Super 80 – Hardware Notes

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Using 2532 and 2732A EPROMs with the V1 PCB

The “standard” (unmodified) Super 80 PCB, and the V1 Reproduction, are wired to work with 2516 or 2716 EPROMs only. You can use either a 2516 or a 2716 without any modifications to the standard PCB.

To instead use 2532 EPROMs, you need to follow the instructions shown on my V1 KiCAD Schematic, namely:

• Cut the bottom layer PCB trace between U26 Pin 20 and the pad immediately adjacent to it (which is JP1 Pin 1). This prevents the /ROM0 signal (fed from Pin 20) from reaching Pin 18 of each EPROM (it remains connected to Pin 20 of U26 however, and Pin 18 of each EPROM continues to be connected together).
• Put a link on the bottom layer of the PCB between JP1 Pin 1 and JP2 Pin 2. This connects A11 (which is present on JP1 Pin 2) to Pin 18 of each EPROM.

To instead use 2732A EPROMs, the modifications are more extensive. We need to make the following changes:

• Pin 18 (/CE) needs to be connected to the individual rom-enable signals (On the unmodified S80, Pin 18 of the 3 EPROMs are currently connected together, and they are then driven by /ROM0 from Pin 20 of U26).
• Pin 20 (/OE) needs to be low during read, and its level does not matter during standby mode. Currently (on the unmodified S80) it is connected to the relevant rom-enable signal. So no change is needed here.
• Pin 21 (A11) needs to be connected to A11 (on the unmodified S80, Pin 21 of the 3 EPROMs are currently connected together, and they are then connected to VCC by a bottom-layer PCB trace between U26 Pin 21 and U26 Pin 24).

So here are the changes that we need to make to the “standard” Super 80 PCB (or V1 Reproduction PCB), to use 2732A EPROMs:

• Check that your S80 is in “standard” configuration (ie U26 Pin 20 is connected to JP1 Pin 1 on the bottom layer of the PCB, and there is no link between JP1 Pin 1 and JP1 Pin 2).
• At present Pin 18 of the 3 EPROMs (U26, U33 and U42) are connected together. We need to isolate them, as they are the /CE input for each 2732A. So firstly between U26 and U33, carefully cut the top-layer trace that leads away from U26 Pin 18. Secondly, between U33 and U42, carefully cut the top-layer trace that leads away from U33 Pin 18.
• On the bottom layer, link U33 Pin 20 (which is the /ROM1 signal) to U33 Pin 18 (which is the /CE input).
• On the bottom layer, link U42 Pin 20 (which is the /ROM2 signal) to U42 Pin 18 (which is the /CE input).
• On the bottom layer, cut the trace between U26 Pin 21 and U26 Pin 24. This isolates Pin 21 of each EPROM (which continue to be connected together) from VCC.
• On the bottom layer, link JP1 Pin 2 (which is adjacent to U26 Pin 21) to U26 Pin 21. This feeds A11 (which is present on JP1 Pin 2) to Pin 21 of each EPROM.

Transformers and Power Supplies

Transformers

The transformer used in the original Super 80 was Dick Smith Electronics’ P/N M2325, as shown here on the right. This transformer (according to a schematic that I have) describes it as having a 12-0-12 winding rated at 1 Amp, and a 7VAC winding also rated at 1 Amp. The 12-0-12 is not a single winding, but two separate 12V windings connected end-to-end.

Here are some observed voltage measurements with the M2325 transformer:

• AC RMS primary voltage: 239 VAC
• AC RMS secondary voltages with no load: 7.39 and 13.5-0.13.5
• AC RMS secondary voltages with board connected: 7.25 and 13.3-0-13.3
• Input to 7805 regulators: 8.00 VDC
• Input to 7812 regulator: 16.7 VDC
• Input to 7905 regulator: -17.8 VDC

Unfortunately I’ve not been able to locate the M2325, or any suitable replacement, at any Australian electronics stores. I have however found Signal Transformer’s P/N A41-80-512 on Digikey’s website, as pictured on the right here. The datasheet (which is no longer on Digikey’s website) shows that this transformer is designed to deliver (through a power supply with linear voltage regulators) +5V at 3.5A and +/-12V at 600mA. It sounds ideal. Back in 2014, this was priced at around US$50. Now (January 2018) the Digikey price has halved to US$25, but they have no stock. I wrote to Digikey and they said it has a 12-week lead time. I placed an order for 2 of these, and they arrived about 3-4 weeks later. I also wrote to the manufacturer (Signal Transformer). They will sell direct, but they won’t post to Australia. So ordering from Digikey seems to be the best approach for the time being.

