 1 on the 74LS14 connects to R11, R12, and pin 9 on the system interface
cable. No signal there either. There is no signal on pin 9 of the S-100
interface card either.

The problem is in the interface card. Its pretty simple. : )

Pin 9 on the interface cable goes to:
-pin 24 on an unidentified empty socket.
-pin 3 of IC D, a 74367 a Hex Buffer Driver with tri state output
-pin 6 of IC G, a 8836 (quad NOR gate, sorry no data sheet)

The 8836 pin is an input, so unless it is shorting then it isn't the
problem (I have seen this...).

The legs on IC D are tarnished a nice dark black color. : ) Pin 3 is an
output, pin 2 is the input to that buffer. Pin 3 on the IC socket was not
soldered very well at all. Looked like someone blew their nose on
it. This is weird because the rest of the board is nice and shiny. When
it heated up it must have pulled tight against the board. I noticed that
the when sticking a wire into the socket it had no resistance and when
pulling it out it varied between 200 and 5 ohms. : )

It works now! : ) I just copied the PPD ROM and used it to make copies of
other ROMs. : )

Grant

[Grant Stockly]

From: Dan
Date: Sun, 03 Jun 2007 01:03:30 -0400
Subject: Re: [Altair Computer Club] 88-PPG Troubleshooting

Tarnish has been a common problem for a long time. I use see boards that
we made only a few years after the design was released(early 80's) begin
to suffer the tarnish syndrome. It's mainly due to the silver alloy used
on the old TTL/CMOS chippys which underwent severe oxidation (the
blackness of hell)--humidity is also a factor which leads to this. Some
chips that don't suffer from this contain a different alloy plating,
possibly tin. The gold isn't 24k--the purest-- probably either 14k or
16k, which can wear off from the oxidation (on the microscopic level).
The broken legs are the result when the pins are bent at the factory to
create the DIP style package. The bends contain micro fractures which
allows the oxidation to creep in, causing a chemical reaction between
the three--plating, core material,oxide. This causes the fractures to
expand even more, further weakening the tension of the leg and
eventually crack/fall off. The sockets can also be a victim from this.
I've had to replace many sockets too. One method I use --which kills 2
birds with one stone-- is to use a fine grit sandpaper(120grit) to clean
the legs. Then if any of the legs have lost their tension, they'll show
up immediately wherever it's cracked. I've had to resolder many legs
back on too.

=Dan

[ My Corner of Cyberspace http://ragooman.home.comcast.net/ ]

Grant Stockly wrote:
>
> This morning I tried to use the programmer "cold" and it failed. At least
> its not "me". The problem is for sure in the programmer or interface
> card. The symptom of only programming every other byte and not
> programming
> the bytes that it did do correctly is reflected in the logic analyzer
> reading. I have uploaded two more files. One is a picture of the problem
> and the other is a 170 second log of what happened on the programmer.
>
> A noticed that quite a few of the ICs legs are tarnished. Some are almost
> black. This must have been from an incompatible IC and socket combo. What
> is the best way to clean these ICs? Its possible that as things heat up
> the legs scrape a little and get better contact? Even if the ICs are
> cleaned, a tarnished IC must mean that the socket is bad too, right?
>
> I have a Altair 680 Ram card from Tom that has golden pin ram chips. All
> of the chips have pins that are literally cracking off. I would think
> that
> this is because of some anode/cathode thing going on. Its not the gold,
> but the steel or what ever the legs are made of. Some crack off and some
> even break off when the chips are removed from the sockets. The other ram
> card I have of his has non gold plated pin 4200 chips and they are all
> fine. Same sockets.
>
> Tarnished sockets and pins is something we have to look out for in these
> old computers...???
>
> Grant

[Grant Stockly]

From: "Steve"
Date: Sun, 03 Jun 2007 05:32:29 -0000
Subject: [Altair Computer Club] Re: 88-PPG Troubleshooting

Jack,

I don't know whether the "silver" pins are real silver or tin-lead,
but for the chips I experimented with, DeOxit didn't have much effect.

steve
=========================

--- In altaircomputerclub@yahoogroups.com, "jack99rubin"
<jack.rubin@...> wrote:
>
> > Usually, working the pins in and out of the socket several times
will
> > scrape through the insulating coating. ZIF sockets are a
different
> > matter, since they don't usually scrape the pins at all during
> > insertion. A trick I use with ZIFs is to partially squeeze the
> > chip's pins by partially closing the clamping lever. This grips
the
> > chip, but loosely enough that I can still slide the chip left and
> > right in the socket a few times, causing the pins to be scraped
off
> > for better contact. I ALWAYS do this when I blast old EPROMs,
even
> > if they look OK.
> >
> > It's tough to solder to such pins, too.
> >
> > Some day, I'll buy a bottle of Tarn-X tarnish remover and give it
a
> > try.
> >
>
> Be careful with Tarn-X since it apparently actually removes a bit
of
> silver in the polishing process. Whether or not you use Tarn-X, be
sure
> to follow up with Caig Labs ProGold. I prefer Caig DeOxit, followed
by
> the ProGold. They breakdown oxide, provide lubrication and maintain
> conductivity. Same treatment for switches too.
>
> Jack

[Grant Stockly]

From: "jack99rubin"
Date: Sun, 03 Jun 2007 12:20:53 -0000
Subject: [Altair Computer Club] Re: 88-PPG Troubleshooting

My experience with the Caig products has been mostly with Heathkit
stuff that wasn't "dark oxidized". It certainly helped with
intermittent contacts and fretting corrosion. It also noticeably
lessens the insertion force on chips.