The datasheet for the A41-80-512 doesn’t publish the VAC output voltages, but here are some observed measurements:

• AC RMS primary voltage: 241 VAC
• AC RMS secondary voltages with no load: 10.5 and 16.3-0-16.3
• AC RMS secondary voltages with board connected: 10.4 and 16.3-0.16.3
• Input to 7805 regulators: 12.2 VDC
• Input to 7812 regulator: 20.8 VDC
• Input to 7905 regulator: -21.9 VDC

The A41-80-512 seems to work fine as a substitute for the M2325. However, note that the voltage regulators need to drop almost twice the amount of DC voltage (to deliver the intended DC output voltages), meaning that almost twice the amount of waste heat will be generated.

A third option that I came up with is a transformer I obtained from a surplus parts store. It is marked as “JED 007”. It has voltage outputs marked as 14-0-14 and 8V. The actual RMS VAC outputs are much higher. Here are some observed measurements:

• AC RMS primary voltage: [Not measured]
• AC RMS secondary voltages with no load: 9.4 and 16.5-0-16.5
• AC RMS secondary voltages with board connected: 9.1 and 16.4-0.16.4
• Input to 7805 regulators: 10.5 VDC
• Input to 7812 regulator: 21.5 VDC
• Input to 7905 regulator: -21.9 VDC

get 10.5V at the input of the 7805s, 21.5V at the input to the 7812, and -21.9V at the input to the 7905

External DC Power Supplies

Another option is to feed DC into the S80 PCB (but without modifying the S80 in any way). I figure this can be done with the following Meanwell Products:

• NES-100-7.5: Adjustable 7.13V to 8.3V at 13.6A; or
• NES-100-9: Adjustable 8.55V to 9.9V at 11.2A
• NET-75C: 5V/6A (which we would leave disconnected), +15V/2.3A and -15V/0.5A

The NES-100-7.5 or NES-100-9 could be used to drive the +8V rail (via diode CR3). The NET-75C’s +15V and -15V outputs could drive the +16V and -16V rails (via diodes CR7 and CR5 respectively). I haven’t tried this out yet. I suspect the NES-100-7.5 might not deliver a high enough voltage to the +8V rail, due to the 0.9V drop across diode CR3. So the NES-100-9 is probably the better choice.

Another option is to bypass all the rectifier diodes and voltage regulators on the S80 and drive the +5V rails (there are two of them) and the +12V and -12V rails with a multi-output switch-mode power supply. Meanwell’s RQ-65B would be ideal for this: +5V/6A, +12V/2A, -5V/0.5A, -12V/0.5A.

There are many other Meanwell power supplies that could be useful, depending on how you want to power the S80. Keep in mind that if you chose to bypass the S80’s on-board voltage regulators then you will not be able to supply the higher “unregulated” DC voltages delivered to the S100 slot. So you will also need to bypass the regulators on any S100 board that you insert. Here are some of the more relevant models:

• PD-2515: Open frame +/-15V supply. Low current rating
• TP-75C: +5V/6A, +15V/2.5A, -15V/0.5A
• TP-75B: +5V/7A, +12V/3A, -12V/0.4V
• MPT-65A: +5V/5.5A, +12V/2.5A, -5V/0.5A
• T-50A: +5V/7A, +12V/2.5A, -5V/0.5A
• NET-35B: +5V/3A, +12V/1.0A, -12V/0.5A
• RQ-85B: +5V/7A, +12V/3.1A, -5V/0.5A, -12V/0.5A
• RT-85C: +5V/7A, +15V/3A, -15V/0.5A
• EPS-25-7.5: 7.5V/4.7A
• PT-65A: +5V/5.5A, +12V/2.5A, -5V/0.5A

2513 Character Generator

The Super 80 uses a character generator chip specified only as a “2513”. The problem is that not all 2513s are the same.

The 2513 shown on the right is a 2513 from an original Super 80. This is the General Instrument RO-3-2513 with CGR-001 character set. The RO-3-2513 is a single-rail chip (it requires only +5V). This chip is proving to be very hard to find. I was fortunate to fine one at Netty Electronics in Canada. However, it was the only one that he had in stock.

My RO-3-2513 CGR-001 will be used in a V1 Reproduction PCB. It hasn’t arrived at the time of writing this, but a picture of it is shown on the right here.

The datasheet for the RO-3-2513 is available here on stardot.org.uk. A further copy (which also includes other GI ROMs) is available here on bitsavers.trailing-edge.com.

If you are looking for an RO-3-2513, it is important to be aware that there are multiple versions of this chip that contain differing character sets. The one we want for the Super 80 is the “CGR-001”. The character set for the CGR-001 is shown on the right here (click on the image for a larger version).

The RO-3-2513 variant that is easiest to find online is the CGR-002, which it seems may have been used in the Apple II (I am not 100% sure about this). I don’t know what the differences are between the CGR-001 and the CGR-002. If you have any information about the CGR-002, please let me know.

An earlier version of the 2513 is the Signetics 2513. The datasheet for the Signetics 2513 is available here on amigan.yatho.com. The Signetics 2513N is still available from Anchor Electronics as at February 2018.