The nice thing about the Caig stuff is that is inert and has the lab
studies to show it. I don't know about Tarn-X.

There's lot of info on this sort of stuff in the radio and audio
groups. The guys restoring ham and military gear seem to know their
stuff; the audiofools tend to get a bit a carried away...

Jack

--- In altaircomputerclub@yahoogroups.com, "Steve" <alltare@...>
wrote:
>
> Jack,
>
> I don't know whether the "silver" pins are real silver or tin-lead,
> but for the chips I experimented with, DeOxit didn't have much
effect.
>
> steve
> =========================
>
> --- In altaircomputerclub@yahoogroups.com, "jack99rubin"
> <jack.rubin@> wrote:
> >
> > > Usually, working the pins in and out of the socket several
times
> will
> > > scrape through the insulating coating. ZIF sockets are a
> different
> > > matter, since they don't usually scrape the pins at all during
> > > insertion. A trick I use with ZIFs is to partially squeeze the
> > > chip's pins by partially closing the clamping lever. This
grips
> the
> > > chip, but loosely enough that I can still slide the chip left
and
> > > right in the socket a few times, causing the pins to be scraped
> off
> > > for better contact. I ALWAYS do this when I blast old EPROMs,
> even
> > > if they look OK.
> > >
> > > It's tough to solder to such pins, too.
> > >
> > > Some day, I'll buy a bottle of Tarn-X tarnish remover and give
it
> a
> > > try.
> > >
> >
> > Be careful with Tarn-X since it apparently actually removes a bit
> of
> > silver in the polishing process. Whether or not you use Tarn-X,
be
> sure
> > to follow up with Caig Labs ProGold. I prefer Caig DeOxit,
followed
> by
> > the ProGold. They breakdown oxide, provide lubrication and
maintain
> > conductivity. Same treatment for switches too.
> >
> > Jack

[Grant Stockly]

From: "jack99rubin"
Date: Sun, 03 Jun 2007 12:48:32 -0000
Subject: [Altair Computer Club] Re: 88-PPG fixed with story

Thanks for another interesting chapter - hope you're writing a book
on demon chasing! Again, I'm guessing at the final resolution - you
resoldered the pin and all was well?

Another tool you've mentioned in passing is a desoldering pump - I
recently picked up a discontinued Hakko unit and it has made a
tremendous difference in my approach to these sorts of problems - it
is so easy to remove junk components like cheap or broken sockets
that I don't think twice about replacing them. I've used "the pump"
to salvage 40-pin IDE header connector of multilayer PC motherboards
so it's definitely up to the task of dealing with '70s era stuff.

I join H.E.Bob in congratulating you on repairing the PPG unit - it
sat in my attic for years until it went to Bob a while back. I never
used it but I'm glad to see it alive and well.

best,
Jack

--- In altaircomputerclub@yahoogroups.com, Grant Stockly <grant@...>
wrote:
>
> Using the data from the logic analyzer I traced out the problem
with the
> 88-PPG and fixed it. This makes me happy and I'm sure Robert
too. :
> ) Btw Robert if you are reading this please call or e-mail me! : )
>
> I've uploaded all data sheets for the ICs listed and a ton more
stuf in the
> file area. All you digital pack rats should go take a look at
it. : )
>
> There is also a picture of a 88-PMC ROM card with a ZIF socket
> installed. This allows me to swap ICs without removing the card.
>
> ===
>
> A0 is stuck high. This causes no odd bytes to be programmed and
all even
> bytes to be programmed twice with data from the associated odd
byte. : (
>
> There is a section on the motherboard where A0 is buffered twice.
The
> input to the circuit is 0-5v TTL and the output is -48-0v. A0 is
stuck
> high before this. A0 is generated by a 7400 positive NAND gate, 4Y
(pin
> 11). Pin 13 is high. Pin 12 needs to be high in order to make pin
11
> low. Pin 12 goes to a 8212, an 8 bit I/O port, pin 4 where it is
stuck low.
>
> Pin 4 on the 8212 is DO1 (data out bit 1 of 8). Pin 3 is the
associated
> DI1 (data in bit 1 of 8).
>
> There is no activity on pin 3 of the 8212. The 8212 is not bad.
>
> Pin 3, DI1, is shared on all 3 of the 8212s. If it is stuck low
then D0
> should be stuck low too. I checked the wave form and D0 NEVER goes
> high. Hmmm... : ) A0 stuck high, D0 stuck low. This makes sense
since
> the data lines are inverted compared to the data.
>
> Pin 3 on the 8212 goes to pin 2 of a 74LS14 a Hex Schmitt-Trigger
> Inverter. Pin 2 is an output, pin 1 is its input. This is one of
the
> tarnished ICs... Nothing at all on pin 1.
>
> Pin 1 on the 74LS14 connects to R11, R12, and pin 9 on the system
interface
> cable. No signal there either. There is no signal on pin 9 of the
S-100
> interface card either.
>
> The problem is in the interface card. Its pretty simple. : )
>
> Pin 9 on the interface cable goes to:
> -pin 24 on an unidentified empty socket.
> -pin 3 of IC D, a 74367 a Hex Buffer Driver with tri state output
> -pin 6 of IC G, a 8836 (quad NOR gate, sorry no datasheet)
>
> The 8836 pin is an input, so unless it is shorting then it isn't
the
> problem (I have seen this...).
>
> The legs on IC D are tarnished a nice dark black color. : ) Pin 3
is an
> output, pin 2 is the input to that buffer. Pin 3 on the IC socket
was not
> soldered very well at all. Looked like someone blew their nose on
> it. This is weird because the rest of the board is nice and
shiny. When
> it heated up it must have pulled tight against the board. I
noticed that
> the when sticking a wire into the socket it had no resistance and
when
> pulling it out it varied between 200 and 5 ohms. : )
>
> It works now! : ) I just copied the PPD ROM and used it to make
copies of
> other ROMs. : )
>
> Grant

[Grant Stockly]

From: "Steve"
Date: Sun, 03 Jun 2007 16:18:14 -0000
Subject: [Altair Computer Club] Re: 88-PPG fixed with story

Congratulations, Grant. It's nice to know there's still a
functioning programmer out there. Does this mean that your PPC PROM
was good after all, or do you still need a good one?

Steve
========================================

--- In altaircomputerclub@yahoogroups.com, Grant Stockly <grant@...>
wrote:
>
> Using the data from the logic analyzer I traced out the problem
with the
> 88-PPG and fixed it. This makes me happy and I'm sure Robert
too. :
> ) Btw Robert if you are reading this please call or e-mail me! : )
>
> I've uploaded all data sheets for the ICs listed and a ton more
stuf in the
> file area. All you digital pack rats should go take a look at
it. : )
>
> There is also a picture of a 88-PMC ROM card with a ZIF socket
> installed. This allows me to swap ICs without removing the card.
>
> ===
>
> A0 is stuck high. This causes no odd bytes to be programmed and
all even
> bytes to be programmed twice with data from the associated odd
byte. : (
>
> There is a section on the motherboard where A0 is buffered twice.
The
> input to the circuit is 0-5v TTL and the output is -48-0v. A0 is
stuck
> high before this. A0 is generated by a 7400 positive NAND gate, 4Y
(pin
> 11). Pin 13 is high. Pin 12 needs to be high in order to make pin
11
> low. Pin 12 goes to a 8212, an 8 bit I/O port, pin 4 where it is
stuck low.
>
> Pin 4 on the 8212 is DO1 (data out bit 1 of 8). Pin 3 is the
associated
> DI1 (data in bit 1 of 8).
>
> There is no activity on pin 3 of the 8212. The 8212 is not bad.
>
> Pin 3, DI1, is shared on all 3 of the 8212s. If it is stuck low
then D0
> should be stuck low too. I checked the wave form and D0 NEVER goes
> high. Hmmm... : ) A0 stuck high, D0 stuck low. This makes sense
since
> the data lines are inverted compared to the data.
>
> Pin 3 on the 8212 goes to pin 2 of a 74LS14 a Hex Schmitt-Trigger
> Inverter. Pin 2 is an output, pin 1 is its input. This is one of
the
> tarnished ICs... Nothing at all on pin 1.
>
> Pin 1 on the 74LS14 connects to R11, R12, and pin 9 on the system
interface
> cable. No signal there either. There is no signal on pin 9 of the
S-100
> interface card either.
>
> The problem is in the interface card. Its pretty simple. : )
>
> Pin 9 on the interface cable goes to:
> -pin 24 on an unidentified empty socket.
> -pin 3 of IC D, a 74367 a Hex Buffer Driver with tri state output
> -pin 6 of IC G, a 8836 (quad NOR gate, sorry no datasheet)
>
> The 8836 pin is an input, so unless it is shorting then it isn't
the
> problem (I have seen this...).
>
> The legs on IC D are tarnished a nice dark black color. : ) Pin 3
is an
> output, pin 2 is the input to that buffer. Pin 3 on the IC socket
was not
> soldered very well at all. Looked like someone blew their nose on
> it. This is weird because the rest of the board is nice and
shiny. When
> it heated up it must have pulled tight against the board. I
noticed that
> the when sticking a wire into the socket it had no resistance and
when
> pulling it out it varied between 200 and 5 ohms. : )
>
> It works now! : ) I just copied the PPD ROM and used it to make
copies of
> other ROMs. : )
>
> Grant