A picture of the Signetics 2513 is shown on the right here.

The biggest downside of the Signetics 2513 is that it requires 3 voltages: +5V on Pin 24, -12V on Pin 1, and -5V on Pin 12. Unfortunately both the original Super 80 and the V1 Reproduction PCB do not accommodate this, as both pins 1 and 12 on the PCB are not connected to anything.

The Signetics 2513 datasheet reveals that the standard character set for this chip is known as CM2140.

The CM2140 character set is shown here on the right.

The good news is that the Signetics 2513 can be made to work on the original Super 80 (or the V1 Reproduction PCB). Here are the instructions needed to provide -12V to Pin 1m and -5V to Pin 12:

• To generate the -12V, solder in place a 79L12 voltage regulator directly under the exiting 7905 voltage regulator (U2). Install the 79L12 on the underside of the PCB.
• The output from the 79L12 gets wired directly to Pin 1 of the 2513 IC socket (U23).
• Then install a 0.1uF capacitor on the underside of the PCB, between Pin 1 of U23 and the adjacent Pin 7 of U28 (GND).
• Supply -5V to the Signetics 2513 by wiring Pin 1 of U53 to Pin Pin 12 of U23.

Here are some photos showing the modifications to the underside of the V1 Reproduction PCB to accommodate the Signetics 2513N.

Here are some other links relevant to the 2513:

Source for CGR-002 version of the RO-3-2513 (as used in the Apple II)

U.S. RFQ Supplier of CGR-001 version (I have sent an online enquiry)

Rochester Electronics’ webpage showing stock of RO-3-2513 (I have sent them an email asking whether these are CGR-001 versions).

Heatsink and temperatures

[This section is under construction today (Sun 4 March 2018). Check back later for final version]

[insert photo of original heatsinks]

The original Super 80 used two L-shaped plain aluminium heatsinks (one on each 7805). [insert dimensions]. The 7812 and 7905 had no heatsink fitted.

I fabricated a single-piece heatsink to accommodate both 7805s [insert photo]. It is a 68mm length of 25x25x[1.6] aluminium angle. On the bottom flange (the one that sits on the PCB) I drilled two 3.5mm holes. Measured on the outside face, both holes are 12mm from the edge facing the 4116 RAMs. The first is 17mm from the end adjacent to the 7912 regulator, and the second is 52.5mm from the 7912. I used a can of satin black spray paint to paint mine, but powder coating would be better.

[Insert photo of M2325 transformer]

The transformer originally specified for the Super 80 was an M2325. I have not been able to find any currently-available source for this transformer. I believe this transfer had 2 x 12V windings and 1 x 5V winding. [verify this]

I’m using a transformer from a surplus electronics shop to power my V1 Super 80. It is marked “JED 007” and has outputs marked as 14-0-14 and 8V. I haven’t been able to find a datasheet for this transformer, so I can’t be sure of the output capacity. But it seems to run the V1 Reproduction just fine. With no load, the secondaries measure 16.5-0-16.5 VAC and 9.4 VAC respectively. When powering the S80, those AC voltages only drop marginally (to 16.4-0-16.4 and 9.1).

When powered by the JED 007, I get 10.5V at the input of the 7805s, 21.5V at the input to the 7812, and -21.9V at the input to the 7905. Clearly these are on the high side, resulting in the regulators having to drop almost 50% of the DC voltages (and thereby putting the devices under some stress, due to the heat dissipation). Still, it seems to be acceptable. Here are the measured temperatures (with one 2716 EPROM installed and only one bank of 4116s fitted):

• Ambient temperature: 25.0
• Heatsink lower flange: 43.0
• Heatsink upper flange: 53.0
• 7805 mounting tabs: 54.5 and 53.o
• 7805 plastic body: 42.0 and 40.0
• 7812 mounting tab: 41.0
• 7812 plastic body: 38.0
• 7905 mounting tab: 41.0
• 7905 body: 31.0
• Transformer: 30.0
• Regulator diodes: Approx 35-45

81LS85 and 81LS97

A fully populated Super 80 uses 5 of these ICs:

• U5 (81LS95/81LS97): U5 and U13 are output buffers for A0-A15
• U10 (81LS95/81LS97): Receive cassette input, read 4-way dipswitch, read I/O pins 7 & 8.
• U13 (81LS95/81LS97): U5 and U13 are output buffers for A0-A15
• U4 (81LS95): Receive D0-D7 from S100 bus
• U12 (81LS95/81LS97): Transmit D0-D7 to S100 bus

Note that U4 and U12 are only required if the S100 slot will be used.

The reason that U4 must be an 81LS95 is that the two Output Enable signals (pins 1 and 19) are driven by different input signals. The other 4 ICs (U5, U10, U13 and U12) have pins 1 and 19 tied together. That is why they can use either an 81LS85 or an 81LS97.